TDD Workflow
hellangleZ/burn-in-cceverywhere-ralph
A skill your agent uses when writing new features, fixing bugs, or refactoring code.
Software-engineering heuristics based on Mark Seemann's Code That Fits in Your Head (2021), updated for agent-driven development.
Install Code That Fits In Your Head
$ npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install CodeAlive-AI/ai-driven-development code-that-fits-in-your-head --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/CodeAlive-AI/ai-driven-development.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/code-that-fits-in-your-head .claude/skills/code-that-fits-in-your-head && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "code-that-fits-in-your-head" agent skill from https://github.com/CodeAlive-AI/ai-driven-development/tree/main/skills/code-that-fits-in-your-head into .claude/skills/code-that-fits-in-your-head/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "code-that-fits-in-your-head", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/CodeAlive-AI/ai-driven-development/tree/main/skills/code-that-fits-in-your-headType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install CodeAlive-AI/ai-driven-development code-that-fits-in-your-head --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/CodeAlive-AI/ai-driven-development.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/code-that-fits-in-your-head .agents/skills/code-that-fits-in-your-head && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "code-that-fits-in-your-head" agent skill from https://github.com/CodeAlive-AI/ai-driven-development/tree/main/skills/code-that-fits-in-your-head into .agents/skills/code-that-fits-in-your-head/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "code-that-fits-in-your-head", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install CodeAlive-AI/ai-driven-development code-that-fits-in-your-head --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/CodeAlive-AI/ai-driven-development.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/code-that-fits-in-your-head .cursor/skills/code-that-fits-in-your-head && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "code-that-fits-in-your-head" agent skill from https://github.com/CodeAlive-AI/ai-driven-development/tree/main/skills/code-that-fits-in-your-head into .cursor/skills/code-that-fits-in-your-head/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "code-that-fits-in-your-head", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/CodeAlive-AI/ai-driven-development.git --path skills/code-that-fits-in-your-head--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install CodeAlive-AI/ai-driven-development code-that-fits-in-your-head --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/CodeAlive-AI/ai-driven-development.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/code-that-fits-in-your-head .gemini/skills/code-that-fits-in-your-head && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "code-that-fits-in-your-head" agent skill from https://github.com/CodeAlive-AI/ai-driven-development/tree/main/skills/code-that-fits-in-your-head into .gemini/skills/code-that-fits-in-your-head/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "code-that-fits-in-your-head", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install CodeAlive-AI/ai-driven-development code-that-fits-in-your-headInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/CodeAlive-AI/ai-driven-development.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/code-that-fits-in-your-head .github/skills/code-that-fits-in-your-head && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "code-that-fits-in-your-head" agent skill from https://github.com/CodeAlive-AI/ai-driven-development/tree/main/skills/code-that-fits-in-your-head into .github/skills/code-that-fits-in-your-head/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "code-that-fits-in-your-head", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install CodeAlive-AI/ai-driven-development code-that-fits-in-your-head --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/CodeAlive-AI/ai-driven-development.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/code-that-fits-in-your-head .opencode/skills/code-that-fits-in-your-head && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "code-that-fits-in-your-head" agent skill from https://github.com/CodeAlive-AI/ai-driven-development/tree/main/skills/code-that-fits-in-your-head into .opencode/skills/code-that-fits-in-your-head/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "code-that-fits-in-your-head", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
code-that-fits-in-your-head- GitHub stars
- 158
- Token cost
- ~1.7k tokens
- SKILL.md length
- 689 words
- Files
- 65 (incl. references)
- Skills in repo
- 22
- Repo updated
- First seen
- Licence
- MIT
At a glance
Software-engineering heuristics based on Mark Seemann's Code That Fits in Your Head (2021), updated for agent-driven development.
