Agent skill

TDD

Test-driven development - write failing test first, then minimal code.

MITAuto-check passedTesting & QA

Install TDD

skills CLI

$ npx skills add itseffi/agentic-os --skill tdd -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install itseffi/agentic-os tdd --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/itseffi/agentic-os.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/tdd .claude/skills/tdd && rm -rf skills-src

Use ~/.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/

Paste into Claude Code

Install the "tdd" agent skill from https://github.com/itseffi/agentic-os/tree/main/.agents/skills/tdd into .claude/skills/tdd/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "tdd", 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

$skill-installer install https://github.com/itseffi/agentic-os/tree/main/.agents/skills/tdd

Type 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.

skills CLI

$ npx skills add itseffi/agentic-os --skill tdd -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install itseffi/agentic-os tdd --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/itseffi/agentic-os.git skills-src && mkdir -p .agents/skills && cp -r skills-src/.agents/skills/tdd .agents/skills/tdd && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "tdd" agent skill from https://github.com/itseffi/agentic-os/tree/main/.agents/skills/tdd into .agents/skills/tdd/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "tdd", 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.

skills CLI

$ npx skills add itseffi/agentic-os --skill tdd -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install itseffi/agentic-os tdd --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/itseffi/agentic-os.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/.agents/skills/tdd .cursor/skills/tdd && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "tdd" agent skill from https://github.com/itseffi/agentic-os/tree/main/.agents/skills/tdd into .cursor/skills/tdd/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "tdd", 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

$ gemini skills install https://github.com/itseffi/agentic-os.git --path .agents/skills/tdd

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add itseffi/agentic-os --skill tdd -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install itseffi/agentic-os tdd --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/itseffi/agentic-os.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/.agents/skills/tdd .gemini/skills/tdd && rm -rf skills-src

Use ~/.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/

Paste into Gemini CLI

Install the "tdd" agent skill from https://github.com/itseffi/agentic-os/tree/main/.agents/skills/tdd into .gemini/skills/tdd/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "tdd", 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.

GitHub CLI

$ gh skill install itseffi/agentic-os tdd

Installs 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).

skills CLI

$ npx skills add itseffi/agentic-os --skill tdd -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/itseffi/agentic-os.git skills-src && mkdir -p .github/skills && cp -r skills-src/.agents/skills/tdd .github/skills/tdd && rm -rf skills-src

Use ~/.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/

Paste into GitHub Copilot

Install the "tdd" agent skill from https://github.com/itseffi/agentic-os/tree/main/.agents/skills/tdd into .github/skills/tdd/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "tdd", 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.

skills CLI

$ npx skills add itseffi/agentic-os --skill tdd -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install itseffi/agentic-os tdd --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/itseffi/agentic-os.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/.agents/skills/tdd .opencode/skills/tdd && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "tdd" agent skill from https://github.com/itseffi/agentic-os/tree/main/.agents/skills/tdd into .opencode/skills/tdd/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "tdd", 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: tdd
GitHub stars: 115
Token cost: ~732 tokens
SKILL.md length: 386 words
Files: 2
Skills in repo: 29
Repo updated: Oct 7, 2026
First seen: Oct 7, 2026
Licence: MIT

At a glance

Test-driven development - write failing test first, then minimal code.

Tasks that involve Test-driven development
SKILL.md covers The Iron Law, Red-Green-Refactor, Why Order Matters and Red Flags - STOP and Start Over, plus 4 more sections
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

TDD is an agent skill from itseffi/agentic-os. Test-driven development - write failing test first, then minimal code. Use before implementing any feature or bugfix.

Its SKILL.md is about 730 tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files (for example `agents/openai.yaml`).

It sits in Testing & QA, covering Test-driven development. The repository describes itself as: Agentic personal OS to automate high-leverage workflows with Codex, Claude Code, Pi, OpenClaw and other coding agents/ runtime platforms. The licence is MIT.

When your agent uses it

Tasks that involve Test-driven development

Example prompts

“/tdd”

What it can do on your machine

Read from SKILL.md and the folder at commit e54d0ac. 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

TDD loads about 732 tokens when it runs. Until then it costs about 30 tokens; SKILL.md has 386 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~30
When it runs · the whole SKILL.md, loaded when a task matches: ~732

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 itseffi/agentic-os at commit e54d0ac, republished under its MIT licence (© itseffi). 386 words, ~732 tokens.

Download SKILL.mdSave it as .claude/skills/tdd/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.

name: tdd
description: Test-driven development - write failing test first, then minimal code. Use before implementing any feature or bugfix.

Test-Driven Development (TDD)

Use when implementing any feature or bugfix, before writing implementation code.

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST

Write code before the test? Delete it. Start over.

No exceptions:

Don't keep it as "reference"
Don't "adapt" it while writing tests
Delete means delete

Red-Green-Refactor

RED - Write Failing Test

Write one minimal test showing what should happen.

One behavior
Clear name
Real code (no mocks unless unavoidable)

Verify RED - Watch It Fail

MANDATORY. Never skip.

Run the test, confirm it fails (not errors)
Failure message is expected
Test passes? You're testing existing behavior. Fix test.

GREEN - Minimal Code

Write simplest code to pass the test.

