diff --git a/.cherry.cjs b/.cherry.cjs
index c4439dbe..cabde7d5 100644
--- a/.cherry.cjs
+++ b/.cherry.cjs
@@ -15,15 +15,5 @@ module.exports = {
       name: 'TODO',
       pattern: /TODO/,
     },
-    {
-      name: '[TS Migration] TS lines of code',
-      include: TS_FILES,
-      groupByFile: true,
-    },
-    {
-      name: '[TS Migration] JS lines of code',
-      include: JS_FILES,
-      groupByFile: true,
-    },
   ],
 }
diff --git a/.github/workflows/cherry_diff.yml b/.github/workflows/cherry_diff.yml
index 66aa4005..bbae924c 100644
--- a/.github/workflows/cherry_diff.yml
+++ b/.github/workflows/cherry_diff.yml
@@ -19,4 +19,4 @@ jobs:
       - name: Raise if new JavaScript code is added
         # This command will fail if the number of lines of code in JavaScript files has increased
         # in the current branch compared to the base branch, encouraging developers to contribute to migrating to TS.
-        run: npm run cherry -- diff --metric='TODO' --error-if-increase --quiet
+        run: npm run cherry -- diff --metric='[loc] JavaScript' --error-if-increase --quiet
diff --git a/bin/commands/backfill.js b/bin/commands/backfill.ts
similarity index 92%
rename from bin/commands/backfill.js
rename to bin/commands/backfill.ts
index e12f5600..148788f8 100755
--- a/bin/commands/backfill.js
+++ b/bin/commands/backfill.ts
@@ -9,6 +9,7 @@ import { getConfiguration } from '../../src/configuration.js'
 import { getFiles } from '../../src/files.js'
 import { panic } from '../../src/error.js'
 
+// @ts-expect-error TODO: properly type this
 export default function (program) {
   program
     .command('backfill')
@@ -17,11 +18,14 @@ export default function (program) {
     .option('--until <until>', 'the date at which the backfill will stop as yyyy-mm-dd (defaults to today)')
     .option('--interval <interval>', 'the number of days between backfills (defaults to 30)')
     .option('--quiet', 'reduce output to a minimum')
+    // @ts-expect-error TODO: properly type this
     .action(async (options) => {
       const since = options.since ? new Date(options.since) : substractDays(new Date(), 90)
       const until = options.until ? new Date(options.until) : new Date()
       const interval = options.interval ? parseInt(options.interval) : 30
+      // @ts-expect-error TODO: properly type this
       if (isNaN(since)) panic('Invalid since date')
+      // @ts-expect-error TODO: properly type this
       if (isNaN(until)) panic('Invalid until date')
       if (since > until) panic('The since date must be before the until date')
       const initialBranch = await git.branchName()
@@ -42,11 +46,10 @@ export default function (program) {
 
           await git.checkout(sha)
 
-          const files = await getFiles()
           const codeOwners = new Codeowners()
           const occurrences = await findOccurrences({
             configuration,
-            files,
+            filePaths: await getFiles(),
             codeOwners,
             quiet: options.quiet,
           })
diff --git a/bin/commands/diff.js b/bin/commands/diff.js
index e0030683..d71eb6ee 100755
--- a/bin/commands/diff.js
+++ b/bin/commands/diff.js
@@ -35,7 +35,7 @@ export default function (program) {
       // Start by calculating the occurrences for the current branch
       const currentOccurrences = await findOccurrences({
         configuration,
-        files: await getFiles(),
+        filePaths: await getFiles(),
         metricNames,
         codeOwners: new Codeowners(),
         quiet: options.quiet,
@@ -49,7 +49,7 @@ export default function (program) {
         await git.checkout(baseBranchCommit)
         previousOccurrences = await findOccurrences({
           configuration,
-          files: await getFiles(),
+          filePaths: await getFiles(),
           metricNames,
           codeOwners: new Codeowners(),
           quiet: options.quiet,
diff --git a/bin/commands/push.js b/bin/commands/push.js
index 7459d5bb..6814343c 100755
--- a/bin/commands/push.js
+++ b/bin/commands/push.js
@@ -40,7 +40,7 @@ export default function (program) {
         await git.checkout(`${sha}~`)
         const previousOccurrences = await findOccurrences({
           configuration,
-          files: await getFiles(),
+          filePaths: await getFiles(),
           codeOwners: new Codeowners(),
           quiet: options.quiet,
         })
diff --git a/bin/commands/run.js b/bin/commands/run.js
index 5ef22d2b..3a63190c 100755
--- a/bin/commands/run.js
+++ b/bin/commands/run.js
@@ -32,11 +32,11 @@ export default function (program) {
       const owners = options.owner
       const quiet = options.quiet
 