- Works in 5 steps: Successful software endures. Prefer… → Complexity is the enemy, not task size.… → Heuristics, not laws. Understand the… → …
- Refactoring accidental complexity
- SKILL.md covers Philosophy (Why This Skill…, How to Use This Skill, Chapter Index and Workflows
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
What it does
Code That Fits In Your Head is an agent skill from CodeAlive-AI/ai-driven-development. Software-engineering heuristics based on Mark Seemann's Code That Fits in Your Head (2021), updated for agent-driven development. Use when writing or reviewing code, refactoring accidental complexity or a Big Ball of Mud, controlling technical or architectural debt in generated code, designing APIs and invariants, adding a feature through a walking skeleton and acceptance tests, debugging a defect with reproducible tests or bisection, threat-modelling endpoints and trust boundaries with STRIDE, planning a legacy…
Its SKILL.md is about 1.7k tokens, which your agent loads only when the skill is triggered. The skill folder holds 69 other files, including reference files (for example `README.md`, `guidelines.md` and `references/agent-native/hallucination-debugging.md`).
It sits in Testing & QA, covering End-to-end testing, Threat modeling and Refactoring. It works with Git. The repository describes itself as: Practices, protocols, and skills for AI-driven software development. Skills and safety hooks for Claude Code, Codex, OpenCode, Cursor, Antigravity, and any agent supporting the… The licence is MIT.
When your agent uses it
- Refactoring accidental complexity
- A Big Ball of Mud
- Controlling technical
- Architectural debt in generated code
Example prompts
- “/code-that-fits-in-your-head”
Workflow steps
5 steps, taken from the first numbered list in SKILL.md.
- Successful software endures. Prefer changes that preserve clear boundaries and keep future change affordable.
- Complexity is the enemy, not task size. Agents can complete changes spanning tens of thousands of lines when architecture, plan, and…
- Heuristics, not laws. Understand the purpose of a rule before applying or relaxing it. Project policy overrides generic formatting and…
- Verification is part of design. Types, tests, schemas, architecture checks, observability, and explicit acceptance criteria constrain both…
- Code is a liability. Generated volume is not progress. Prefer the smallest coherent design that solves the problem without accumulating…
What it can do on your machine
Read from SKILL.md and the folder at commit 4cfeb10. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Code That Fits In Your Head loads about 1.7k tokens when it runs, and up to ~65k if it reads all its reference files. Until then it costs about 224 tokens; SKILL.md has 689 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from CodeAlive-AI/ai-driven-development at commit 4cfeb10, republished under its MIT licence (© CodeAlive-AI). 689 words, ~1,725 tokens.
Download SKILL.mdSave it as
.claude/skills/code-that-fits-in-your-head/SKILL.md (or your agent's skills folder). This skill also uses 64 other files; get the full folder from GitHub.- name
- code-that-fits-in-your-head
- description
- Software-engineering heuristics based on Mark Seemann's Code That Fits in Your Head (2021), updated for agent-driven development. Use when writing or reviewing code, refactoring accidental complexity or a Big Ball of Mud, controlling technical or architectural debt in generated code, designing APIs and invariants, adding a feature through a walking skeleton and acceptance tests, debugging a defect with reproducible tests or bisection, threat-modelling endpoints and trust boundaries with STRIDE, planning a legacy or Strangler migration with rollback, or setting up a maintainable codebase. Covers decomposition and cyclomatic complexity, cohesion, encapsulation, outside-in TDD, separation of concerns, Git/review discipline, safe evolution, and troubleshooting. Not for language syntax, framework tutorials, production incident response, or performance profiling.
Code That Fits in Your Head
Engineering heuristics for sustainable software, based on Mark Seemann's 2021 book and clearly labelled agent-era amendments.
Code examples are C#-first; every rule and the tooling tables are language-neutral.
Philosophy (Why This Skill Exists)
Software development is principally a design activity, not construction. An agent may produce most of the text, but people still review, operate, extend, and own the resulting system. These heuristics make software sustainable: understandable, resistant to architectural erosion, and cheap to change after thousands of decisions.
Core mental model from Chapter 1:
| Metaphor | What it gets right | What it misses |
|---|---|---|
| Building a house | Plans, structure | Software endures; there's no construction phase (compiling is free); dependencies can start anywhere |
| Growing a garden | Pruning, refactoring, tending | Code does not improve by itself; generated code still needs stewardship |
| Art / craft | Skill, mastery, situational knowledge | Doesn't scale; leaves newcomers without guidance |
| Engineering (the target) | Heuristics, review, sign-off, checklists | We're not there yet — physical-construction calculations don't apply |
"The act of describing a program in unambiguous detail and the act of programming are one and the same." — Kevlin Henney
Practical implications for a code agent:
- Successful software endures. Prefer changes that preserve clear boundaries and keep future change affordable.
