JS→TS migration tools 2026
The best JS→TS migration tools in 2026,
honestly compared.
We migrate code for a living, so we compared every serious way to get from JavaScript to TypeScript (free OSS codemods, AI editors, autonomous agents, enterprise platforms, and Refactyl) on the one metric that actually matters: does the result compile, and does it do it without drowning your codebase in `any`?
Why most tool roundups miss the point
Most “best JS→TS migration tools” lists are affiliate roundups written by people who've never run one. This one isn't. We publish a reproducible benchmark on 5 real OSS repos, we name our competitors, and we use a dual metric (errors fixed and `any` density) because any tool hits “zero errors” by typing everything as any.
The second axis is the anti-gaming axis. You cannot have both zero errors and low `any`-density without actually solving the types. That's the only metric a production migration should be judged on, and it's the one almost nobody measures.
All tools at a glance
Ranked by compiler-gate discipline and `any`-density track record.
| Tool | Type | Compiler-gated | `any` discipline | Price | Best for |
|---|---|---|---|---|---|
| Refactyl | Verified migration tool | Never-`any` policy, benchmarked on 5 OSS repos | $0–$299/mo or project quote | Teams shipping a verified migration to production | |
| ts-migrate | OSS codemod (Airbnb) | Leans on `any` to get to a green build | Free | Free deterministic first pass; plan to clean up `any`s | |
| jscodeshift | OSS AST toolkit | You control it entirely | Free | Custom transforms you write yourself | |
| Cursor | AI code editor | Depends on how you prompt it | $20–$120/user/mo | In-editor exploration; small, low-stakes migrations | |
| Claude Code | AI agent (terminal) | Depends on prompting; excellent reasoning | Claude Pro/Max + API usage | Gnarly one-off refactors; you verify the output yourself | |
| Devin | Autonomous agent | Case-by-case; no published any-density data | Enterprise pricing | Large orgs with budget for fine-tuning and oversight | |
| Codemod | Enterprise platform | Campaign-dependent; compiler-aware code graphs | $1,000+/mo | Enterprise modernization programs across thousands of repos | |
| DIY (paste into an LLM) | Manual | Poor without active policing: 3–30× more `any` vs Refactyl | "Free" + your weekend | Single-file tweaks you review personally |
compiler-gated · partial · not gated · `any`-density data from refactyl.com/benchmark (5 OSS repos, reproducible)
The honest read on each tool
Refactyl
Verified migration tool
Gates every file through the real compiler, runs a Verify & Repair loop until the build is clean, enforces a never-`any` policy, and ships a flagged file rather than guessing on anything it can't safely convert. Has a public benchmark you can reproduce.
Catch: Four migration paths today (JS→TS, Vue 2→3, Next Pages→App Router, Express→Fastify). Not a general-purpose coding tool.
ts-migrate
OSS codemod
Deterministic, battle-tested, and free. Created by Airbnb for large JS→TS migrations. Fast to run on an existing codebase as a scaffold.
Catch: Failed to run on modern Node on every repo in our benchmark. When it does run, it inserts `any` aggressively to get to a green build. Treat it as step one, not the finish line.
jscodeshift / hypermod
OSS AST toolkit
Precise, deterministic, and free. The right tool if you're writing reusable transform recipes, like renaming an API across a monorepo. You control exactly what changes.
Catch: You write the transforms. That's a programming project, not a migration tool. Good for targeted codemods; not suited to a whole-codebase JS→TS.
Cursor
AI code editor
Already installed, already paid for, and genuinely excellent at driving a migration agent-mode for a focused session. The IDE experience is hard to beat.
Catch: No compiler gate. You find out what didn't build yourself, in code review. Will reach for `any` to silence errors without you noticing. Fine for small migrations; production-scale migrations need a gate.
Claude Code
AI agent
Reasoning that holds up on gnarly refactors, and it tracks cross-file relationships well. Terminal-native, fast, included in Claude Pro/Max.
Catch: No compiler gate, so you re-prompt until it's clean, with no guarantee it didn't cheat with `any`. Context-window limits bite on large repos. You are the Verify & Repair loop.
Devin
Autonomous agent
Has proof points for very large migrations (Nubank case study: ~6M LOC, 18mo→2mo). Runs build loops autonomously.
Catch: Enterprise pricing and fine-tuning overhead. No published `any`-density data or head-to-head benchmark. The Nubank case was a data-class migration, not JS→TS specifically.
Codemod
Enterprise platform
Compiler-aware code graph, campaign orchestration across thousands of repos, SOC2/BYOC today, dedicated field engineers. Serious platform for serious programs.
Catch: Starts at $1,000/month. Purpose-built for enterprises running modernization at scale, overkill for one team with one migration.
DIY (paste into ChatGPT / Claude)
Manual
Zero new tools, total control, runs on the subscription you already pay. Works well for one or two files you review personally.
Catch: No compiler gate, context-window limits on real repos, 3–30× more `any` than Refactyl on the public benchmark. The hidden cost is the hours you spend playing compiler.
How to actually choose
One file, or a tiny package you'll review every line of
Paste it into Claude or run ts-migrate. Free, fast, you know the output.
You want it free, deterministic, and don't mind cleaning up `any`s
ts-migrate. Treat it as step one; audit the `any`s before you ship.
You live in Cursor and the migration is small
Do it there, but personally verify every file compiles with no new `any`s before you merge.
Shipping a real migration to production: a real repo, real deadline
Refactyl. Compiler-gated, benchmarked, every file verified or clearly flagged. You review a clean diff instead of debugging a hopeful one.
Modernizing thousands of repos with a compliance team
Codemod or Moderne. Campaign orchestration across repos, SOC2, dedicated FDEs.
Live migration paths
Each path has its own compiler gate, deterministic rules, and detailed docs.
Try it now
Paste Express. Get Fastify. Right here.
The same engine that migrates whole repos, scoped to a single file. Free, in your browser, no signup.
// public demo model · never paste secrets, API keys, or .env values
// fastify output appears here
// run transform to see the conversion
// free preview · 2 transforms per hour
FAQ
JS→TS migration tools: common questions
Honest answers from the people who benchmarked them.
Ready to see for yourself?
Run the free benchmark repo, or try your own.
We think verification is the whole game. That's why we built Refactyl and published the benchmark so you don't have to take our word for it. One free migration per month, up to 100 files. No credit card.
No credit card · Docker-sandboxed · Deleted on handoff · Never used for training