diff --git a/routes/bills.js b/routes/bills.js
index 27bdb6a..1122cc8 100644
--- a/routes/bills.js
+++ b/routes/bills.js
@@ -17,7 +17,7 @@ const { standardizeError } = require('../middleware/errorFormatter');
 const { validatePaymentInput, serializePayment } = require('../services/paymentValidation.cts');
 const { addMerchantRule, syncBillPaymentsFromSimplefin, merchantMatches } = require('../services/billMerchantRuleService.cts');
 const { normalizeMerchant } = require('../services/subscriptionService');
-const { decorateTransaction } = require('../services/transactionService');
+const { decorateTransaction } = require('../services/transactionService.cts');
 const {
   accountingActiveSql,
   applyBankPaymentAsSourceOfTruth,
diff --git a/routes/calendar.js b/routes/calendar.js
index 8733fe7..0bb1089 100644
--- a/routes/calendar.js
+++ b/routes/calendar.js
@@ -12,7 +12,7 @@ const {
   previewFeed,
   regenerateToken,
   revokeToken,
-} = require('../services/calendarFeedService');
+} = require('../services/calendarFeedService.cts');
 const { localDateString } = require('../utils/dates.mts');
 const { roundMoney, sumMoney, fromCents } = require('../utils/money.mts');
 
diff --git a/routes/calendarFeed.js b/routes/calendarFeed.js
index 9bb3796..0d81217 100644
--- a/routes/calendarFeed.js
+++ b/routes/calendarFeed.js
@@ -6,7 +6,7 @@ const {
   buildCalendarFeed,
   getTokenRecord,
   markTokenUsed,
-} = require('../services/calendarFeedService');
+} = require('../services/calendarFeedService.cts');
 
 // GET /api/calendar/feed.ics?token=...
 // Public by design: calendar clients cannot use the app's session cookies.
diff --git a/routes/dataSources.js b/routes/dataSources.js
index a51e925..b04137e 100644
--- a/routes/dataSources.js
+++ b/routes/dataSources.js
@@ -3,7 +3,7 @@
 const router = require('express').Router();
 const { getDb }                                    = require('../db/database');
 const { standardizeError }                         = require('../middleware/errorFormatter');
-const { decorateDataSource, ensureManualDataSource } = require('../services/transactionService');
+const { decorateDataSource, ensureManualDataSource } = require('../services/transactionService.cts');
 const { connectSimplefin, syncDataSource, backfillDataSource, disconnectDataSource } = require('../services/bankSyncService');
 const { sanitizeErrorMessage }                     = require('../services/simplefinService');
 const { getBankSyncConfig }                        = require('../services/bankSyncConfigService.cts');
diff --git a/routes/matches.js b/routes/matches.js
index 87ac30b..a3bdc5c 100644
--- a/routes/matches.js
+++ b/routes/matches.js
@@ -5,7 +5,7 @@ const { applyBankPaymentAsSourceOfTruth, reactivatePaymentsOverriddenBy } = requ
 const {
   listMatchSuggestions,
   rejectMatchSuggestion,
-} = require('../services/matchSuggestionService');
+} = require('../services/matchSuggestionService.cts');
 const { learnMerchantRuleFromMatch } = require('../services/billMerchantRuleService.cts');
 const { markMatched, markUnmatched } = require('../services/transactionMatchState.cts');
 const { serializePayment } = require('../services/paymentValidation.cts');
diff --git a/routes/snowball.js b/routes/snowball.js
index 9b99454..d2b4aea 100644
--- a/routes/snowball.js
+++ b/routes/snowball.js
@@ -2,7 +2,7 @@ const express = require('express');
 const router = express.Router();
 const { getDb } = require('../db/database');
 const { standardizeError } = require('../middleware/errorFormatter');
-const { calculateSnowball, calculateAvalanche } = require('../services/snowballService');
+const { calculateSnowball, calculateAvalanche } = require('../services/snowballService.cts');
 const { calculateMinimumOnly, debtAprSnapshot } = require('../services/aprService.cts');
 const { serializeBill } = require('../services/billsService');
 const { toCents, fromCents } = require('../utils/money.mts');
diff --git a/routes/transactions.js b/routes/transactions.js
index 16f9542..cc658b4 100644
--- a/routes/transactions.js
+++ b/routes/transactions.js
@@ -5,7 +5,7 @@ const {
   decorateTransaction,
   ensureManualDataSource,
   getTransactionForUser,
-} = require('../services/transactionService');
+} = require('../services/transactionService.cts');
 const { checkTransaction: advisoryCheck } = require('../services/advisoryFilterService.cts');
 const { getBankSyncConfig } = require('../services/bankSyncConfigService.cts');
 const { markUnmatched } = require('../services/transactionMatchState.cts');
@@ -14,13 +14,13 @@ const {
   matchTransactionToBill,
   unignoreTransaction,
   unmatchTransaction,
-} = require('../services/transactionMatchService');
+} = require('../services/transactionMatchService.cts');
 const { reactivatePaymentsOverriddenBy } = require('../services/paymentAccountingService.cts');
 const {
   findMerchantMatch,
   applyMerchantStoreMatches,
   findOrCreateCategory,
-} = require('../services/merchantStoreMatchService');
+} = require('../services/merchantStoreMatchService.cts');
 const { categorizeTransaction } = require('../services/spendingService.cts');
 const { todayLocal } = require('../utils/dates.mts');
 const { roundMoney } = require('../utils/money.mts');
diff --git a/services/bankSyncService.js b/services/bankSyncService.js
index 93aaef8..13e97af 100644
--- a/services/bankSyncService.js
+++ b/services/bankSyncService.js
@@ -9,11 +9,11 @@ const {
   sanitizeErrorMessage,
 } = require('./simplefinService');
 const { getBankSyncConfig, SYNC_DAYS_EFFECTIVE, SYNC_DAYS_DEFAULT } = require('./bankSyncConfigService.cts');
-const { decorateDataSource } = require('./transactionService');
+const { decorateDataSource } = require('./transactionService.cts');
 const { applyMerchantRules } = require('./billMerchantRuleService.cts');
 const { applySpendingCategoryRules } = require('./spendingService.cts');
-const { applyMerchantStoreMatches } = require('./merchantStoreMatchService');
-const { autoMatchForUser } = require('./matchSuggestionService');
+const { applyMerchantStoreMatches } = require('./merchantStoreMatchService.cts');
+const { autoMatchForUser } = require('./matchSuggestionService.cts');
 const { getUserSettings } = require('./userSettings');
 
 function sinceEpochDays(days) {
diff --git a/services/calendarFeedService.js b/services/calendarFeedService.cts
similarity index 79%
rename from services/calendarFeedService.js
rename to services/calendarFeedService.cts
index d3cb8de..89bb453 100644
--- a/services/calendarFeedService.js
+++ b/services/calendarFeedService.cts
@@ -1,15 +1,20 @@
 'use strict';
 