- Complexity is the enemy, not task size. Agents can complete changes spanning tens of thousands of lines when architecture, plan, and acceptance criteria are sound. Reject needless coupling, duplication, hidden effects, and unverifiable bulk—not large scope by itself.
- Heuristics, not laws. Understand the purpose of a rule before applying or relaxing it. Project policy overrides generic formatting and workflow conventions.
- Verification is part of design. Types, tests, schemas, architecture checks, observability, and explicit acceptance criteria constrain both human- and agent-written code.
- Code is a liability. Generated volume is not progress. Prefer the smallest coherent design that solves the problem without accumulating debt.
See references/foundations/ for more on sustainability, readability, and brain-limited design.
How to Use This Skill
- Identify the user's task (writing, reviewing, debugging, security review, setting up, etc.)
- Read
guidelines.md— it maps tasks and symptoms to specific reference files - Load only the reference files relevant to the current task (progressive disclosure)
- Apply the rules; when in doubt, consult
references/practices-glossary/for cross-references - When a rule proves repeatedly useful in a repository, operationalize it (
workflows/operationalize-finding.md) so it persists as a gate and in project agent instructions.
Show full SKILL.md (292 more words)Show less
Chapter Index
| Topic | Use when... |
|---|---|
references/foundations/ | Sustainability, readability, complexity control, and code as liability |
references/codebase-setup/ | Starting or inheriting a code base — git, build automation, warnings-as-errors |
references/outside-in-tdd/ | Writing new features test-first; walking skeleton, AAA, triangulation, devil's advocate, editing tests |
references/encapsulation/ | Designing types with invariants; DTO vs Domain Model, always-valid, Postel's law, parse-don't-validate |
references/decomposition/ | Controlling method and system complexity; cyclomatic complexity, cohesion, coupling, feature envy, fractal architecture |
references/api-design/ | Designing a public API; affordance, poka-yoke, CQS, hierarchy of communication, naming over comments |
references/separation-of-concerns/ | Adding cross-cutting concerns; Decorator pattern, logging, what to log, performance vs legibility |
references/teamwork-git/ | Writing commits, reviewing changes, continuous integration, collective ownership |
references/evolution/ | Changing running systems; feature flags, Strangler pattern, versioning, regular dependency updates, Conway's law |
references/troubleshooting/ | Debugging a defect; scientific method, rubber ducking, reproduce-as-test, bisection, non-deterministic defects |
references/security/ | Threat modelling; STRIDE (spoofing, tampering, repudiation, info disclosure, DoS, elevation) |
references/code-navigation/ | Onboarding to a code base; big picture, file organisation, cycles, property-based testing, behavioural code analysis |
references/tooling/ | Executable measurement commands: complexity, cycles, duplication, dead code, hotspots, mutation testing |
references/practices-glossary/ | Looking up a named book practice and its current status |
⚠️ Editorial amendments (NOT from the book)
The folder below is NOT content from Seemann's book. It contains our own additions covering agent-specific concerns the 2021 book does not address. Do not attribute these files to Seemann. See references/agent-native/knowledge.md.
| Topic | Use when... |
|---|---|
references/agent-native/ | Agent-specific verification integrity, hallucination and dependency grounding, executable guardrails, and accountable review |
Workflows
Composite step-by-step processes live in workflows/:
| Task | Workflow |
|---|---|
| Review a pull request / piece of code | workflows/review-code.md |
| Add a new feature from scratch | workflows/add-feature-outside-in.md |
| Investigate and fix a defect | workflows/debug-defect.md |
| Threat-model a new endpoint | workflows/threat-model.md |
| Turn a recurring finding into an executable gate and persist it in project memory | workflows/operationalize-finding.md |
See guidelines.md for the full routing layer (task → file, symptom → file).
© CodeAlive-AI, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 64 other files (references) in skills/code-that-fits-in-your-head of CodeAlive-AI/ai-driven-development.