-      const files = owners ? await getFiles(owners, codeOwners) : await getFiles()
+      const filePaths = owners ? await getFiles(owners, codeOwners) : await getFiles()
 
       const occurrences = await findOccurrences({
         configuration,
-        files,
+        filePaths,
         metricNames: options.metric,
         codeOwners,
         quiet,
diff --git a/bin/helpers.js b/bin/helpers.ts
similarity index 74%
rename from bin/helpers.js
rename to bin/helpers.ts
index aa888c9c..e6fbcd76 100755
--- a/bin/helpers.js
+++ b/bin/helpers.ts
@@ -1,3 +1,5 @@
+import { Contribution, EvalMetric, Metric, Occurrence } from '../src/types.js'
+
 import Spinnies from 'spinnies'
 import _ from 'lodash'
 import axios from 'axios'
@@ -11,7 +13,7 @@ export const API_BASE_URL = process.env.API_URL ?? 'https://www.cherrypush.com/a
 
 export const UPLOAD_BATCH_SIZE = 1000
 
-export const countByMetric = (occurrences) =>
+export const countByMetric = (occurrences: Occurrence[]) =>
   _(occurrences)
     .groupBy('metricName')
     .mapValues((occurrences) =>
@@ -19,10 +21,12 @@ export const countByMetric = (occurrences) =>
     )
     .value()
 
-const handleApiError = async (callback) => {
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+const handleApiError = async (callback: any) => {
   try {
     return await callback()
-  } catch (error) {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  } catch (error: any) {
     if (error.response)
       throw new Error(
         `❌ Error while calling cherrypush.com API ${error.response.status}: ${
@@ -33,7 +37,7 @@ const handleApiError = async (callback) => {
   }
 }
 
-export const buildMetricsPayload = (occurrences) =>
+export const buildMetricsPayload = (occurrences: Occurrence[]) =>
   _(occurrences)
     .groupBy('metricName')
     .mapValues((occurrences, metricName) => ({
@@ -44,7 +48,15 @@ export const buildMetricsPayload = (occurrences) =>
     .flatten()
     .value()
 
-export const uploadContributions = async (apiKey, projectName, authorName, authorEmail, sha, date, contributions) =>
+export const uploadContributions = async (
+  apiKey: string,
+  projectName: string,
+  authorName: string,
+  authorEmail: string,
+  sha: string,
+  date: Date,
+  contributions: Contribution[]
+) =>
   handleApiError(() =>
     axios
       .post(
@@ -55,7 +67,14 @@ export const uploadContributions = async (apiKey, projectName, authorName, autho
       .then(({ data }) => data)
   )
 
-const buildContributionsPayload = (projectName, authorName, authorEmail, sha, date, contributions) => ({
+const buildContributionsPayload = (
+  projectName: string,
+  authorName: string,
+  authorEmail: string,
+  sha: string,
+  date: Date,
+  contributions: Contribution[]
+) => ({
   project_name: projectName,
   author_name: authorName,
   author_email: authorEmail,
@@ -67,7 +86,7 @@ const buildContributionsPayload = (projectName, authorName, authorEmail, sha, da
   })),
 })
 
-export const upload = async (apiKey, projectName, date, occurrences) => {
+export const upload = async (apiKey: string, projectName: string, date: Date, occurrences: Occurrence[]) => {
   if (!projectName) panic('specify a project_name in your cherry.js configuration file before pushing metrics')
 
   const uuid = await v4()
@@ -101,7 +120,8 @@ export const upload = async (apiKey, projectName, date, occurrences) => {
             })
           )
       )
-    } catch (error) {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    } catch (error: any) {
       spinnies.fail('batches', {
         text: `Batch ${index + 1} out of ${occurrencesBatches.length}: ${error.message}`,
       })
@@ -109,7 +129,19 @@ export const upload = async (apiKey, projectName, date, occurrences) => {
   }
 }
 