+import type { Db } from '../types/db';
+import type { Req } from '../types/http';
+
 const crypto = require('crypto');
 const { getDb } = require('../db/database');
 const { normalizeCycleType, resolveDueDate } = require('./statusService.cts');
-const { fromCents } = require('../utils/money.mts');
+const { fromCents } = require('../utils/money.mts') as typeof import('../utils/money.mts');
+
+type Row = Record<string, any>;
 
 const PRODID = '-//Bill Tracker//Calendar Feed//EN';
 const FEED_PAST_MONTHS = 12;
 const FEED_FUTURE_MONTHS = 24;
 
-const WEEKDAY_CODES = {
+const WEEKDAY_CODES: Record<string, string> = {
   sunday: 'SU',
   monday: 'MO',
   tuesday: 'TU',
@@ -19,7 +24,7 @@ const WEEKDAY_CODES = {
   saturday: 'SA',
 };
 
-function ensureCalendarTokenSchema(db = getDb()) {
+function ensureCalendarTokenSchema(db: Db = getDb()): void {
   db.exec(`
     CREATE TABLE IF NOT EXISTS calendar_tokens (
       id INTEGER PRIMARY KEY AUTOINCREMENT,
@@ -36,16 +41,16 @@ function ensureCalendarTokenSchema(db = getDb()) {
   `);
 }
 
-function generateToken() {
+function generateToken(): string {
   return crypto.randomBytes(32).toString('base64url');
 }
 
-function sanitizeLabel(label) {
+function sanitizeLabel(label: unknown): string {
   const value = String(label || 'Bill Tracker Calendar').trim();
   return value.slice(0, 80) || 'Bill Tracker Calendar';
 }
 
-function getActiveToken(userId, db = getDb()) {
+function getActiveToken(userId: number, db: Db = getDb()): Row | null {
   ensureCalendarTokenSchema(db);
   return db.prepare(`
     SELECT id, user_id, token, label, active, last_used_at, created_at, revoked_at
@@ -56,7 +61,7 @@ function getActiveToken(userId, db = getDb()) {
   `).get(userId) || null;
 }
 
-function createToken(userId, label = 'Bill Tracker Calendar', db = getDb()) {
+function createToken(userId: number, label = 'Bill Tracker Calendar', db: Db = getDb()): Row {
   ensureCalendarTokenSchema(db);
   const token = generateToken();
   const result = db.prepare(`
@@ -70,13 +75,13 @@ function createToken(userId, label = 'Bill Tracker Calendar', db = getDb()) {
   `).get(result.lastInsertRowid);
 }
 
-function getOrCreateToken(userId, db = getDb()) {
+function getOrCreateToken(userId: number, db: Db = getDb()): Row {
   return getActiveToken(userId, db) || createToken(userId, 'Bill Tracker Calendar', db);
 }
 
-function regenerateToken(userId, db = getDb()) {
+function regenerateToken(userId: number, db: Db = getDb()): Row {
   ensureCalendarTokenSchema(db);
-  let next;
+  let next: Row;
   db.transaction(() => {
     db.prepare(`
       UPDATE calendar_tokens
@@ -85,10 +90,10 @@ function regenerateToken(userId, db = getDb()) {
     `).run(userId);
     next = createToken(userId, 'Bill Tracker Calendar', db);
   })();
-  return next;
+  return next!;
 }
 
-function revokeToken(userId, db = getDb()) {
+function revokeToken(userId: number, db: Db = getDb()): void {
   ensureCalendarTokenSchema(db);
   db.prepare(`
     UPDATE calendar_tokens
@@ -97,7 +102,7 @@ function revokeToken(userId, db = getDb()) {
   `).run(userId);
 }
 
-function getTokenRecord(token, db = getDb()) {
+function getTokenRecord(token: unknown, db: Db = getDb()): Row | null {
   ensureCalendarTokenSchema(db);
   if (!token || typeof token !== 'string') return null;
   return db.prepare(`
@@ -107,22 +112,22 @@ function getTokenRecord(token, db = getDb()) {
   `).get(token) || null;
 }
 
-function markTokenUsed(tokenId, db = getDb()) {
+function markTokenUsed(tokenId: number, db: Db = getDb()): void {
   ensureCalendarTokenSchema(db);
   db.prepare('UPDATE calendar_tokens SET last_used_at = datetime(\'now\') WHERE id = ?').run(tokenId);
 }
 
-function originFromRequest(req) {
+function originFromRequest(req: Req): string {
   const host = req.get?.('x-forwarded-host') || req.get?.('host') || 'localhost';
   const proto = req.get?.('x-forwarded-proto') || req.protocol || 'http';
   return `${String(proto).split(',')[0]}://${String(host).split(',')[0]}`;
 }
 
-function feedUrlForToken(req, token) {
+function feedUrlForToken(req: Req, token: string): string {
   return `${originFromRequest(req)}/api/calendar/feed.ics?token=${encodeURIComponent(token)}`;
 }
 
-function ymd(date) {
+function ymd(date: Date): string {
   return [
     date.getUTCFullYear(),
     String(date.getUTCMonth() + 1).padStart(2, '0'),
@@ -130,27 +135,27 @@ function ymd(date) {
   ].join('-');
 }
 
-function icsDate(dateString) {
+function icsDate(dateString: unknown): string {
   return String(dateString).replaceAll('-', '');
 }
 
-function utcStamp(date = new Date()) {
+function utcStamp(date: Date = new Date()): string {
   return date.toISOString().replace(/[-:]/g, '').replace(/\.\d{3}Z$/, 'Z');
 }
 
-function addDays(dateString, days) {
+function addDays(dateString: unknown, days: number): string {
   const [year, month, day] = String(dateString).split('-').map(Number);
   const date = new Date(Date.UTC(year, month - 1, day));
   date.setUTCDate(date.getUTCDate() + days);
   return ymd(date);
 }
 
-function addMonths(date, months) {
+function addMonths(date: Date, months: number): Date {
   return new Date(Date.UTC(date.getUTCFullYear(), date.getUTCMonth() + months, 1));
 }
 
-function monthIterator(startDate, endDate) {
-  const months = [];
+function monthIterator(startDate: Date, endDate: Date): { year: number; month: number }[] {
+  const months: { year: number; month: number }[] = [];
   let cursor = new Date(Date.UTC(startDate.getUTCFullYear(), startDate.getUTCMonth(), 1));
   const end = new Date(Date.UTC(endDate.getUTCFullYear(), endDate.getUTCMonth(), 1));
   while (cursor <= end) {
@@ -161,7 +166,7 @@ function monthIterator(startDate, endDate) {
 }
 
 // RFC 5545 §3.3.11 TEXT: escape backslash, semicolon, comma, and line breaks.
-function escapeText(value) {
+function escapeText(value: unknown): string {
   return String(value ?? '')
     .replace(/\\/g, '\\\\')
     .replace(/\r\n|\r|\n/g, '\\n')
@@ -170,11 +175,11 @@ function escapeText(value) {
 }
 
