
Skill
code-migration
perform large-scale language code migrations
Description
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.
SKILL.md
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): runprompts/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, runprompts/00b-judge-setup.mdto 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), copytemplates/RULEBOOK.mdtomigration/RULEBOOK.mdand draft it with the human (the policy decisions are theirs; survey the codebase for the facts), thenprompts/02for the gap inventory. Each ends at its own gate. - Step 1 signed off: confirm the HUMAN has installed
.claude/settings.jsonfromtemplates/settings.json— prompt 03 verifies it; never install it yourself — then runprompts/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.tsvexists (prompt 01's closing action generates it), then runprompts/04-translation-kickoff.mdwithscripts/queue_runner.mjsas 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.
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