- SKILL.md
- README.md
- guidelines.md
- references/agent-native/hallucination-debugging.md
- references/agent-native/knowledge.md
- references/agent-native/reviewability.md
- references/agent-native/types-as-guardrails.md
- references/agent-native/verification-loops.md
- references/api-design/examples.md
- references/api-design/knowledge.md
- references/api-design/rules.md
- references/code-navigation/knowledge.md
- references/code-navigation/rules.md
- references/codebase-setup/checklist.md
- references/codebase-setup/knowledge.md
- references/codebase-setup/rules.md
- … and 49 more
Open the folder on GitHubat commit 4cfeb10
Compare with similar skills
Code That Fits In Your Head next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Code That Fits In Your Head this skillCodeAlive-AI/ai-driven-development | 158 | — | ~1.7k | Automated safety check: Pass | MIT | |
| TDD WorkflowhellangleZ/burn-in-cceverywhere-ralph | 112 | 11 repos | ~2.4k | Automated safety check: Pass | None | |
| TDD Workflowaffaan-m/ECC | 276k | 1 repos | ~2.6k | Automated safety check: Pass | MIT | |
| Absolute Workmaddhruv/absolute | 218 | — | ~5.3k | Automated safety check: Pass | MIT | |
| Refactortestdouble/han | 279 | — | ~3.1k | Automated safety check: Pass | MIT | |
| Test Guidelinesgetsentry/sentry-dart | 873 | — | ~3.1k | Automated safety check: Pass | MIT |
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Categories
Questions about Code That Fits In Your Head
What does Code That Fits In Your Head do?
Software-engineering heuristics based on Mark Seemann's Code That Fits in Your Head (2021), updated for agent-driven development. Code That Fits In Your Head is an agent skill from CodeAlive-AI/ai-driven-development. Software-engineering heuristics based on Mark Seemann's Code That Fits in Your Head (2021), updated for agent-driven development.
When should I use Code That Fits In Your Head?
Code That Fits In Your Head fits situations like: refactoring accidental complexity; A Big Ball of Mud; controlling technical; architectural debt in generated code.
How do I install Code That Fits In Your Head in Claude Code?
Run `npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a claude-code`. Or copy the skill folder (skills/code-that-fits-in-your-head in CodeAlive-AI/ai-driven-development) into .claude/skills/code-that-fits-in-your-head in your project. Claude Code loads it when a task matches its description.
How do I install Code That Fits In Your Head in Codex?
Run `npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a codex`. Or copy the skill folder (skills/code-that-fits-in-your-head in CodeAlive-AI/ai-driven-development) into .agents/skills/code-that-fits-in-your-head in your project. Codex loads it when a task matches its description.
Can I use Code That Fits In Your Head in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-head -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/code-that-fits-in-your-head, .gemini/skills/code-that-fits-in-your-head, .github/skills/code-that-fits-in-your-head and .opencode/skills/code-that-fits-in-your-head in your project.
What does Code That Fits In Your Head need to run?
SKILL.md names no scripts, command-line tools or credentials: Code That Fits In Your Head is instructions for the agent only.
Does Code That Fits In Your Head access the network?
SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.
Is Code That Fits In Your Head safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Code That Fits In Your Head use?
Code That Fits In Your Head is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Code That Fits In Your Head use?
About 1.7k tokens (SKILL.md is roughly 6.9k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 63k tokens, read only when the agent opens those files.
What are the alternatives to Code That Fits In Your Head?
Skills that share tags, products or a category with Code That Fits In Your Head: TDD Workflow (hellangleZ/burn-in-cceverywhere-ralph, 112 stars), TDD Workflow (affaan-m/ECC, 276k stars), Absolute Work (maddhruv/absolute, 218 stars) and Refactor (testdouble/han, 279 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Code That Fits In Your Head?
CodeAlive-AI (a GitHub organization) maintains it in CodeAlive-AI/ai-driven-development, which has 158 GitHub stars. The repository holds 22 skills in this directory. The repository was last updated on October 8, 2026.
Source: CodeAlive-AI/ai-driven-development on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.