 // RFC 5545 §3.1 content lines: fold at 75 octets, not JavaScript characters.
-function foldLine(line) {
+function foldLine(line: unknown): string {
   const value = String(line);
   if (Buffer.byteLength(value, 'utf8') <= 75) return value;
 
-  const lines = [];
+  const lines: string[] = [];
   let current = '';
   let limit = 75;
 
@@ -193,23 +198,23 @@ function foldLine(line) {
   return lines.map((part, index) => (index === 0 ? part : ` ${part}`)).join('\r\n');
 }
 
-function weekdayForCycleDay(value) {
+function weekdayForCycleDay(value: unknown): string {
   const normalized = String(value || 'monday').trim().toLowerCase();
   return WEEKDAY_CODES[normalized] || 'MO';
 }
 
-function monthForCycleDay(value) {
-  const parsed = parseInt(value, 10);
+function monthForCycleDay(value: unknown): number {
+  const parsed = parseInt(value as string, 10);
   return Number.isInteger(parsed) && parsed >= 1 && parsed <= 12 ? parsed : 1;
 }
 
-function dayForBill(bill) {
+function dayForBill(bill: Row): number {
   const parsed = parseInt(bill?.due_day, 10);
   return Number.isInteger(parsed) && parsed >= 1 && parsed <= 31 ? parsed : 1;
 }
 
 // RRULE values follow RFC 5545 §3.3.10 and mirror the app's five cycle types.
-function rruleForCycle(bill = {}) {
+function rruleForCycle(bill: Row = {}): string {
   const cycleType = normalizeCycleType(bill);
   if (cycleType === 'weekly') {
     return `FREQ=WEEKLY;BYDAY=${weekdayForCycleDay(bill.cycle_day)}`;
@@ -226,17 +231,17 @@ function rruleForCycle(bill = {}) {
   return `FREQ=MONTHLY;BYMONTHDAY=${dayForBill(bill)}`;
 }
 
-function eventUid(bill, dueDate) {
+function eventUid(bill: Row, dueDate: string): string {
   return `bill-tracker-bill-${bill.id}-${dueDate}@bill-tracker`;
 }
 
-function eventSummary(bill, detailLevel = 'standard') {
+function eventSummary(bill: Row, detailLevel = 'standard'): string {
   if (detailLevel === 'private') return 'Bill due';
   if (detailLevel === 'full') return `${bill.name} due - $${(fromCents(bill.expected_amount) || 0).toFixed(2)}`;
   return `${bill.name} due`;
 }
 
-function eventDescription(bill, dueDate, detailLevel = 'standard') {
+function eventDescription(bill: Row, dueDate: string, detailLevel = 'standard'): string {
   const lines = ['Bill Tracker reminder'];
   if (detailLevel !== 'private') lines.push(`Bill: ${bill.name}`);
   if (detailLevel === 'full') lines.push(`Expected amount: $${(fromCents(bill.expected_amount) || 0).toFixed(2)}`);
@@ -246,7 +251,7 @@ function eventDescription(bill, dueDate, detailLevel = 'standard') {
   return lines.join('\n');
 }
 
-function buildEvent({ bill, dueDate, detailLevel = 'standard', dtstamp = utcStamp() }) {
+function buildEvent({ bill, dueDate, detailLevel = 'standard', dtstamp = utcStamp() }: { bill: Row; dueDate: string; detailLevel?: string; dtstamp?: string }): string[] {
   const dtEnd = addDays(dueDate, 1);
   const lines = [
     'BEGIN:VEVENT',
@@ -264,7 +269,7 @@ function buildEvent({ bill, dueDate, detailLevel = 'standard', dtstamp = utcStam
   return lines;
 }
 
-function loadActiveBillsForFeed(userId, db = getDb()) {
+function loadActiveBillsForFeed(userId: number, db: Db = getDb()): Row[] {
   return db.prepare(`
     SELECT b.*, c.name AS category_name
     FROM bills b
@@ -276,14 +281,14 @@ function loadActiveBillsForFeed(userId, db = getDb()) {
   `).all(userId);
 }
 
-function buildFeedEvents(userId, options = {}, db = getDb()) {
+function buildFeedEvents(userId: number, options: Row = {}, db: Db = getDb()): any[] {
   const now = options.now || new Date();
   const start = options.startDate || addMonths(now, -(options.pastMonths ?? FEED_PAST_MONTHS));
   const end = options.endDate || addMonths(now, options.futureMonths ?? FEED_FUTURE_MONTHS);
   const detailLevel = options.detailLevel || 'standard';
   const dtstamp = options.dtstamp || utcStamp(now);
-  const events = [];
-  const seen = new Set();
+  const events: any[] = [];
+  const seen = new Set<string>();
 
   for (const bill of loadActiveBillsForFeed(userId, db)) {
     for (const { year, month } of monthIterator(start, end)) {
@@ -300,7 +305,7 @@ function buildFeedEvents(userId, options = {}, db = getDb()) {
   return events;
 }
 
-function buildIcsCalendar({ name = 'Bill Tracker', events = [] } = {}) {
+function buildIcsCalendar({ name = 'Bill Tracker', events = [] }: { name?: string; events?: any[] } = {}): string {
   const lines = [
     'BEGIN:VCALENDAR',
     'VERSION:2.0',
@@ -319,7 +324,7 @@ function buildIcsCalendar({ name = 'Bill Tracker', events = [] } = {}) {
   return `${lines.map(foldLine).join('\r\n')}\r\n`;
 }
 
-function buildCalendarFeed(userId, options = {}, db = getDb()) {
+function buildCalendarFeed(userId: number, options: Row = {}, db: Db = getDb()) {
   const events = buildFeedEvents(userId, options, db);
   return {
     ics: buildIcsCalendar({ name: options.name || 'Bill Tracker', events }),
@@ -327,7 +332,7 @@ function buildCalendarFeed(userId, options = {}, db = getDb()) {
   };
 }
 
-function previewFeed(userId, options = {}, db = getDb()) {
+function previewFeed(userId: number, options: Row = {}, db: Db = getDb()) {
   const events = buildFeedEvents(userId, { ...options, pastMonths: 0, futureMonths: 6 }, db);
   return events.slice(0, options.limit || 10).map(event => ({
     uid: event.uid,
diff --git a/services/csvTransactionImportService.js b/services/csvTransactionImportService.js
index 0bb2e09..4eb1fd6 100644
--- a/services/csvTransactionImportService.js
+++ b/services/csvTransactionImportService.js
@@ -2,7 +2,7 @@
 
 const crypto = require('crypto');
 const { getDb } = require('../db/database');
-const { decorateTransaction, ensureManualDataSource } = require('./transactionService');
+const { decorateTransaction, ensureManualDataSource } = require('./transactionService.cts');
 
 const SESSION_TTL_MS = 24 * 60 * 60 * 1000;
 const MAX_ROWS = 25000;
diff --git a/services/matchSuggestionService.js b/services/matchSuggestionService.cts
similarity index 80%
rename from services/matchSuggestionService.js
rename to services/matchSuggestionService.cts
index 42e6193..cfdff99 100644
--- a/services/matchSuggestionService.js
+++ b/services/matchSuggestionService.cts
@@ -1,19 +1,23 @@
 'use strict';
 