-const buildPushPayload = ({ apiKey, projectName, uuid, date, occurrences }) => ({
+const buildPushPayload = ({
+  apiKey,
+  projectName,
+  uuid,
+  date,
+  occurrences,
+}: {
+  apiKey: string
+  projectName: string
+  uuid: string
+  date: Date
+  occurrences: Occurrence[]
+}) => ({
   api_key: apiKey,
   project_name: projectName,
   date: date.toISOString(),
@@ -117,7 +149,7 @@ const buildPushPayload = ({ apiKey, projectName, uuid, date, occurrences }) => (
   metrics: buildMetricsPayload(occurrences),
 })
 
-export const buildSarifPayload = (projectName, branch, sha, occurrences) => {
+export const buildSarifPayload = (projectName: string, branch: string, sha: string, occurrences: Occurrence[]) => {
   const rules = _(occurrences)
     .groupBy('metricName')
     .map((occurrences) => ({
@@ -168,7 +200,7 @@ export const buildSarifPayload = (projectName, branch, sha, occurrences) => {
   }
 }
 
-export const buildSonarGenericImportPayload = (occurrences) => ({
+export const buildSonarGenericImportPayload = (occurrences: Occurrence[]) => ({
   issues: occurrences.map((occurrence) => ({
     engineId: 'cherry',
     ruleId: occurrence.metricName,
@@ -184,4 +216,8 @@ export const buildSonarGenericImportPayload = (occurrences) => ({
   })),
 })
 
-export const sortObject = (object) => _(object).toPairs().sortBy(0).fromPairs().value()
+export const sortObject = (object: object) => _(object).toPairs().sortBy(0).fromPairs().value()
+
+export function isEvalMetric(metric: Metric): metric is EvalMetric {
+  return 'eval' in metric
+}
diff --git a/package-lock.json b/package-lock.json
index b6c713ba..bda34474 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -28,6 +28,9 @@
         "cherry": "dist/bin/cherry.js"
       },
       "devDependencies": {
+        "@types/lodash": "^4.17.7",
+        "@types/spinnies": "^0.5.3",
+        "@types/uuid": "^10.0.0",
         "@typescript-eslint/eslint-plugin": "8.x.x",
         "@typescript-eslint/parser": "8.x.x",
         "eslint": "^8.54.0",
@@ -1009,6 +1012,12 @@
       "integrity": "sha512-/kYRxGDLWzHOB7q+wtSUQlFrtcdUccpfy+X+9iMBpHK8QLLhx2wIPYuS5DYtR9Wa/YlZAbIovy7qVdB1Aq6Lyw==",
       "dev": true
     },
+    "node_modules/@types/lodash": {
+      "version": "4.17.7",
+      "resolved": "https://registry.npmjs.org/@types/lodash/-/lodash-4.17.7.tgz",
+      "integrity": "sha512-8wTvZawATi/lsmNu10/j2hk1KEP0IvjubqPE3cu1Xz7xfXXt5oCq3SNUz4fMIP4XGF9Ky+Ue2tBA3hcS7LSBlA==",
+      "dev": true
+    },
     "node_modules/@types/node": {
       "version": "22.5.4",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-22.5.4.tgz",
@@ -1020,6 +1029,18 @@
         "undici-types": "~6.19.2"
       }
     },
+    "node_modules/@types/spinnies": {
+      "version": "0.5.3",
+      "resolved": "https://registry.npmjs.org/@types/spinnies/-/spinnies-0.5.3.tgz",
+      "integrity": "sha512-HYrOubG2TVgRQRKcW1HJ/1eJIIBpLqDoJo551McJgWdO8xzxnaxu/bPKdqC/7okoEy4ZZjy3I4/DwK1sz2OCog==",
+      "dev": true
+    },
+    "node_modules/@types/uuid": {
+      "version": "10.0.0",
+      "resolved": "https://registry.npmjs.org/@types/uuid/-/uuid-10.0.0.tgz",
+      "integrity": "sha512-7gqG38EyHgyP1S+7+xomFtL+ZNHcKv6DwNaCZmJmo1vgMugyF3TCnXVg4t1uk89mLNwnLtnY3TpOpCOyp1/xHQ==",
+      "dev": true
+    },
     "node_modules/@typescript-eslint/eslint-plugin": {
       "version": "8.5.0",
       "resolved": "https://registry.npmjs.org/@typescript-eslint/eslint-plugin/-/eslint-plugin-8.5.0.tgz",
diff --git a/package.json b/package.json
index ea34be99..08f22cb4 100644
--- a/package.json
+++ b/package.json
@@ -20,6 +20,7 @@
     "test": "sh test/fixtures/setup.sh && vitest run",
     "test:setup": "sh test/fixtures/setup.sh",
     "test:cleanup": "sh test/fixtures/cleanup.sh",
+    "type-check": "tsc --noEmit",
     "format": "prettier --write ."
   },
   "repository": {
@@ -53,6 +54,9 @@
     "uuid": "^9.0.1"
   },
   "devDependencies": {
+    "@types/lodash": "^4.17.7",
+    "@types/spinnies": "^0.5.3",
+    "@types/uuid": "^10.0.0",
     "@typescript-eslint/eslint-plugin": "8.x.x",
     "@typescript-eslint/parser": "8.x.x",
     "eslint": "^8.54.0",
@@ -60,9 +64,9 @@
     "husky": "^9.0.11",
     "lint-staged": "^15.2.10",
     "prettier": "^3.3.3",
+    "tsx": "^4.19.0",
     "typescript": "5.5.4",
-    "vitest": "^2.0.5",
-    "tsx": "^4.19.0"
+    "vitest": "^2.0.5"
   },
   "lint-staged": {
     "*": "prettier --ignore-unknown --write",
diff --git a/src/contributions.js b/src/contributions.ts
similarity index 68%
rename from src/contributions.js
rename to src/contributions.ts
index 704b2123..52f241fa 100644
--- a/src/contributions.js
+++ b/src/contributions.ts
@@ -1,16 +1,18 @@
+import { Contribution, Occurrence } from './types.js'
+
 import _ from 'lodash'
 
