Backprop

by JuliusBrussee

Backprop is a Quality skill for Claude Code, published by JuliusBrussee in cavekit.

1.1K stars86 forkson JuliusBrussee/cavekitAdded 2026/08/20Repository updated 2026/08/14

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claude-codeparallel-agentsskillsspec-driven-developmenttest-driven-development

Install in seconds

Install Backprop

Copy Backprop into your Claude Code skills folder. Run the command in your terminal, or review the source on GitHub before installing.

terminal

npx degit https://github.com/JuliusBrussee/cavekit/tree/main/skills/backprop ~/.claude/skills/backprop

Requires Node.js. Downloads this skill only — not the rest of the repository — into your Claude Code skills folder.

Without Node.js

git clone https://github.com/JuliusBrussee/cavekit.git

Clones the whole repository, then copy the skill’s own directory into your skills folder yourself.

In this catalog

Source file: skills/backprop/SKILL.md in JuliusBrussee/cavekit
Installs to: ~/.claude/skills/backprop
Collection: One of 9 skills cataloged from this repository
Category: Quality — 1354 skills

What Backprop does

Backprop traces a bug or failing test to its root cause, then appends a §B entry and usually a §V invariant to SPEC.md so recurrence is impossible. Use it after test failures, bug reports, post-mortems, or VIOLATE flags.

Backprop is cataloged under Quality on DirSkills. Backprop comes from a repository tagged claude-code, parallel-agents, skills, spec-driven-development and test-driven-development.

Documentation

README

Excerpt

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.

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.

This is the opening of the README. Read the full README on GitHub.

Commands Backprop provides

Slash commands named in this skill’s SKILL.md, listed in the order they first appear.

/build
/check

Frequently asked about Backprop

What else does JuliusBrussee publish alongside Backprop?
Backprop is one of 9 skills that DirSkills catalogs from JuliusBrussee/cavekit, the repository it ships in. Its siblings there include Adversarial Spec Review, Build and Caveman. Each one is a separate skill with its own page in this directory, installs the same way Backprop does, and is maintained by JuliusBrussee in that same repository. The rest of the collection is listed on the JuliusBrussee/cavekit page.
How does Backprop compare to other Quality skills?
Backprop ranks #767 by stars among the 1354 Quality skills in this catalog. The most-starred ones next to it are Benchmark, Benchmark Optimization Loop and API Design Patterns. DirSkills ranks by the star count of the repository each skill ships in, so that order reflects how popular those repositories are rather than any review of Backprop against them. Open each page to compare what they document and how they install.