+import type { Db } from '../types/db';
+
 const { getDb } = require('../db/database');
 const { getCycleRange, resolveDueDate } = require('./statusService.cts');
-const { decorateTransaction } = require('./transactionService');
-const { fromCents } = require('../utils/money.mts');
+const { decorateTransaction } = require('./transactionService.cts');
+const { fromCents } = require('../utils/money.mts') as typeof import('../utils/money.mts');
 
-function suggestionError(status, message, code, field = null) {
-  const err = new Error(message);
+type Row = Record<string, any>;
+
+function suggestionError(status: number, message: string, code: string, field: string | null = null): Error {
+  const err = new Error(message) as any;
   err.status = status;
   err.code = code;
   err.field = field;
   return err;
 }
 
-function normalizeId(value, field) {
+function normalizeId(value: unknown, field: string): number {
   const id = typeof value === 'number' ? value : Number(value);
   if (!Number.isSafeInteger(id) || id <= 0) {
     throw suggestionError(400, `${field} must be a positive integer`, 'VALIDATION_ERROR', field);
@@ -21,11 +25,11 @@ function normalizeId(value, field) {
   return id;
 }
 
-function suggestionId(transactionId, billId) {
+function suggestionId(transactionId: any, billId: any): string {
   return `${transactionId}:${billId}`;
 }
 
-function parseSuggestionId(id) {
+function parseSuggestionId(id: unknown): { transactionId: number; billId: number } {
   const match = /^(\d+):(\d+)$/.exec(String(id || '').trim());
   if (!match) {
     throw suggestionError(400, 'Suggestion id must be transactionId:billId', 'VALIDATION_ERROR', 'id');
@@ -36,36 +40,36 @@ function parseSuggestionId(id) {
   };
 }
 
-function textKey(value) {
+function textKey(value: unknown): string {
   return String(value || '')
     .toLowerCase()
     .replace(/[^a-z0-9]+/g, ' ')
     .trim();
 }
 
-function transactionDate(transaction) {
+function transactionDate(transaction: Row): string | null {
   const date = transaction.posted_date || String(transaction.transacted_at || '').slice(0, 10);
   return /^\d{4}-\d{2}-\d{2}$/.test(date) ? date : null;
 }
 
-function dateParts(date) {
+function dateParts(date: string): { year: number; month: number } {
   const [year, month] = String(date).split('-').map(Number);
   return { year, month };
 }
 
-function diffDays(a, b) {
+function diffDays(a: string, b: string): number | null {
   const left = new Date(`${a}T00:00:00Z`).getTime();
   const right = new Date(`${b}T00:00:00Z`).getTime();
   if (!Number.isFinite(left) || !Number.isFinite(right)) return null;
   return Math.abs(Math.round((left - right) / 86400000));
 }
 
-function amountDollars(transaction) {
+function amountDollars(transaction: Row): number {
   const cents = Number(transaction.amount);
   return Number.isFinite(cents) ? Math.abs(cents) / 100 : 0;
 }
 
-function addAmountScore(score, reasons, transaction, bill) {
+function addAmountScore(score: number, reasons: string[], transaction: Row, bill: Row): number {
   const txAmount = amountDollars(transaction);
   const expected = fromCents(bill.expected_amount) || 0;
   if (txAmount <= 0 || expected <= 0) return score;
@@ -91,7 +95,7 @@ function addAmountScore(score, reasons, transaction, bill) {
   return score;
 }
 
-function addDateScore(score, reasons, transaction, bill) {
+function addDateScore(score: number, reasons: string[], transaction: Row, bill: Row): number {
   const postedDate = transactionDate(transaction);
   if (!postedDate) return score;
 
@@ -117,17 +121,17 @@ function addDateScore(score, reasons, transaction, bill) {
 }
 
 // Word-boundary comparison — same logic as billMerchantRuleService.merchantMatches()
-function wordBoundaryIncludes(a, b) {
+function wordBoundaryIncludes(a: string, b: string): boolean {
   if (!a || !b) return false;
   if (a === b) return true;
   try {
-    const esc = s => s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
-    const wb  = s => new RegExp(`(^|\\s)${esc(s)}(\\s|$)`);
+    const esc = (s: string) => s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+    const wb  = (s: string) => new RegExp(`(^|\\s)${esc(s)}(\\s|$)`);
     return wb(b).test(a) || wb(a).test(b);
   } catch { return false; }
 }
 
-function addNameScore(score, reasons, transaction, bill) {
+function addNameScore(score: number, reasons: string[], transaction: Row, bill: Row): number {
   const billName = textKey(bill.name);
   if (!billName) return score;
 
@@ -150,7 +154,7 @@ function addNameScore(score, reasons, transaction, bill) {
   return score;
 }
 
-function addPriorMatchScore(score, reasons, transaction, bill, priorMatchKeys) {
+function addPriorMatchScore(score: number, reasons: string[], transaction: Row, bill: Row, priorMatchKeys: Set<string>): number {
   const payee = textKey(transaction.payee);
   const description = textKey(transaction.description);
   if (
@@ -163,7 +167,7 @@ function addPriorMatchScore(score, reasons, transaction, bill, priorMatchKeys) {
   return score;
 }
 
-function hasPaymentInTransactionCycle(db, bill, transaction) {
+function hasPaymentInTransactionCycle(db: Db, bill: Row, transaction: Row): boolean {
   const postedDate = transactionDate(transaction);
   if (!postedDate) return false;
   const { year, month } = dateParts(postedDate);
@@ -180,8 +184,8 @@ function hasPaymentInTransactionCycle(db, bill, transaction) {
   `).get(bill.id, range.start, range.end);
 }
 
-function loadCandidateTransactions(db, userId, transactionId = null) {
-  const params = [userId];
+function loadCandidateTransactions(db: Db, userId: number, transactionId: number | null = null): any[] {
+  const params: any[] = [userId];
   const where = [
     't.user_id = ?',
     't.ignored = 0',
@@ -215,7 +219,7 @@ function loadCandidateTransactions(db, userId, transactionId = null) {
   `).all(...params).map(decorateTransaction);
 }
 
-function loadBills(db, userId) {
+function loadBills(db: Db, userId: number): Row[] {
   return db.prepare(`
     SELECT b.*, c.name AS category_name
     FROM bills b
@@ -227,17 +231,17 @@ function loadBills(db, userId) {
   `).all(userId);
 }
 