-const toCountByMetricName = (occurrences) =>
+const toCountByMetricName = (occurrences: Occurrence[]) =>
   _.mapValues(_.groupBy(occurrences, 'metricName'), (occurrences) =>
     _.sum(occurrences.map((occurrence) => occurrence.value || 1))
   )
 
-export const computeContributions = (occurrences, previousOccurrences) => {
+export const computeContributions = (occurrences: Occurrence[], previousOccurrences: Occurrence[]) => {
   const counts = toCountByMetricName(occurrences)
   const previousCounts = toCountByMetricName(previousOccurrences)
 
   const metrics = _.uniq(Object.keys(counts).concat(Object.keys(previousCounts)))
-  const contributions = []
+  const contributions: Contribution[] = []
   metrics.forEach((metric) => {
     const diff = (counts[metric] || 0) - (previousCounts[metric] || 0)
     if (diff !== 0) contributions.push({ metricName: metric, diff })
diff --git a/src/date.js b/src/date.ts
similarity index 51%
rename from src/date.js
rename to src/date.ts
index cff0627b..50921bf8 100644
--- a/src/date.js
+++ b/src/date.ts
@@ -1,14 +1,18 @@
-export const toISODate = (date) => date.toISOString().split('T')[0]
-export const substractDays = (date, count) => {
+export const toISODate = (date: Date) => date.toISOString().split('T')[0]
+
+export const substractDays = (date: Date, count: number) => {
   date.setDate(date.getDate() - count)
   return date
 }
-export const addDays = (date, count) => {
+
+export const addDays = (date: Date, count: number) => {
   date.setDate(date.getDate() + count)
   return date
 }
-export const firstDayOfMonth = (date) => new Date(Date.UTC(date.getFullYear(), date.getMonth(), 1))
-export const nextMonth = (originalDate) => {
+
+export const firstDayOfMonth = (date: Date) => new Date(Date.UTC(date.getFullYear(), date.getMonth(), 1))
+
+export const nextMonth = (originalDate: Date) => {
   const date = firstDayOfMonth(originalDate) // Avoid returning 1 for getMonth() when day is 31
   const [year, month] = date.getMonth() < 11 ? [date.getFullYear(), date.getMonth() + 1] : [date.getFullYear() + 1, 0]
 
