Is the Code That Fits In Your Head skill free?

Yes. The skill itself is free from CodeAlive-AI/ai-driven-development. SkillProof publishes the install command and an independent test verdict at no cost.

What is the Code That Fits In Your Head SkillProof Score?

9.6/10 — installs cleanly 5/5, triggers reliably 5/5, output vs. baseline 9/10, docs & honesty 5/5.

How do I install Code That Fits In Your Head?

Copy the install command from this page, run it in your terminal, and restart Claude Code. Skills live in ~/.claude/skills/ (global) or .claude/skills/ inside a project.

Can I use Code That Fits In Your Head with Cursor, Copilot, Gemini CLI, Codex or other AI tools?

The SKILL.md format is native to Claude (Claude Code, Desktop, claude.ai). The instructions inside adapt to other assistants: Cursor rules, GitHub Copilot instructions, Windsurf rules, Custom GPTs, AGENTS.md for OpenAI Codex, and GEMINI.md for Google Gemini CLI — our conversion guides cover each, and the free converter on the tools page does the wrapping for you.

Code That Fits In Your Head

Seemann's engineering heuristics (complexity limits, TDD, API design, STRIDE) routed to the exact file a task needs.

by CodeAlive-AI · CodeAlive-AI/ai-driven-development

Tested · Works

Install — copy the command Download source ↗

Test report

Verdict: Tested · Works
Score: 9.6/10
Tested: Jul 13, 2026
Environment: Claude Code 2.x (agent harness)
Upstream re-checked: Aug 10, 2026 · 88fe656

Fed it a 7-parameter, complexity-13 order-processing function and it flagged exact rule violations by number (cyclomatic complexity ceiling of 7, parse-don't-validate) instead of generic 'clean this up' review comments.

Scored on four weighted criteria — install, triggering, output vs. baseline, docs. How scoring works

Installs cleanly 5/5
Triggers reliably 5/5
Output vs. baseline 9/10
Docs & honesty 5/5

What Code That Fits In Your Head does

Encodes concrete, numbered heuristics from Mark Seemann's 'Code That Fits in Your Head' — cyclomatic complexity ceilings, the 80/24 method-size rule, parse-don't-validate, outside-in TDD, CQS, Strangler pattern, STRIDE threat modelling — behind a routing layer (guidelines.md) that maps each coding task to one or two specific reference files instead of loading everything. Triggers on code review, refactoring, API design, TDD, debugging, and security-review requests; explicitly excludes language syntax, framework tutorials, incident response, and performance profiling.

How to install Code That Fits In Your Head

git clone https://github.com/CodeAlive-AI/ai-driven-development
cd ai-driven-development
mkdir -p ~/.claude/skills
cp -r skills/code-that-fits-in-your-head ~/.claude/skills/code-that-fits-in-your-head

Skills live in ~/.claude/skills/ (global) or .claude/skills/ (per-project). Restart Claude Code after installing.

Commands — how to trigger Code That Fits In Your Head

/code-that-fits-in-your-head Seemann's engineering heuristics (complexity limits, TDD, API design, STRIDE) routed to the exact file a task needs.

It also activates on plain-language prompts like these:

Review this function against Seemann's complexity and size heuristics
Refactor this API using parse-don't-validate and CQS principles
Threat model this feature with STRIDE before I ship it

Frequently asked questions

Is the Code That Fits In Your Head skill free?: Yes. The skill itself is free from CodeAlive-AI/ai-driven-development. SkillProof publishes the install command and an independent test verdict at no cost.
Does Code That Fits In Your Head work with Claude Code?: We tested it with Claude Code 2.x (agent harness) on Jul 13, 2026. Verdict: Tested · Works. Fed it a 7-parameter, complexity-13 order-processing function and it flagged exact rule violations by number (cyclomatic complexity ceiling of 7, parse-don't-validate) instead of generic 'clean this up' review comments.
What is the Code That Fits In Your Head SkillProof Score?: 9.6/10 — installs cleanly 5/5, triggers reliably 5/5, output vs. baseline 9/10, docs & honesty 5/5.
How do I install Code That Fits In Your Head?: Copy the install command from this page, run it in your terminal, and restart Claude Code. Skills live in ~/.claude/skills/ (global) or .claude/skills/ inside a project.
Can I use Code That Fits In Your Head with Cursor, Copilot, Gemini CLI, Codex or other AI tools?: The SKILL.md format is native to Claude (Claude Code, Desktop, claude.ai). The instructions inside adapt to other assistants: Cursor rules, GitHub Copilot instructions, Windsurf rules, Custom GPTs, AGENTS.md for OpenAI Codex, and GEMINI.md for Google Gemini CLI — our conversion guides cover each, and the free converter on the tools page does the wrapping for you.