-function loadRejections(db, userId) {
+function loadRejections(db: Db, userId: number): Set<string> {
   const rows = db.prepare(`
     SELECT transaction_id, bill_id
     FROM match_suggestion_rejections
     WHERE user_id = ?
       AND rejected_at > datetime('now', '-90 days')
   `).all(userId);
-  return new Set(rows.map(row => suggestionId(row.transaction_id, row.bill_id)));
+  return new Set(rows.map((row: Row) => suggestionId(row.transaction_id, row.bill_id)));
 }
 
-function loadPriorMatchKeys(db, userId) {
+function loadPriorMatchKeys(db: Db, userId: number): Set<string> {
   const rows = db.prepare(`
     SELECT matched_bill_id, payee, description
     FROM transactions
@@ -246,7 +250,7 @@ function loadPriorMatchKeys(db, userId) {
       AND match_status = 'matched'
       AND ignored = 0
   `).all(userId);
-  const keys = new Set();
+  const keys = new Set<string>();
   for (const row of rows) {
     const payee = textKey(row.payee);
     const description = textKey(row.description);
@@ -256,8 +260,8 @@ function loadPriorMatchKeys(db, userId) {
   return keys;
 }
 
-function scoreSuggestion(transaction, bill, priorMatchKeys) {
-  const reasons = [];
+function scoreSuggestion(transaction: Row, bill: Row, priorMatchKeys: Set<string>): { score: number; reasons: string[] } {
+  const reasons: string[] = [];
   let score = 0;
   score = addAmountScore(score, reasons, transaction, bill);
   score = addDateScore(score, reasons, transaction, bill);
@@ -266,8 +270,8 @@ function scoreSuggestion(transaction, bill, priorMatchKeys) {
   return { score: Math.min(score, 100), reasons };
 }
 
-function listMatchSuggestions(userId, options = {}) {
-  const db = getDb();
+function listMatchSuggestions(userId: number, options: Row = {}): any[] {
+  const db: Db = getDb();
   const rawTransactionId = options.transactionId ?? options.transaction_id;
   const transactionId = rawTransactionId
     ? normalizeId(rawTransactionId, 'transaction_id')
@@ -278,7 +282,7 @@ function listMatchSuggestions(userId, options = {}) {
   const bills = loadBills(db, userId);
   const rejections = loadRejections(db, userId);
   const priorMatchKeys = loadPriorMatchKeys(db, userId);
-  const suggestions = [];
+  const suggestions: any[] = [];
 
   for (const transaction of transactions) {
     for (const bill of bills) {
@@ -312,8 +316,8 @@ function listMatchSuggestions(userId, options = {}) {
     .slice(0, limit);
 }
 
-function rejectMatchSuggestion(userId, id) {
-  const db = getDb();
+function rejectMatchSuggestion(userId: number, id: unknown) {
+  const db: Db = getDb();
   const parsed = parseSuggestionId(id);
 
   const transaction = db.prepare('SELECT id FROM transactions WHERE id = ? AND user_id = ?').get(parsed.transactionId, userId);
@@ -345,8 +349,8 @@ function rejectMatchSuggestion(userId, id) {
 // Called by the background sync worker after each successful source sync.
 // Score of 80+ requires at minimum exact amount + date proximity + name signal,
 // so false-positive risk is low.
-function autoMatchForUser(userId) {
-  const { matchTransactionToBill } = require('./transactionMatchService');
+function autoMatchForUser(userId: number): number {
+  const { matchTransactionToBill } = require('./transactionMatchService.cts');
   const suggestions = listMatchSuggestions(userId, { limit: 50 });
   let matched = 0;
   for (const s of suggestions) {
diff --git a/services/merchantStoreMatchService.js b/services/merchantStoreMatchService.cts
similarity index 80%
rename from services/merchantStoreMatchService.js
rename to services/merchantStoreMatchService.cts
index 33dbb2e..f1e7a46 100644
--- a/services/merchantStoreMatchService.js
+++ b/services/merchantStoreMatchService.cts
@@ -1,27 +1,31 @@
 'use strict';
 
+import type { Db } from '../types/db';
+
 const { categorizeTransaction } = require('./spendingService.cts');
 
+type Row = Record<string, any>;
+
 // Mirrors the pack's match_order_recommendation: regional descriptor variants
 // (most specific — tied to a city/county) are checked first, then online
 // billing descriptors (PAYPAL/STRIPE/APPLE.COM/BILL/etc.), then canonical
 // national merchants as the fallback.
-const ENTRY_KIND_ORDER = {
+const ENTRY_KIND_ORDER: Record<string, number> = {
   regional_descriptor_variant: 0,
   online_billing_descriptor_variant: 1,
   canonical_merchant: 2,
 };
 
-let _entries = null;
+let _entries: any[] | null = null;
 
-function maxPatternLength(patterns) {
+function maxPatternLength(patterns: string[]): number {
   return patterns.reduce((max, p) => Math.max(max, p.length), 0);
 }
 
 // Lazily load and pre-sort all merchant_store_matches rows. Cached for the
 // lifetime of the process — this is static reference data seeded once by the
 // v1.05 migration.
-function loadMerchantMatchEntries(db) {
+function loadMerchantMatchEntries(db: Db): any[] {
   if (_entries) return _entries;
 
   const rows = db.prepare(`
@@ -31,7 +35,7 @@ function loadMerchantMatchEntries(db) {
     FROM merchant_store_matches
   `).all();
 
-  _entries = rows.map(row => ({
+  _entries = rows.map((row: Row) => ({
     ...row,
     match_patterns: JSON.parse(row.match_patterns || '[]'),
     negative_patterns: JSON.parse(row.negative_patterns || '[]'),
@@ -51,7 +55,7 @@ function loadMerchantMatchEntries(db) {
 // Apply the pack's normalization rules: uppercase, "&" -> "AND", strip
 // apostrophes/punctuation, collapse whitespace. match_patterns in the pack
 // are pre-normalized to this same shape (e.g. "THE CHILDREN S PLACE").
-function normalizeForMatch(value) {
+function normalizeForMatch(value: unknown): string {
   return String(value || '')
     .toUpperCase()
     .replace(/&/g, ' AND ')
@@ -63,14 +67,14 @@ function normalizeForMatch(value) {
 
 // Find the best merchant/store match for a raw transaction description.
 // Returns { entry_id, canonical_name, display_name, category, scope, priority } or null.
-function findMerchantMatch(db, description) {
+function findMerchantMatch(db: Db, description: unknown): Row | null {
   const normalized = normalizeForMatch(description);
   if (!normalized) return null;
 
   const entries = loadMerchantMatchEntries(db);
   for (const entry of entries) {
-    if (entry.negative_patterns.some(p => normalized.includes(p))) continue;
-    if (entry.match_patterns.some(p => p && normalized.includes(p))) {
+    if (entry.negative_patterns.some((p: string) => normalized.includes(p))) continue;
+    if (entry.match_patterns.some((p: string) => p && normalized.includes(p))) {
       return {
         entry_id: entry.id,
         canonical_name: entry.canonical_name,
@@ -86,7 +90,7 @@ function findMerchantMatch(db, description) {
 