diff --git a/src/files.js b/src/files.js
index 5c85641b..0d57f63e 100644
--- a/src/files.js
+++ b/src/files.js
@@ -1,22 +1,23 @@
-import { promises as fs } from 'fs'
-import intersection from 'lodash/intersection.js'
 import * as git from './git.js'
 
-class File {
-  constructor(path) {
-    this.path = path
-  }
+import { promises as fs } from 'fs'
+import intersection from 'lodash/intersection.js'
 
-  async readLines() {
-    try {
-      return Buffer.from(await fs.readFile(this.path))
-        .toString()
-        .split(/\r\n|\r|\n/)
-    } catch (error) {
-      if (error.code === 'ENOENT') return []
-      if (error.code === 'EISDIR') return []
-      throw error
-    }
+/**
+ * Reads the lines from a file at a given path.
+ *
+ * @param {string} path - The path to the file.
+ * @returns {Promise<string[]>} A promise that resolves to an array of lines in the file, or an empty array if the file doesn't exist or is a directory.
+ */
+export async function readLines(path) {
+  try {
+    const data = await fs.readFile(path)
+    return Buffer.from(data)
+      .toString()
+      .split(/\r\n|\r|\n/)
+  } catch (error) {
+    if (error.code === 'ENOENT' || error.code === 'EISDIR') return []
+    throw error
   }
 }
 
@@ -25,5 +26,5 @@ export const getFiles = async (owners, codeOwners) => {
   let selectedPaths = allPaths
   if (owners) selectedPaths = intersection(codeOwners.getFiles(owners), selectedPaths)
 
-  return selectedPaths.map((path) => new File(path))
+  return selectedPaths
 }
diff --git a/src/git.js b/src/git.ts
similarity index 78%
rename from src/git.js
rename to src/git.ts
index e994de3a..3fc90038 100644
--- a/src/git.js
+++ b/src/git.ts
@@ -2,7 +2,7 @@ import { CONFIG_FILE_LOCAL_PATHS } from './configuration.js'
 import sh from './sh.js'
 import { toISODate } from './date.js'
 
-export const git = async (cmd) => {
+export const git = async (cmd: string): Promise<string[]> => {
   const { stdout } = await sh(`git ${cmd}`)
   return stdout.toString().split('\n').filter(Boolean)
 }
@@ -30,7 +30,7 @@ export const getRemoteUrl = async () => {
  * Guesses the project name based on the remote URL of the git repository.
  * If the remote URL is not found, returns an empty string.
  */
-export const guessProjectName = (remoteUrl) => {
+export const guessProjectName = (remoteUrl: string) => {
   if (!remoteUrl) return null
 
   // Handle https remotes, such as in https://github.com/cherrypush/cherry-cli.git
@@ -53,19 +53,19 @@ export const getDefaultBranchName = async () => {
   return defaultBranch.replace('origin/', '').trim()
 }
 
-export const getMergeBase = async (currentBranchName, defaultBranchName) =>
+export const getMergeBase = async (currentBranchName: string, defaultBranchName: string) =>
   (await git(`merge-base ${currentBranchName} origin/${defaultBranchName}`)).toString().trim()
 
-export const authorName = async (sha) => (await git(`show ${sha} --format=%an --no-patch`))[0]
+export const authorName = async (sha: string) => (await git(`show ${sha} --format=%an --no-patch`))[0]
 
-export const authorEmail = async (sha) => (await git(`show ${sha} --format=%ae --no-patch`))[0]
+export const authorEmail = async (sha: string) => (await git(`show ${sha} --format=%ae --no-patch`))[0]
 
-export const commitDate = async (sha) => new Date((await git(`show -s --format=%ci ${sha}`))[0])
+export const commitDate = async (sha: string) => new Date((await git(`show -s --format=%ci ${sha}`))[0])
 
