Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add CodeAlive-AI/ai-driven-development --skill code-that-fits-in-your-headgit clone --depth 1 https://github.com/CodeAlive-AI/ai-driven-developmentWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/codealive-ai/ai-driven-development/code-that-fits-in-your-head)<a href="https://agentmods.dev/skills/codealive-ai/ai-driven-development/code-that-fits-in-your-head"><img src="https://agentmods.dev/badge/skills/codealive-ai/ai-driven-development/code-that-fits-in-your-head/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/codealive-ai/ai-driven-development/code-that-fits-in-your-head"><img src="https://agentmods.dev/badge/skills/codealive-ai/ai-driven-development/code-that-fits-in-your-head.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00169 | $0.01468 |
| Opus 5.5 | $0.00068 | $0.00587 |
| Sonnet 5.5 | $0.00034 | $0.00294 |
| Haiku 4.5 | $0.00017 | $0.00147 |
Grade A, and why
code-that-fits-in-your-head scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 85 lines — stays where its author put it; the contents beside it link to each section on GitHub.
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.
What ships with it
52 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
- guidelines.md 11 KB
- README.md 3.8 KB
- references/agent-native/hallucination-debugging.md 5.7 KB
- references/agent-native/knowledge.md 1.7 KB
- references/agent-native/reviewability.md 3.7 KB
- references/agent-native/types-as-guardrails.md 3.2 KB
- references/agent-native/verification-loops.md 3.9 KB
- references/api-design/examples.md 6.3 KB
- references/api-design/knowledge.md 2.6 KB
- references/api-design/rules.md 5.0 KB
- references/code-navigation/knowledge.md 4.4 KB
- references/code-navigation/rules.md 7.4 KB
- references/codebase-setup/checklist.md 5.4 KB
- references/codebase-setup/knowledge.md 2.2 KB
- references/codebase-setup/rules.md 6.3 KB
- references/decomposition/examples.md 7.8 KB
- references/decomposition/knowledge.md 4.4 KB
- references/decomposition/patterns.md 6.3 KB
- references/decomposition/rules.md 5.2 KB
- references/decomposition/smells.md 9.9 KB
- references/encapsulation/examples.md 7.2 KB
- references/encapsulation/knowledge.md 3.5 KB
- references/encapsulation/rules.md 6.8 KB
- references/evolution/examples.md 7.2 KB
- references/evolution/knowledge.md 2.6 KB
- references/evolution/patterns.md 9.7 KB
- references/evolution/rules.md 5.6 KB
- references/foundations/knowledge.md 4.6 KB
- references/foundations/rules.md 5.5 KB
- references/outside-in-tdd/examples.md 8.5 KB
- references/outside-in-tdd/knowledge.md 3.1 KB
- references/outside-in-tdd/patterns.md 5.9 KB
- references/outside-in-tdd/rules.md 6.9 KB
- references/practices-glossary/knowledge.md 12 KB
- references/security/checklist.md 4.5 KB
- references/security/knowledge.md 5.7 KB
- references/security/rules.md 9.0 KB
- references/separation-of-concerns/knowledge.md 2.2 KB
- references/separation-of-concerns/patterns.md 6.1 KB
- references/separation-of-concerns/rules.md 6.5 KB
- references/teamwork-git/checklist.md 3.8 KB
- references/teamwork-git/knowledge.md 3.6 KB
- references/teamwork-git/rules.md 5.0 KB
- references/tooling/commands.md 4.0 KB
- references/troubleshooting/knowledge.md 3.4 KB
- references/troubleshooting/patterns.md 7.2 KB
- references/troubleshooting/rules.md 5.3 KB
- workflows/add-feature-outside-in.md 9.5 KB
- workflows/debug-defect.md 6.8 KB
- workflows/operationalize-finding.md 4.2 KB
- workflows/review-code.md 6.9 KB
- workflows/threat-model.md 8.1 KB
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 85 lines · 169 tokens per session scan A 997c0361f3b8
code-that-fits-in-your-head is a skill published in the GitHub repository CodeAlive-AI/ai-driven-development (163 stars, last pushed 2d ago), licensed MIT. It adds 169 tokens to every session and 1,468 once invoked, about $0.0007 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
Other skills, from other repositories
code-review
Use when reviewing code for bugs, security issues, performance problems, or adherence to best practices. Provides structured code review with severity levels and actionable feedback.
application-security-pentesting
Production Application Security (AppSec) standards, OWASP Top 10 vulnerability remediation, SAST/DAST pipeline integration, secure code review, threat modeling, and defensive security posture.
arch-check
An architecture and implementation review tool that examines how a codebase is modeled, divided into responsibilities, organized into modules, and connected by dependencies. It also checks for issues such as circular dependencies, over-design, and violations of common design principles.
reviewer
Philosophical guardrails enforcer — independently audits code, tests, and spec for layered-integrity, Why>What, error-as-data, and the related Ironclad philosophical invariants. Activate only when the connected project contains spec.yaml or the user explicitly names Cladding; ignore ordinary requests in uninitialized…
codeck
Keep Codex as the host. Use Codeck when the user explicitly asks to call Agy/AGY, Antigravity, Gemini, Claude, Kimi, Grok, Codeck, or another configured external executor. These names mean external Codeck executors, never internal Codex subagents. Build a compact task-specific brief, call that specialist, and return…
refactor-safety
A safety checklist for code refactoring, such as extracting components, merging duplicate logic, renaming variables, or reorganizing structure. Refactoring changes code structure without intending to change its behavior.