 // Find-or-create a spending category by name for this user, matching the
 // COLLATE NOCASE convention used by ensureUserDefaultCategories (db/database.js).
-function findOrCreateCategory(db, userId, name) {
+function findOrCreateCategory(db: Db, userId: number, name: string): number | bigint {
   const existing = db.prepare('SELECT id FROM categories WHERE user_id = ? AND name = ? COLLATE NOCASE')
     .get(userId, name);
   if (existing) return existing.id;
@@ -98,12 +102,9 @@ function findOrCreateCategory(db, userId, name) {
 // and categorize them (writing spending_category_rules so future syncs hit
 // the cheaper rule path instead of rescanning the full pack).
 //
-// With { dryRun: true }, computes the same matches without writing anything
-// (no categories created, no transactions updated) — used to preview an
-// auto-categorize run before applying it.
-//
-// Returns { updated: number, categories: [{ name, count }], changes: [{ transaction_id, display_name, category }] }.
-function applyMerchantStoreMatches(db, userId, { dryRun = false } = {}) {
+// With { dryRun: true }, computes the same matches without writing anything.
+// Returns { updated, categories: [{name,count}], changes: [{transaction_id,display_name,category}] }.
+function applyMerchantStoreMatches(db: Db, userId: number, { dryRun = false }: { dryRun?: boolean } = {}) {
   const txRows = db.prepare(`
     SELECT id, payee, description, memo
     FROM transactions
@@ -114,10 +115,10 @@ function applyMerchantStoreMatches(db, userId, { dryRun = false } = {}) {
       AND spending_category_id IS NULL
   `).all(userId);
 
-  if (txRows.length === 0) return { updated: 0, categories: [], changes: [] };
+  if (txRows.length === 0) return { updated: 0, categories: [] as any[], changes: [] as any[] };
 
-  const categoryCounts = new Map(); // category name -> count
-  const changes = [];
+  const categoryCounts = new Map<string, number>(); // category name -> count
+  const changes: any[] = [];
   let updated = 0;
 
   const apply = () => {
diff --git a/services/ofxImportService.js b/services/ofxImportService.js
index de4b7ca..0a3c04b 100644
--- a/services/ofxImportService.js
+++ b/services/ofxImportService.js
@@ -10,7 +10,7 @@
 // so dedupe scope, the import_sessions table, and import_history are identical.
 
 const { getDb } = require('../db/database');
-const { decorateTransaction, ensureManualDataSource } = require('./transactionService');
+const { decorateTransaction, ensureManualDataSource } = require('./transactionService.cts');
 const {
   saveImportSession,
   loadImportSession,
diff --git a/services/snowballService.js b/services/snowballService.cts
similarity index 83%
rename from services/snowballService.js
rename to services/snowballService.cts
index a274a57..2774247 100644
--- a/services/snowballService.js
+++ b/services/snowballService.cts
@@ -1,5 +1,6 @@
+import type { Dollars } from '../utils/money.mts';
 
-const { roundMoney, sumMoney } = require('../utils/money.mts');
+const { roundMoney, sumMoney } = require('../utils/money.mts') as typeof import('../utils/money.mts');
 /**
  * Debt payoff calculators — Snowball and Avalanche methods.
  *
@@ -9,13 +10,36 @@ const { roundMoney, sumMoney } = require('../utils/money.mts');
  * Both share the same month-by-month simulation loop; only the initial order differs.
  */
 
+type Row = Record<string, any>;
+
+interface ActiveDebt {
+  id: any;
+  name: any;
+  balance: number;
+  minPayment: number;
+  monthlyRate: number;
+  payoffMonth: number | null;
+  totalInterest: number;
+}
+interface SkippedDebt { id: any; name: any; reason: string }
+interface DebtProjection {
+  months_to_freedom: number | null;
+  total_interest_paid: number;
+  payoff_date: string | null;
+  payoff_display: string | null;
+  debts: any[];
+  skipped: SkippedDebt[];
+  extra_payment: number;
+  capped: boolean;
+}
+
 // ── Private simulation engine ─────────────────────────────────────────────────
 
-function _simulate(orderedDebts, extraPayment, startDate) {
+function _simulate(orderedDebts: Row[], extraPayment: number, startDate: Date): DebtProjection {
   const extra = Math.max(0, Number(extraPayment) || 0);
 
-  const active  = [];
-  const skipped = [];
+  const active: ActiveDebt[]  = [];
+  const skipped: SkippedDebt[] = [];
 
   for (const d of orderedDebts) {
     const bal = Number(d.current_balance);
@@ -93,12 +117,12 @@ function _simulate(orderedDebts, extraPayment, startDate) {
   const baseYear = startDate.getFullYear();
   const baseMo   = startDate.getMonth();
 
-  function monthLabel(m) {
+  function monthLabel(m: number): string {
     const d = new Date(baseYear, baseMo + m, 1);
     return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}`;
   }
 
-  function monthDisplay(m) {
+  function monthDisplay(m: number): string {
     const d = new Date(baseYear, baseMo + m, 1);
     return d.toLocaleDateString('en-US', { year: 'numeric', month: 'long' });
   }
@@ -140,7 +164,7 @@ function _simulate(orderedDebts, extraPayment, startDate) {
  * Snowball: attack the smallest balance first (fast wins, motivational).
  * Debts must already be in snowball order (sorted by current_balance ASC by the caller).
  */
-function calculateSnowball(debts, extraPayment = 0, startDate = new Date()) {
+function calculateSnowball(debts: Row[], extraPayment = 0, startDate: Date = new Date()): DebtProjection {
   return _simulate(debts, extraPayment, startDate);
 }
 
@@ -148,7 +172,7 @@ function calculateSnowball(debts, extraPayment = 0, startDate = new Date()) {
  * Avalanche: attack the highest interest rate first (minimises total interest paid).
  * Re-sorts debts internally — caller does not need to pre-sort.
  */
-function calculateAvalanche(debts, extraPayment = 0, startDate = new Date()) {
+function calculateAvalanche(debts: Row[], extraPayment = 0, startDate: Date = new Date()): DebtProjection {
   const sorted = [...debts].sort((a, b) => {
     const ra = Number(a.interest_rate) || 0;
     const rb = Number(b.interest_rate) || 0;
@@ -159,7 +183,7 @@ function calculateAvalanche(debts, extraPayment = 0, startDate = new Date()) {
   return _simulate(sorted, extraPayment, startDate);
 }
 
-function round2(n) {
+function round2(n: number): Dollars {
   return roundMoney(n);
 }
 
diff --git a/services/transactionMatchService.js b/services/transactionMatchService.cts
similarity index 82%
rename from services/transactionMatchService.js
rename to services/transactionMatchService.cts
index 25496ba..ecd0d0f 100644
--- a/services/transactionMatchService.js
+++ b/services/transactionMatchService.cts
@@ -1,5 +1,7 @@
 'use strict';
 
