Spec Mutator

by JuliusBrussee

Spec Mutator is an AI Engineering skill for Claude Code, published by JuliusBrussee in cavekit.

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

View source on GitHub Download repo ZIP

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

Install in seconds

Install Spec Mutator

Copy Spec Mutator 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/spec ~/.claude/skills/spec

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/spec/SKILL.md in JuliusBrussee/cavekit
Installs to: ~/.claude/skills/spec
Collection: One of 9 skills cataloged from this repository
Category: AI Engineering — 2451 skills

What Spec Mutator does

Spec Mutator creates, amends, and backprops bugs into SPEC.md at the repo root, serving as the sole mutator of the project spec. Use it when writing a new spec, distilling from existing code, adding invariants, amending sections, or recording a bug via backprop.

Spec Mutator is cataloged under AI Engineering on DirSkills. Spec Mutator comes from a repository tagged claude-code, parallel-agents, skills, spec-driven-development and test-driven-development.

Documentation

README

Excerpt

spec — spec mutator

Read FORMAT.md at repo root if not already loaded. Caveman skill applies to all writes here.

DISPATCH

Inspect user request and project state:

No SPEC.md at repo root AND args describe idea → NEW
No SPEC.md AND from-code in args → DISTILL
SPEC.md exists AND args start bug: → BACKPROP
SPEC.md exists AND args start amend → AMEND
SPEC.md exists, no args → ask user which mode

INPUTS — spec is the sole mutator

The other verbs produce material; spec writes it. Ingest their handoff blocks into the right section, show a diff, write on OK:

grill → sharpened §G + §C
research → §R rows (add the §R section if absent)
review → drafted §V lines + the risk verdict
deepen → §I/§V/§T amendments

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

Commands Spec Mutator provides

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

/review
/build

Frequently asked about Spec Mutator

What else does JuliusBrussee publish alongside Spec Mutator?
Spec Mutator is one of 9 skills that DirSkills catalogs from JuliusBrussee/cavekit, the repository it ships in. Its siblings there include Adversarial Spec Review, Backprop and Build. Each one is a separate skill with its own page in this directory, installs the same way Spec Mutator does, and is maintained by JuliusBrussee in that same repository. The rest of the collection is listed on the JuliusBrussee/cavekit page.
How does Spec Mutator compare to other AI Engineering skills?
Spec Mutator ranks #1238 by stars among the 2451 AI Engineering skills in this catalog. The most-starred ones next to it are Architecture Decision Records, AI-First Engineering and Agentic OS. 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 Spec Mutator against them. Open each page to compare what they document and how they install.