-export const commitShaAt = async (date, branch) =>
+export const commitShaAt = async (date: Date, branch: string) =>
   (await git(`rev-list --reverse --after=${toISODate(date)} ${branch}`))[0]
 
-export const checkout = async (sha) => {
+export const checkout = async (sha: string) => {
   console.log(`Checking out ${sha}`)
   await git(`checkout ${sha}`)
 }
diff --git a/src/helpers/timer.ts b/src/helpers/timer.ts
index c8814932..8285f07f 100644
--- a/src/helpers/timer.ts
+++ b/src/helpers/timer.ts
@@ -4,10 +4,6 @@ const timers: Record<string, number> = {}
 
 /**
  * Executes a provided function block and measures its execution time.
- * Logs a message if the execution time exceeds 2 seconds.
- *
- * @param {Function} codeBlock - The block of code to execute.
- * @returns {*} The result of the executed code block.
  */
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 export async function executeWithTiming(codeBlock: any, identifier: string) {
diff --git a/src/occurrences.js b/src/occurrences.ts
similarity index 68%
rename from src/occurrences.js
rename to src/occurrences.ts
index cfbda86e..d087370b 100644
--- a/src/occurrences.js
+++ b/src/occurrences.ts
@@ -1,9 +1,11 @@
+import { Configuration, EvalMetric, Metric, Occurrence, PatternMetric, PluginName, Plugins } from './types.js'
 import { executeWithTiming, warnsAboutLongRunningTasks } from './helpers/timer.js'
 
 import Spinnies from 'spinnies'
 import _ from 'lodash'
 import { buildPermalink } from './permalink.js'
 import eslint from './plugins/eslint.js'
+import { isEvalMetric } from '../bin/helpers.js'
 import jsCircularDependencies from './plugins/js_circular_dependencies.js'
 import jsUnimported from './plugins/js_unimported.js'
 import loc from './plugins/loc.js'
@@ -11,6 +13,7 @@ import minimatch from 'minimatch'
 import npmOutdated from './plugins/npm_outdated.js'
 import pLimit from 'p-limit'
 import { panic } from './error.js'
+import { readLines } from './files.js'
 import rubocop from './plugins/rubocop.js'
 import yarnOutdated from './plugins/yarn_outdated.js'
 
@@ -26,8 +29,9 @@ const PLUGINS = {
   yarnOutdated,
 }
 
-const minimatchCache = {}
-const matchPattern = (path, patternOrPatterns) => {
+const minimatchCache: Record<string, boolean> = {}
+
+const matchPattern = (path: string, patternOrPatterns: string | string[]) => {
   const patterns = Array.isArray(patternOrPatterns) ? patternOrPatterns : [patternOrPatterns]
 
   return patterns.some((pattern) => {
@@ -38,28 +42,31 @@ const matchPattern = (path, patternOrPatterns) => {
   })
 }
 
-const findFileOccurences = async (file, metrics) => {
+const findFileOccurences = async (filePath: string, metrics: PatternMetric[]) => {
   const relevantMetrics = metrics.filter((metric) => {
-    const pathIncluded = metric.include ? matchPattern(file.path, metric.include) : true
-    const pathExcluded = metric.exclude ? matchPattern(file.path, metric.exclude) : false
+    const pathIncluded = metric.include ? matchPattern(filePath, metric.include) : true
+    const pathExcluded = metric.exclude ? matchPattern(filePath, metric.exclude) : false
     return pathIncluded && !pathExcluded
   })
   if (!relevantMetrics.length) return []
 
-  const occurrencesByMetric = {}
-  const lines = await file.readLines()
+  const occurrencesByMetric: Record<string, { path: string; lineNumber: number }[]> = {}
+  const lines = await readLines(filePath)
   lines.forEach((line, lineIndex) => {
     relevantMetrics.forEach((metric) => {
+      // @ts-expect-error TODO: check if we can pass an empty string instead of undefined or skip this step entirely if no pattern was provided
       if (!line.match(metric.pattern)) return
       occurrencesByMetric[metric.name] ||= []
       occurrencesByMetric[metric.name].push({
-        path: file.path,
+        path: filePath,
         lineNumber: lineIndex + 1,
       })
     })
   })
 