+import type { Db } from '../types/db';
+
 const { getDb } = require('../db/database');
 const { computeBalanceDelta, applyBalanceDelta } = require('./billsService');
 const {
@@ -9,22 +11,24 @@ const {
 const {
   decorateTransaction,
   getTransactionForUser,
-} = require('./transactionService');
+} = require('./transactionService.cts');
 const { serializePayment } = require('./paymentValidation.cts');
 const { markMatched, markUnmatched, markIgnored } = require('./transactionMatchState.cts');
 
+type Row = Record<string, any>;
+
 const MATCH_PAYMENT_SOURCE = 'transaction_match';
 const MATCH_PAYMENT_METHOD = 'transaction_match';
 
-function matchError(status, message, code, field = null) {
-  const err = new Error(message);
+function matchError(status: number, message: string, code: string, field: string | null = null): Error {
+  const err = new Error(message) as any;
   err.status = status;
   err.code = code;
   err.field = field;
   return err;
 }
 
-function normalizeId(value, field) {
+function normalizeId(value: unknown, field: string): number {
   const id = typeof value === 'number' ? value : Number(value);
   if (!Number.isSafeInteger(id) || id <= 0) {
     throw matchError(400, `${field} must be a positive integer`, 'VALIDATION_ERROR', field);
@@ -32,7 +36,7 @@ function normalizeId(value, field) {
   return id;
 }
 
-function getOwnedTransaction(db, userId, transactionId) {
+function getOwnedTransaction(db: Db, userId: number, transactionId: unknown): Row {
   const id = normalizeId(transactionId, 'transaction_id');
   const transaction = getTransactionForUser(db, userId, id);
   if (!transaction) {
@@ -41,7 +45,7 @@ function getOwnedTransaction(db, userId, transactionId) {
   return transaction;
 }
 
-function getOwnedBill(db, userId, billId) {
+function getOwnedBill(db: Db, userId: number, billId: unknown): Row {
   const id = normalizeId(billId, 'bill_id');
   const bill = db.prepare(`
     SELECT *
@@ -54,7 +58,7 @@ function getOwnedBill(db, userId, billId) {
   return bill;
 }
 
-function paymentDateForTransaction(transaction) {
+function paymentDateForTransaction(transaction: Row): string {
   const date = transaction.posted_date || String(transaction.transacted_at || '').slice(0, 10);
   if (!/^\d{4}-\d{2}-\d{2}$/.test(date)) {
     throw matchError(
@@ -67,7 +71,7 @@ function paymentDateForTransaction(transaction) {
   return date;
 }
 
-function paymentAmountForTransaction(transaction) {
+function paymentAmountForTransaction(transaction: Row): number {
   const cents = Number(transaction.amount);
   if (!Number.isSafeInteger(cents) || cents === 0) {
     throw matchError(
@@ -80,7 +84,7 @@ function paymentAmountForTransaction(transaction) {
   return Math.round(Math.abs(cents)); // tx.amount and payments.amount are both cents
 }
 
-function getActivePaymentForTransaction(db, userId, transactionId) {
+function getActivePaymentForTransaction(db: Db, userId: number, transactionId: number): Row | undefined {
   return db.prepare(`
     SELECT p.*
     FROM payments p
@@ -94,7 +98,7 @@ function getActivePaymentForTransaction(db, userId, transactionId) {
   `).get(transactionId, userId);
 }
 
-function getPaymentForResponse(db, userId, paymentId) {
+function getPaymentForResponse(db: Db, userId: number, paymentId: number | bigint | null): Row | null {
   if (!paymentId) return null;
   return db.prepare(`
     SELECT p.*
@@ -105,7 +109,7 @@ function getPaymentForResponse(db, userId, paymentId) {
   `).get(paymentId, userId) || null;
 }
 
-function restorePaymentBalance(db, payment) {
+function restorePaymentBalance(db: Db, payment: Row): void {
   if (!payment || payment.balance_delta == null) return;
   const bill = db.prepare('SELECT id, current_balance FROM bills WHERE id = ?').get(payment.bill_id);
   if (bill?.current_balance == null) return;
@@ -122,14 +126,14 @@ function restorePaymentBalance(db, payment) {
   `).run(restored, payment.interest_delta != null ? 1 : 0, bill.id);
 }
 
-function applyPaymentBalance(db, bill, amount) {
+function applyPaymentBalance(db: Db, bill: Row, amount: number): { balance_delta: any; interest_delta: any } {
   const freshBill = db.prepare('SELECT * FROM bills WHERE id = ?').get(bill.id) || bill;
   const balCalc = computeBalanceDelta(freshBill, amount);
   applyBalanceDelta(db, bill.id, balCalc);
   return { balance_delta: balCalc?.balance_delta ?? null, interest_delta: balCalc?.interest_delta ?? null };
 }
 
-function updatePaymentBalanceDeltas(db, paymentId, deltas) {
+function updatePaymentBalanceDeltas(db: Db, paymentId: number | bigint, deltas: { balance_delta: any; interest_delta: any }): void {
   db.prepare(`
     UPDATE payments
     SET balance_delta = ?,
@@ -139,12 +143,12 @@ function updatePaymentBalanceDeltas(db, paymentId, deltas) {
   `).run(deltas.balance_delta, deltas.interest_delta, paymentId);
 }
 
-function buildMatchPaymentNotes(transaction, bill) {
+function buildMatchPaymentNotes(transaction: Row, bill: Row): string {
   const label = transaction.payee || transaction.description || `transaction ${transaction.id}`;
   return `Matched transaction to ${bill.name}: ${label}`.slice(0, 500);
 }
 
-function createOrUpdateMatchPayment(db, userId, transaction, bill) {
+function createOrUpdateMatchPayment(db: Db, userId: number, transaction: Row, bill: Row): number | bigint {
   const amount = paymentAmountForTransaction(transaction);
   const paidDate = paymentDateForTransaction(transaction);
   const notes = buildMatchPaymentNotes(transaction, bill);
@@ -209,7 +213,7 @@ function createOrUpdateMatchPayment(db, userId, transaction, bill) {
   return result.lastInsertRowid;
 }
 
-function unlinkPaymentForTransaction(db, userId, transactionId) {
+function unlinkPaymentForTransaction(db: Db, userId: number, transactionId: number): Row | null {
   const existingPayment = getActivePaymentForTransaction(db, userId, transactionId);
   if (!existingPayment) return null;
 
@@ -232,7 +236,7 @@ function unlinkPaymentForTransaction(db, userId, transactionId) {
   return { ...serializePayment(existingPayment), unlinked: true };
 }
 
