legacy-change
Skill1 starsChanged 41 days agoMITView on GitHub
Change legacy code safely with characterization coverage. Use when editing poorly tested old modules, unknown systems, or brittle production paths.
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The file
We split this skill into the rules it gives an agent
5 rules. About 0 are common, 5 are distinctive, and 0 are very specific to this project.
≈0
Common · estimate
Many files like this have a rule of this kind.
≈5
Distinctive · estimate
This author's own choices. Worth a look.
0
Very specific
Tied to their project's names, files or tools. Probably skip.
- Common
- Distinctive
- Very specific
- Distinctive: line 12
Prefer adapter/facade over rewriting the core.
- Distinctive: line 14
Only then refactor within the covered seam.
- Distinctive: line 18
Do not big-bang rewrite legacy modules for a small fix.
- Distinctive: line 20
Avoid drive-by cleanups outside the seam.
- Distinctive: line 21
If no test harness exists, add the thinnest possible one at the boundary.
≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.
Files
Legacy Change
Process
- Find the smallest seam around the change.
- Characterize current behavior with tests or golden fixtures before editing.
- Prefer adapter/facade over rewriting the core.
- Make the behavior change in a thin step; keep characterization green.
- Only then refactor within the covered seam.
Rules
- Do not big-bang rewrite legacy modules for a small fix.
- Record discovered invariants in tests, not only in chat.
- Avoid drive-by cleanups outside the seam.
- If no test harness exists, add the thinnest possible one at the boundary.
Exit
- Before-behavior captured
- Intended change verified
- Rollback path understood
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