addyosmani/agent-skills is a collection of reusable workflows, quality checks, commands, and other instructions that guide AI coding agents through software development. It is for developers who want agents to follow consistent engineering practices, and the catalogue entries are its packaged skills, commands, agents, plugins, instructions, and hooks.
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 agentmods add skills/addyosmani/agent-skills/test-driven-developmentnpx skills add addyosmani/agent-skills --skill test-driven-developmentgit clone --depth 1 https://github.com/addyosmani/agent-skillsWrote 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/addyosmani/agent-skills/test-driven-development)<a href="https://agentmods.dev/skills/addyosmani/agent-skills/test-driven-development"><img src="https://agentmods.dev/badge/skills/addyosmani/agent-skills/test-driven-development.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00050 | $0.03721 |
| Opus 5 | $0.00025 | $0.01861 |
| Sonnet 5 | $0.00010 | $0.00744 |
| Haiku 4.5 | $0.00005 | $0.00372 |
Grade A, and why
test-driven-development 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 5d 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.
Copies of this mod
8 near-identical copies found in the catalogue:
- test-driven-development — 100% identical, 2 lines differ
- test-driven-development — 98% identical, 1 lines differ
- test-driven-development — 98% identical, 7 lines differ
- test-driven-development — 88% identical, 70 lines differ
- addyosmani-tdd — 88% identical, 26 lines differ
- test-driven-development — 86% identical, 29 lines differ
- test-driven-development — 84% identical, 19 lines differ
- test-driven-development — 84% identical, 19 lines differ
How it starts
The opening of the file, as written. The whole thing — 399 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development
Overview
Write a failing test before writing the code that makes it pass. For bug fixes, reproduce the bug with a test before attempting a fix. Tests are proof — "seems right" is not done. A codebase with good tests is an AI agent's superpower; a codebase without tests is a liability.
When to Use
- Implementing any new logic or behavior
- Fixing any bug (the Prove-It Pattern)
- Modifying existing functionality
- Adding edge case handling
- Any change that could break existing behavior
When NOT to use: Pure configuration changes, documentation updates, or static content changes that have no behavioral impact.
Related: For browser-based changes, combine TDD with runtime verification using Chrome DevTools MCP — see the Browser Testing section below.
Discover the Stack First
The TDD cycle is universal; the commands are not. Before writing the first test, discover how this repository tests, and use its commands for every RED, GREEN, and verification step:
- Language and build system —
package.json,pom.xml/build.gradle,pyproject.toml,go.mod,Cargo.toml,Gemfile, aMakefile - Checked-in wrappers — prefer
./gradlew,./mvnw,make test, or a repo script over globally installed tools - Test framework and configuration — and how it runs a single focused test vs the full suite
- Existing conventions — where tests live, how files are named, what patterns neighboring tests follow
- Documented commands — README, CONTRIBUTING, and CI workflows show the commands that actually gate merges
Run the repository's focused-test command during the loop and its full-suite command before completion. Never assume a default like npm test — a Gradle, Cargo, or pytest project has its own equivalent.
The examples below use TypeScript for illustration; the workflow is identical in any language once you've discovered the project's own tooling.
The TDD Cycle
RED GREEN REFACTOR
Write a test Write minimal code Clean up the
that fails ──→ to make it pass ──→ implementation ──→ (repeat)
│ │ │
▼ ▼ ▼
Test FAILS Test PASSES Tests still PASS
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.
- 5d ago First seen · 399 lines · 50 tokens per session scan A 440fb3c9b76f
test-driven-development is a skill published in the GitHub repository addyosmani/agent-skills (91,974 stars, last pushed yesterday), licensed MIT. It adds 50 tokens to every session and 3,721 once invoked, about $0.0003 per session on Opus 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
test-driven-development
Drives development with tests via Red-Green-Refactor and the Prove-It pattern, with hard rules against weakening assertions or faking green suites. Use when implementing any logic, fixing any bug, or changing any behavior. Triggers on "add a feature", "fix this bug", "write tests", or any task where done must be…
spec-driven-development
Creates specs before coding, with hard rules against silently filled assumptions and untestable success criteria. Use when starting a new project, feature, or significant change and no specification exists yet. Triggers on "build me", "create a", "add a feature", or any requirement vague enough to need interpretation.
test-driven-development
用测试驱动开发。用于实现任何逻辑、修复任何 bug，或改变任何行为。用于需要证明代码能工作、收到 bug 报告，或即将修改现有功能时。.
test-driven-development
Red-green-refactor cycle with meaningful coverage. Tests are written before implementation. Coverage is a side effect of good tests, not the goal.
writing-skills
当创建新技能、编辑现有技能或在部署前验证技能是否有效时使用.
skillshare-implement-feature
Implement a feature from a spec file or description using TDD workflow. Use this skill whenever the user asks to: add a new CLI command, implement a feature from a spec, build new functionality, add a flag, create a new internal package, or write Go code for skillshare. This skill enforces test-first development…