-function responseForTransaction(db, userId, transactionId, paymentId = null, extra = {}) {
+function responseForTransaction(db: Db, userId: number, transactionId: number, paymentId: number | bigint | null = null, extra: Row = {}) {
   return {
     success: true,
     transaction: decorateTransaction(getTransactionForUser(db, userId, transactionId)),
@@ -245,8 +249,8 @@ function responseForTransaction(db, userId, transactionId, paymentId = null, ext
 // merchant→bill rule so future synced transactions from the same merchant
 // auto-match. Left false for background auto-matching to avoid compounding
 // a wrong auto-match into a permanent rule.
-function matchTransactionToBill(userId, transactionId, billId, opts = {}) {
-  const db = getDb();
+function matchTransactionToBill(userId: number, transactionId: unknown, billId: unknown, opts: { learnMerchant?: boolean } = {}) {
+  const db: Db = getDb();
   const tx = db.transaction(() => {
     const transaction = getOwnedTransaction(db, userId, transactionId);
     if (transaction.ignored || transaction.match_status === 'ignored') {
@@ -269,8 +273,8 @@ function matchTransactionToBill(userId, transactionId, billId, opts = {}) {
   return tx();
 }
 
-function unmatchTransaction(userId, transactionId) {
-  const db = getDb();
+function unmatchTransaction(userId: number, transactionId: unknown) {
+  const db: Db = getDb();
   const tx = db.transaction(() => {
     const transaction = getOwnedTransaction(db, userId, transactionId);
     const removedPayment = unlinkPaymentForTransaction(db, userId, transaction.id);
@@ -283,8 +287,8 @@ function unmatchTransaction(userId, transactionId) {
   return tx();
 }
 
-function ignoreTransaction(userId, transactionId) {
-  const db = getDb();
+function ignoreTransaction(userId: number, transactionId: unknown) {
+  const db: Db = getDb();
   const tx = db.transaction(() => {
     const transaction = getOwnedTransaction(db, userId, transactionId);
     const removedPayment = unlinkPaymentForTransaction(db, userId, transaction.id);
@@ -297,8 +301,8 @@ function ignoreTransaction(userId, transactionId) {
   return tx();
 }
 
-function unignoreTransaction(userId, transactionId) {
-  const db = getDb();
+function unignoreTransaction(userId: number, transactionId: unknown) {
+  const db: Db = getDb();
   const tx = db.transaction(() => {
     const transaction = getOwnedTransaction(db, userId, transactionId);
 
diff --git a/services/transactionService.js b/services/transactionService.cts
similarity index 85%
rename from services/transactionService.js
rename to services/transactionService.cts
index ccc4768..cad57b2 100644
--- a/services/transactionService.js
+++ b/services/transactionService.cts
@@ -1,20 +1,24 @@
-const SOURCE_TYPE_LABELS = {
+import type { Db } from '../types/db';
+
+type Row = Record<string, any>;
+
+const SOURCE_TYPE_LABELS: Record<string, string> = {
   manual: 'Manual',
   file_import: 'File import',
   provider_sync: 'Provider sync',
 };
 
-function sourceTypeLabel(type) {
-  return SOURCE_TYPE_LABELS[type] || String(type || 'Unknown');
+function sourceTypeLabel(type: unknown): string {
+  return SOURCE_TYPE_LABELS[type as string] || String(type || 'Unknown');
 }
 
-function sourceLabel(source = {}) {
+function sourceLabel(source: Row = {}): string {
   if (source.type === 'manual' || source.provider === 'manual') return source.name || 'Manual Entry';
   if (source.name && source.provider) return `${source.name} (${source.provider})`;
   return source.name || source.provider || sourceTypeLabel(source.type);
 }
 
-function decorateDataSource(row) {
+function decorateDataSource(row: Row | null): Row | null {
   if (!row) return null;
   const safe = { ...row };
   delete safe.encrypted_secret;
@@ -25,7 +29,7 @@ function decorateDataSource(row) {
   };
 }
 
-function decorateTransaction(row) {
+function decorateTransaction(row: Row | null): Row | null {
   if (!row) return null;
   const source = row.data_source_id ? {
     id: row.data_source_id,
@@ -44,7 +48,7 @@ function decorateTransaction(row) {
   };
 }
 
-function ensureManualDataSource(db, userId) {
+function ensureManualDataSource(db: Db, userId: number): Row {
   const existing = db.prepare(`
     SELECT *
     FROM data_sources
@@ -71,7 +75,7 @@ function ensureManualDataSource(db, userId) {
   return db.prepare('SELECT * FROM data_sources WHERE id = ? AND user_id = ?').get(result.lastInsertRowid, userId);
 }
 
-function getTransactionForUser(db, userId, id) {
+function getTransactionForUser(db: Db, userId: number, id: number): Row | undefined {
   return db.prepare(`
     SELECT
       t.id, t.user_id, t.data_source_id, t.account_id, t.provider_transaction_id,
diff --git a/tests/calendarFeedService.test.js b/tests/calendarFeedService.test.js
index 171603d..e66a7ac 100644
--- a/tests/calendarFeedService.test.js
+++ b/tests/calendarFeedService.test.js
@@ -15,7 +15,7 @@ const {
   escapeText,
   foldLine,
   rruleForCycle,
-} = require('../services/calendarFeedService');
+} = require('../services/calendarFeedService.cts');
 const { getDb, closeDb } = require('../db/database');
 
 function createUser(db, username = 'calendar-user') {
diff --git a/tests/snowballMath.test.js b/tests/snowballMath.test.js
index 770649e..87493f2 100644
--- a/tests/snowballMath.test.js
+++ b/tests/snowballMath.test.js
@@ -5,7 +5,7 @@
 const test = require('node:test');
 const assert = require('node:assert/strict');
 
-const { calculateSnowball, calculateAvalanche } = require('../services/snowballService');
+const { calculateSnowball, calculateAvalanche } = require('../services/snowballService.cts');
 const {
   monthlyInterest, monthsToPayoff, amortizationSchedule,
   calculateMinimumOnly, debtAprSnapshot,
diff --git a/tests/transactionMatchService.test.js b/tests/transactionMatchService.test.js
index 1b36703..f07f36b 100644
--- a/tests/transactionMatchService.test.js
+++ b/tests/transactionMatchService.test.js
@@ -8,19 +8,19 @@ const dbPath = path.join(os.tmpdir(), `bill-tracker-transaction-match-test-${pro
 process.env.DB_PATH = dbPath;
 
 const { getDb, closeDb } = require('../db/database');
-const { ensureManualDataSource } = require('../services/transactionService');
+const { ensureManualDataSource } = require('../services/transactionService.cts');
 const { getTracker } = require('../services/trackerService');
 const {
   listMatchSuggestions,
   rejectMatchSuggestion,
   suggestionId,
-} = require('../services/matchSuggestionService');
+} = require('../services/matchSuggestionService.cts');
 const {
   ignoreTransaction,
   matchTransactionToBill,
   unignoreTransaction,
   unmatchTransaction,
-} = require('../services/transactionMatchService');
+} = require('../services/transactionMatchService.cts');
 
 function createUser(db, suffix) {
   return db.prepare(`