By the numbers

A quantitative snapshot of the microsoft/TypeScript codebase.

Data collected on 2026-04-30, against commit f350b52331494b68c90ab02e2b6d0828d2a22a74 on main (TypeScript 6.0.0).

Repo at a glance

Metric	Value
Total commits	36,754
Distinct authors (raw)	922
First commit	2014-07-07
Latest commit on main	2026-04-27
TypeScript source files (src/**.ts)	709
TypeScript source lines	~452,600
Test files (tests/cases/**.ts)	18,876
Diagnostic messages	2,130
Top-level src/ projects	17

Source size by area

xychart-beta horizontal
    title "Lines of TypeScript by directory"
    x-axis ["src/lib (incl. DOM .d.ts)", "src/compiler", "src/testRunner", "src/services", "src/server", "src/harness", "src/jsTyping + typingsInstaller"]
    y-axis "Lines" 0 --> 220000
    bar [73594, 192559, 82061, 65478, 18733, 17650, 1209]

Notes:

• src/lib/ is dominated by the auto-generated dom.generated.d.ts (45,109 lines) and webworker.generated.d.ts (15,590 lines). Excluding those leaves ~13k lines of hand-written lib.*.d.ts.
• src/testRunner/ includes the unit-test sources for the compiler/services. The tests/cases/ and tests/baselines/ directories add tens of thousands more files but are not TypeScript source.

Largest source files

Lines	File	Role
54,434	src/compiler/checker.ts	Type checker
45,109	src/lib/dom.generated.d.ts	Generated DOM declarations
15,590	src/lib/webworker.generated.d.ts	Generated WebWorker declarations
12,447	src/compiler/utilities.ts	Compiler-wide utilities
10,823	src/compiler/parser.ts	Parser
10,670	src/compiler/types.ts	Core type definitions and SyntaxKind
7,542	src/compiler/factory/nodeFactory.ts	AST node factory
6,378	src/compiler/emitter.ts	Emitter
6,173	src/services/completions.ts	Completion provider
5,727	src/server/editorServices.ts	tsserver project graph
5,215	src/harness/fourslashImpl.ts	Fourslash test runtime
5,201	src/compiler/program.ts	Program/Compilation orchestration

checker.ts alone is roughly 12% of all source lines and 28% of src/compiler/.

Activity

xychart-beta horizontal
    title "Commits per calendar year"
    x-axis ["2014", "2015", "2016", "2017", "2018", "2019", "2020", "2021", "2022", "2023", "2024", "2025", "2026"]
    y-axis "Commits" 0 --> 7000
    bar [3328, 6550, 6156, 5121, 5176, 3125, 2140, 1243, 1330, 1305, 916, 280, 84]

Commit volume peaked in 2015–2018 during TypeScript's most active feature-addition era and has trended down ever since. The drop in 2024–2025 reflects the maintenance-mode posture and the work pivoting to microsoft/typescript-go.

2025 monthly commits

Month	Commits
2025-01	40
2025-02	33
2025-03	11
2025-04	12
2025-05	10
2025-06	54
2025-07	20
2025-08	9
2025-09	20
2025-10	31
2025-11	13
2025-12	27

The June 2025 spike is mostly merge work for the 5.9 release branch.

Bot-attributed commits

git log reveals at least 1,233 commits with bot attribution (matched on Co-authored-by:, dependabot[bot], github-actions[bot], Copilot, etc.). That's approximately 3.4% of the project history. Recent windows show a higher share — in 2025, dependabot[bot] and Copilot together accounted for roughly 50 of the 280 commits (~18%). This is a lower bound on AI-assisted work since IDE-integrated tools leave no trace in git history.

Test inventory

Test category	Path	Files
Compiler	tests/cases/compiler/	~13,000
Conformance (organised by language area)	tests/cases/conformance/	~5,800 across 50+ subdirectories
Fourslash (language-service)	tests/cases/fourslash/	~3,500
Project (multi-file project tests)	tests/cases/project/	hundreds
Transpile	tests/cases/transpile/	small
Unit (Mocha)	tests/cases/unittests and src/testRunner/unittests/	hundreds

The corresponding tests/baselines/reference/ directory holds the expected output snapshots for each compiler test. A full run produces ~150,000 baseline files.

TODO / FIXME / HACK comments

grep -E '\b(TODO|FIXME|HACK)\b' over src/ yields 468 occurrences across 111 files. The hottest are:

File	Count
src/compiler/checker.ts	59
src/server/session.ts	34
src/harness/client.ts	23
src/services/services.ts	21
src/compiler/parser.ts	15
src/services/refactors/extractSymbol.ts	13
src/services/completions.ts	13
src/compiler/program.ts	12

Many TODO: GH#NNNN comments link to long-standing GitHub issues.

Dependency footprint

The main package.json has 0 runtime dependencies — typescript ships its own bundle. Dev dependencies number ~40 and include @dprint/formatter, @octokit/rest, chai, chokidar, dprint, esbuild, eslint 10, glob, hereby, knip, mocha, playwright, source-map-support, tslib, the typescript-eslint family, and miscellaneous Azure-DevOps utilities. See reference/dependencies.

Source-file vs test-file ratio

The ratio of test files to source files is roughly 27 : 1 (18,876 : 709). For a compiler that aspires to TC39-tracking conformance and to backwards compatibility with a decade of user code, that is a feature, not an indictment.