How do I install the Code Migration skill?

Run npx skillmds@latest add anthropics/code-migration in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Code Migration safe to use?

This skill has not completed SkillMD's automated safety review yet. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Code Migration?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Code Migration free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Code Migration?

anthropics (@anthropics) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Code Migration by anthropics — Agent Skill

Name: Code Migration
Author: anthropics

Code Migration

Run a large-scale language migration with the six-step process: create the map and the rules, stress-test the rules, translate everything, compile, run it, match behavior. Use when the user wants to migrate, port, or rewrite a codebase from one language to another ("migrate this to Rust", "port our Python CLI to TypeScript", "should we rewrite this in Go?"), or asks for a migration feasibility assessment. Not for incremental JS→TS adoption — that needs no machinery — or single-file conversions.

anthropics f4f2518 3.9 KB Updated Sep 17, 2026

File contents

Code migration (six-step process)

You are orchestrating a language migration using the Claude Code Migration Kit. [kit path]/README.md defines the process; [kit path]/CLAUDE.md defines your standing rules — read both before acting (set [kit path] when installing this skill). The standing rules override convenience: queues live on disk, sign-off gates end workflows, the rulebook is read-only inside loops, reviewers are adversarial and separate.

Routing

No migration artifacts exist yet (migration/ absent): run prompts/00-feasibility.md. Produce the report, deliver the verdict, STOP. Do not begin Step 1 in the same session, even if the verdict is "migrate now" — the human kicks off each phase. 1b. Feasibility signed off, no judge yet: before Step 1, confirm a judge exists that runs against both old and new code through the public surface. If the existing suite is public-surface (or already in a third language), it's the judge — carry it to Step 6. If it imports internals, run prompts/00b-judge-setup.md to build and validate a portable parity harness (validated against the original AND deliberately broken code) and STOP at its gate. Never start Step 1 without a judge — there's no exit condition without one.
Feasibility and judge signed off, no map/rules: run Step 1 — adapt a scripts/depmap_* for the source ecosystem (prompts/01), copy templates/RULEBOOK.md to migration/RULEBOOK.md and draft it with the human (the policy decisions are theirs; survey the codebase for the facts), then prompts/02 for the gap inventory. Each ends at its own gate.
Step 1 signed off: confirm the HUMAN has installed .claude/settings.json from templates/settings.json — prompt 03 verifies it; never install it yourself — then run prompts/03-stress-test.md. But FIRST check the rulebook's §0 posture: if this is a redesign migration, the bakeoff is invalid; substitute adversarial design-doc review and tell the human why.
Stress test signed off: confirm migration/manifest.tsv exists (prompt 01's closing action generates it), then run prompts/04-translation-kickoff.md with scripts/queue_runner.mjs as the queue — first check the referee price: if the target's typecheck is cheap, the dissolve edit is the human's act at the gate — ask them to remove those denies from settings.json; never edit it yourself (README Step 4 dissolves into Step 3).
Translation queue empty: Step 4 via prompts/05-survey-build.md (survey build → machine queue → fixers without compiler access; skip it entirely if Step 4 dissolved into Step 3), then Step 5 (hello world, smoke), then Step 6 (inherited suite burndown, or parity referee against the old code).
Step 6 done-gate passed (both counts documented — README Step 6): run prompts/06-post-parity.md — collect the port markers, classify fix-now vs document-and-close, ship each fix as its own flagged change proved by a parity re-run. Ends at its own gate.

Constant behaviors

Report progress as burndown numbers (queue_runner.mjs status), not prose.
A failure seen three times is a rule bug: stop fixing instances, queue the amendment, propose regenerating the slice.
"Don't migrate" and "stop here" are valid recommendations at every gate.

---name: code-migrationdescription: Run a large-scale language migration with the six-step process: create the map and the rules, stress-test the rules, translate everything, compile, run it, match behavior. Use when the user wants to migrate, port, or rewrite a codebase from one language to another ("migrate this to Rust", "port our Python CLI to TypeScript", "should we rewrite this in Go?"), or asks for a migration feasibility assessment. Not for incremental JS→TS adoption — that needs no machinery — or single-file conversions.---# Code migration (six-step process)You are orchestrating a language migration using the Claude Code MigrationKit. [kit path]/README.md defines the process; [kit path]/CLAUDE.md definesyour standing rules — read both before acting (set [kit path] when installingthis skill). The standing rules overrideconvenience: queues live on disk, sign-off gates end workflows, the rulebookis read-only inside loops, reviewers are adversarial and separate.## Routing1. **No migration artifacts exist yet** (`migration/` absent): run `prompts/00-feasibility.md`. Produce the report, deliver the verdict, STOP. Do not begin Step 1 in the same session, even if the verdict is "migrate now" — the human kicks off each phase.1b. **Feasibility signed off, no judge yet:** before Step 1, confirm a judge exists that runs against both old and new code through the public surface. If the existing suite is public-surface (or already in a third language), it's the judge — carry it to Step 6. If it imports internals, run `prompts/00b-judge-setup.md` to build and validate a portable parity harness (validated against the original AND deliberately broken code) and STOP at its gate. Never start Step 1 without a judge — there's no exit condition without one.2. **Feasibility and judge signed off, no map/rules:** run Step 1 — adapt a `scripts/depmap_*` for the source ecosystem (`prompts/01`), copy `templates/RULEBOOK.md` to `migration/RULEBOOK.md` and draft it with the human (the policy decisions are theirs; survey the codebase for the facts), then `prompts/02` for the gap inventory. Each ends at its own gate.3. **Step 1 signed off:** confirm the HUMAN has installed `.claude/settings.json` from `templates/settings.json` — prompt 03 verifies it; never install it yourself — then run `prompts/03-stress-test.md`. But FIRST check the rulebook's §0 posture: if this is a redesign migration, the bakeoff is invalid; substitute adversarial design-doc review and tell the human why.4. **Stress test signed off:** confirm `migration/manifest.tsv` exists (prompt 01's closing action generates it), then run `prompts/04-translation-kickoff.md` with `scripts/queue_runner.mjs` as the queue — first check the referee price: if the target's typecheck is cheap, the dissolve edit is the human's act at the gate — ask them to remove those denies from settings.json; never edit it yourself (README Step 4 dissolves into Step 3).5. **Translation queue empty:** Step 4 via `prompts/05-survey-build.md` (survey build → machine queue → fixers without compiler access; skip it entirely if Step 4 dissolved into Step 3), then Step 5 (hello world, smoke), then Step 6 (inherited suite burndown, or parity referee against the old code).6. **Step 6 done-gate passed** (both counts documented — README Step 6): run `prompts/06-post-parity.md` — collect the port markers, classify fix-now vs document-and-close, ship each fix as its own flagged change proved by a parity re-run. Ends at its own gate.## Constant behaviors- Report progress as burndown numbers (`queue_runner.mjs status`), not prose.- A failure seen three times is a rule bug: stop fixing instances, queue the amendment, propose regenerating the slice.- "Don't migrate" and "stop here" are valid recommendations at every gate.

Frequently asked questions