Just enough to pass
No extra features
Don't add behavior beyond the test

Verify GREEN - Watch It Pass

MANDATORY.

Test passes
Other tests still pass
Output pristine (no errors, warnings)

REFACTOR - Clean Up

After green only:

Remove duplication
Improve names
Extract helpers Keep tests green. Don't add behavior.

Why Order Matters

"I'll write tests after" Tests written after pass immediately. Passing immediately proves nothing. Test-first forces you to see the test fail, proving it actually tests something.

"Tests after achieve same goals" No. Tests-after answer "What does this do?" Tests-first answer "What should this do?"

"Deleting X hours of work is wasteful" Sunk cost fallacy. The time is gone. The waste is keeping code you can't trust.

Show full SKILL.md (166 more words)Show less

Red Flags - STOP and Start Over

Code before test
Test after implementation
Test passes immediately
"I already manually tested it"
"Tests after achieve the same purpose"
"This is different because..."

All mean: Delete code. Start over with TDD.

Common Rationalizations

Excuse	Reality
"Too simple to test"	Simple code breaks. Test takes 30 seconds.
"I'll test after"	Tests passing immediately prove nothing.
"Already manually tested"	Ad-hoc ≠ systematic. No record, can't re-run.
"TDD will slow me down"	TDD faster than debugging later.

Verification Checklist

Before marking work complete:

Every new function/method has a test
Watched each test fail before implementing
Each test failed for expected reason
Wrote minimal code to pass each test
All tests pass
Output pristine (no errors, warnings)

Can't check all boxes? You skipped TDD. Start over.

When to Use

Use this skill when the task directly matches the workflow described above.

When Not to Use

Do not use this skill when the request is unrelated, low-stakes, or better handled by a simpler direct response.

Files

SKILL.md and 1 other file in .agents/skills/tdd of itseffi/agentic-os.

SKILL.md
agents/openai.yaml

Open the folder on GitHubat commit e54d0ac

Compare with similar skills

TDD 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.

TDD compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
TDD this skillitseffi/agentic-os	115	—	~732	Automated safety check: Pass	MIT	yesterday
TDDpietheinstrengholt/rssmonster	564	30 repos	~906	Automated safety check: Pass	MIT	yesterday
TDD WorkflowhellangleZ/burn-in-cceverywhere-ralph	112	11 repos	~2.4k	Automated safety check: Pass	None	8 mo ago
TDDsanity-io/sanity	6.4k	20 repos	~1k	Automated safety check: Pass	MIT	today
Test Driven Developmentfarm-fe/farm	5.6k	51 repos	~2.5k	Automated safety check: Pass	MIT	16 days ago
Tapd Story PipelineTencentBlueKing/bk-bcs	840	—	~2.6k	Automated safety check: Pass	Custom licence	today

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Questions about TDD

What does TDD do?

Test-driven development - write failing test first, then minimal code. TDD is an agent skill from itseffi/agentic-os. Test-driven development - write failing test first, then minimal code.

When should I use TDD?

TDD fits situations like: tasks that involve Test-driven development.

How do I install TDD in Claude Code?

Run `npx skills add itseffi/agentic-os --skill tdd -a claude-code`. Or copy the skill folder (.agents/skills/tdd in itseffi/agentic-os) into .claude/skills/tdd in your project. Claude Code loads it when a task matches its description.

How do I install TDD in Codex?

Run `npx skills add itseffi/agentic-os --skill tdd -a codex`. Or copy the skill folder (.agents/skills/tdd in itseffi/agentic-os) into .agents/skills/tdd in your project. Codex loads it when a task matches its description.

Can I use TDD 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 itseffi/agentic-os --skill tdd -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/tdd, .gemini/skills/tdd, .github/skills/tdd and .opencode/skills/tdd in your project.

What does TDD need to run?

SKILL.md names no scripts, command-line tools or credentials: TDD is instructions for the agent only.

Does TDD 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 TDD 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 TDD use?

TDD 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 TDD use?

About 732 tokens (SKILL.md is roughly 2.9k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to TDD?

Skills that share tags, products or a category with TDD: TDD (pietheinstrengholt/rssmonster, 564 stars), TDD Workflow (hellangleZ/burn-in-cceverywhere-ralph, 112 stars), TDD (sanity-io/sanity, 6.4k stars) and Test Driven Development (farm-fe/farm, 5.6k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains TDD?

itseffi (a GitHub user) maintains it in itseffi/agentic-os, which has 115 GitHub stars. The repository holds 29 skills in this directory. The repository was last updated on October 7, 2026.

Source: itseffi/agentic-os on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install TDD

Facts

At a glance

What it does

When your agent uses it

Example prompts

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Test-Driven Development (TDD)

The Iron Law

Red-Green-Refactor

RED - Write Failing Test

Verify RED - Watch It Fail

GREEN - Minimal Code

Verify GREEN - Watch It Pass

REFACTOR - Clean Up

Why Order Matters

Red Flags - STOP and Start Over

Common Rationalizations

Verification Checklist

When to Use

When Not to Use

Files

Compare with similar skills

Similar skills

More from itseffi/agentic-os

Related

Questions about TDD