+  // @ts-expect-error TODO: properly type this
   return Object.entries(occurrencesByMetric).flatMap(([metricName, occurrences]) => {
+    // @ts-expect-error TODO: properly type this
     const groupByFile = metrics.find((metric) => metric.name === metricName).groupByFile
 
     return groupByFile
@@ -83,7 +90,7 @@ const findFileOccurences = async (file, metrics) => {
   })
 }
 
-const matchPatterns = (files, metrics, quiet) => {
+const matchPatterns = async (files: string[], metrics: PatternMetric[], quiet: boolean): Promise<Occurrence[]> => {
   if (!files.length || !metrics.length) return []
 
   if (!quiet) spinnies.add('patterns', { text: 'Matching patterns...', indent: 2 })
@@ -100,7 +107,8 @@ const matchPatterns = (files, metrics, quiet) => {
   return promise
 }
 
-const runEvals = (metrics, codeOwners, quiet) => {
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+const runEvals = async (metrics: EvalMetric[], codeOwners: any, quiet: boolean): Promise<Occurrence[][]> => {
   if (!metrics.length) return []
 
   if (!quiet) spinnies.add('evals', { text: 'Running eval()...', indent: 2 })
@@ -114,65 +122,84 @@ const runEvals = (metrics, codeOwners, quiet) => {
         })
       }
 
-      const occurrences = await executeWithTiming(
+      // TODO: properly type executeWithTiming and remove the cast
+      const occurrences = (await executeWithTiming(
         async () => await metric.eval({ codeOwners }),
         `Metric '${metric.name}'`
-      )
-      const result = occurrences.map((occurrence) => ({ ...occurrence, metricName: metric.name }))
+      )) as Occurrence[]
+
+      const result = occurrences.map((occurrence) => ({ ...occurrence, metricName: metric.name }) as Occurrence)
 
       if (!quiet) spinnies.succeed(`metric_${metric.name}`, { text: metric.name })
       return result
     })
   )
+
   if (!quiet) promise.then(() => spinnies.succeed('evals', { text: 'Running eval()' }))
 
   return promise
 }
 
-const runPlugins = async (plugins = {}, quiet) => {
+const runPlugins = async (plugins: Plugins = {}, quiet: boolean): Promise<Occurrence[][]> => {
   if (typeof plugins !== 'object' || plugins === null) panic('Plugins should be an object')
   if (!Object.keys(plugins).length) return []
 
   if (!quiet) spinnies.add('plugins', { text: 'Running plugins...', indent: 2 })
+
   const promise = Promise.all(
     Object.entries(plugins).map(async ([name, options]) => {
-      const plugin = PLUGINS[name]
+      const plugin = PLUGINS[name as PluginName]
       if (!plugin) panic(`Unsupported '${name}' plugin\nExpected one of: ${Object.keys(PLUGINS).join(', ')}`)
       if (!quiet) spinnies.add(`plugin_${name}`, { text: `${name}...`, indent: 4 })
+      // @ts-expect-error TODO: properly type plugin options
       const result = executeWithTiming(async () => await plugin.run(options), `Plugin '${name}'`)
       if (!quiet) spinnies.succeed(`plugin_${name}`, { text: name })
       return result
     })
   )
+
   if (!quiet) promise.then(() => spinnies.succeed('plugins', { text: 'Running plugin' }))
 
   return promise
 }
 
-export const emptyMetric = (metricName) => ({
+export const emptyMetric = (metricName: string) => ({
   metricName,
   text: 'No occurrences',
   value: 0,
 })
 
-const withEmptyMetrics = (occurrences, metrics = []) => {
-  const occurrencesByMetric = _.groupBy(occurrences, 'metricName')
-  const allMetricNames = _.uniq(metrics.map((metric) => metric.name).concat(Object.keys(occurrencesByMetric)))
+const withEmptyMetrics = (occurrences: Occurrence[], metrics: Metric[] = []) => {
+  const occurrencesByMetric: Record<string, Occurrence[]> = _.groupBy(occurrences, 'metricName')
+  const allMetricNames: string[] = _.uniq(metrics.map((metric) => metric.name).concat(Object.keys(occurrencesByMetric)))
   return allMetricNames.map((metricName) => occurrencesByMetric[metricName] || [emptyMetric(metricName)]).flat()
 }
 
