backprop
Bug → spec protocol. When a bug is found or a test fails, trace the cause, decide whether a new §V invariant would catch recurrence, append to §B. This is the one non-obvious thing SDD does that plan-then-execute doesn't. Triggers on test failure, bug report, post-mortem, or explicit user ask.
npx skills add JuliusBrussee/cavekit --skill backprop --agent claude-code
Same command for any agent — swap --agent for codex, cursor, copilot.
Weekly change comes from our own snapshots, not the repository page — it measures attention, not adoption.
# backprop — bug → spec Plan-then-execute fixes the code & forgets. SDD fixes the code AND edits spec so recurrence is impossible. That edit is backprop. ## WHEN TO BACKPROP - Test failed at `/build` verification. - User reports bug. - Post-mortem after production incident. - `/check` flags VIOLATE with root cause found. ## SIX STEPS ### 1. TRACE Read failure output / bug report. Find exact file:line of wrong behavior. Name root cause in one caveman sentence. ### 2. ANALYZE Ask three questions: - Would a new §V invariant catch this class of bug? (most common: yes) - Is §I wrong — did spec claim shape the code cannot deliver? (sometimes) - Is §T wrong — did we build the wrong thing? (rare but real) ### 3. PROPOSE Draft the spec change. Never skip §B; §V/§I/§T are case-by-case. Template: ``` §B row: B<next>|<date>|<root cause>|V<N> §V line: V<next>: <testable rule that would have caught it> ``` Example: ``` §B row: B3|2026-04-20|refund job ran twice on retry|V7 §V line: V7: ∀ refund → idempotency key check before charge reversal ``` ### 4. GENERATE TEST New invariant without test = lie. Add failing test first. Name test so it cites the invariant: `TestV7_RefundIdempotent`. ### 5. VER
- WHEN TO BACKPROP
- SIX STEPS
- 1. TRACE
- 2. ANALYZE
- 3. PROPOSE
- 4. GENERATE TEST
- 5. VERIFY
- 6. LOG
- WHAT MAKES A GOOD INVARIANT
- WHEN NOT TO ADD §V
- OUTPUT SHAPE
What does the backprop skill do?
Bug → spec protocol. When a bug is found or a test fails, trace the cause, decide whether a new §V invariant would catch recurrence, append to §B. This is the one non-obvious thing SDD does that plan-then-execute doesn't. Triggers on test failure, bug report, post-mortem, or explicit user ask.
How do I install it?
Run `npx skills add JuliusBrussee/cavekit --skill backprop --agent claude-code` — it drops the skill into your project so the agent can pick it up. Swap the --agent value for codex, cursor or copilot if you use one of those.
Where does this skill come from?
From JuliusBrussee/cavekit, a repository with 1,133 stars. We read it straight from the repository tree rather than a submitted listing, so what you see here is what is actually published.
Is a popular skill a good skill?
Not necessarily. Stars measure attention, not adoption — a repository can trend for a week and be abandoned. That is why we show the weekly change from our own snapshots next to the total, instead of a single flattering number.