-export const findOccurrences = async ({ configuration, files, metricNames, codeOwners, quiet }) => {
+export const findOccurrences = async ({
+  configuration,
+  filePaths,
+  metricNames,
+  codeOwners,
+  quiet,
+}: {
+  configuration: Configuration
+  filePaths: string[]
+  metricNames?: string[]
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  codeOwners: any
+  quiet: boolean
+}) => {
   let metrics = configuration.metrics
   const { project_name: projectName, permalink } = configuration
 
   // Prevent running all metrics if a subset is provided
   if (metricNames) metrics = metrics.filter(({ name }) => metricNames.includes(name))
 
-  // Separate metrics into eval and file metrics
-  const [evalMetrics, fileMetrics] = _.partition(metrics, (metric) => metric.eval)
+  // Separate metrics into eval and pattern metrics
+  const [evalMetrics, patternMetrics] = _.partition(metrics, isEvalMetric)
 
   const result = await Promise.all([
-    matchPatterns(files, fileMetrics, quiet),
+    matchPatterns(filePaths, patternMetrics, quiet),
     runEvals(evalMetrics, codeOwners, quiet),
     runPlugins(configuration.plugins, quiet),
   ])
diff --git a/src/sh.js b/src/sh.ts
similarity index 77%
rename from src/sh.js
rename to src/sh.ts
index b42380bc..6d29f5ed 100644
--- a/src/sh.js
+++ b/src/sh.ts
@@ -2,7 +2,7 @@ import child_process from 'child_process'
 import { debug } from './log.js'
 
 // From https://stackoverflow.com/a/68958420/9847645, to avoid 200Kb limit causing ENOBUFS errors for large output
-const sh = (cmd, { throwOnError = true } = {}) =>
+const sh = (cmd: string, { throwOnError = true } = {}): Promise<{ stderr: string; stdout: string }> =>
   new Promise((resolve, reject) => {
     debug('#', cmd)
     const [command, ...args] = cmd.split(/\s+/)
@@ -14,7 +14,7 @@ const sh = (cmd, { throwOnError = true } = {}) =>
     spawnedProcess.stdout.on('data', (chunk) => (stdout += chunk.toString()))
     spawnedProcess.stderr.on('data', (chunk) => (stderr += chunk.toString()))
     spawnedProcess.on('close', (code) => {
-      if (throwOnError && code > 0) return reject(new Error(`${stderr} (Failed Instruction: ${cmd})`))
+      if (throwOnError && code && code > 0) return reject(new Error(`${stderr} (Failed Instruction: ${cmd})`))
       debug(stdout)
       resolve({ stderr, stdout })
     })
diff --git a/src/types.ts b/src/types.ts
new file mode 100644
index 00000000..aaebcafe
--- /dev/null
+++ b/src/types.ts
@@ -0,0 +1,42 @@
+export type Occurrence = {
+  metricName: string
+  filePath?: string // TODO: it's weird that filePath is optional here, let's review this
+  text: string
+  value: number
+  lineNumber?: number
+  url?: string
+  owners?: string[]
+}
+
+export type Contribution = {
+  metricName: string
+  diff: number
+}
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+type Codeowners = any
+
+export type EvalMetric = {
+  name: string
+  eval: (options: { codeOwners: Codeowners }) => Promise<Occurrence[]>
+}
+
+export type PatternMetric = {
+  name: string
+  pattern?: RegExp
+  include?: string | string[]
+  exclude?: string | string[]
+  groupByFile?: boolean
+}
+
+export type Metric = EvalMetric | PatternMetric
+
+export type PluginName = 'loc' | 'jsCircularDependencies' | 'eslint'
+export type Plugins = Partial<Record<PluginName, object>>
+
+export type Configuration = {
+  project_name: string
+  permalink: () => string
+  metrics: Metric[]
+  plugins?: Plugins
+}