Agent skill

TDD

TDD with red-green-refactor loop and vertical slices. An agent skill from softspark/ai-toolkit.

Apache-2.0Auto-check: notesTesting & QA

Install TDD

skills CLI

$ npx skills add softspark/ai-toolkit --skill tdd -a claude-code

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

GitHub CLI

$ gh skill install softspark/ai-toolkit 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/softspark/ai-toolkit.git skills-src && mkdir -p .claude/skills && cp -r skills-src/app/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/softspark/ai-toolkit/tree/main/app/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/softspark/ai-toolkit/tree/main/app/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 softspark/ai-toolkit --skill tdd -a codex

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

GitHub CLI

$ gh skill install softspark/ai-toolkit 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/softspark/ai-toolkit.git skills-src && mkdir -p .agents/skills && cp -r skills-src/app/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/softspark/ai-toolkit/tree/main/app/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 softspark/ai-toolkit --skill tdd -a cursor

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

GitHub CLI

$ gh skill install softspark/ai-toolkit 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/softspark/ai-toolkit.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/app/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/softspark/ai-toolkit/tree/main/app/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/softspark/ai-toolkit.git --path app/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 softspark/ai-toolkit --skill tdd -a gemini-cli

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

GitHub CLI

$ gh skill install softspark/ai-toolkit 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/softspark/ai-toolkit.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/app/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/softspark/ai-toolkit/tree/main/app/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 softspark/ai-toolkit 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 softspark/ai-toolkit --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/softspark/ai-toolkit.git skills-src && mkdir -p .github/skills && cp -r skills-src/app/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/softspark/ai-toolkit/tree/main/app/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 softspark/ai-toolkit --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 softspark/ai-toolkit 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/softspark/ai-toolkit.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/app/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/softspark/ai-toolkit/tree/main/app/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: 179
Token cost: ~1.4k tokens
SKILL.md length: 604 words
Files: 6
Skills in repo: 112
Repo updated: Oct 7, 2026
First seen: Oct 7, 2026
Licence: Apache-2.0

At a glance

TDD with red-green-refactor loop and vertical slices. An agent skill from softspark/ai-toolkit.

Works in 4 steps: Planning → Tracer Bullet → Incremental Loop → …
Tasks that involve Test-driven development
SKILL.md covers Usage, The Iron Law, Philosophy and Anti-Pattern: Horizontal Slices, plus 7 more sections
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

TDD is an agent skill from softspark/ai-toolkit. TDD with red-green-refactor loop and vertical slices. Triggers: TDD, test-first, red-green-refactor, test driving development.

Its SKILL.md is about 1.4k tokens, which your agent loads only when the skill is triggered. The skill folder holds 6 other files (for example `reference/deep-modules.md`, `reference/interface-design.md` and `reference/mocking.md`).

It sits in Testing & QA, covering Test-driven development. The repository describes itself as: Professional-grade AI coding toolkit: 94 skills, 44 agents, multi-platform (Claude, Cursor, Windsurf, Copilot, Gemini, Cline, Roo Code, Aider, Augment, Antigravity, Codex CLI… The licence is Apache-2.0.

When your agent uses it

Tasks that involve Test-driven development

Example prompts

“/tdd”

Requirements

Pre-approved tools (allowed-tools): Read, Write, Edit, Grep, Glob, Bash, Agent

Workflow steps

4 steps, taken from the step headings in SKILL.md.

Planning
Tracer Bullet
Incremental Loop
Refactor

What it can do on your machine

Read from SKILL.md and the folder at commit d64db2b. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves these tools, so the agent can use them without asking each time:
- Read
- Write
- Edit
- Grep
- Glob
- Bash
- Agent
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 1.4k tokens when it runs. Until then it costs about 33 tokens; SKILL.md has 604 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~33
When it runs · the whole SKILL.md, loaded when a task matches: ~1.4k

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: notes

The automated check noted patterns worth knowing about, such as sudo or a known installer.

NotePre-approves every shell command (allowed-tools: Bash)SKILL.md
```
allowed-tools: Read, Write, Edit, Grep, Glob, Bash, Agent
```

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 softspark/ai-toolkit at commit d64db2b, republished under its Apache-2.0 licence (© softspark). 604 words, ~1,412 tokens.

Download SKILL.mdSave it as .claude/skills/tdd/SKILL.md (or your agent's skills folder). This skill also uses 5 other files; get the full folder from GitHub.

name: tdd
description: TDD with red-green-refactor loop and vertical slices. Triggers: TDD, test-first, red-green-refactor, test driving development.
allowed-tools: Read, Write, Edit, Grep, Glob, Bash, Agent
user-invocable: true
effort: high
argument-hint: [feature or behavior to implement]

Test-Driven Development

$ARGUMENTS

Build features using strict RED → GREEN → REFACTOR cycles with vertical slices.

Usage

/tdd [feature or behavior to implement]

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
Don't look at it
Delete means delete

Implement fresh from tests. Period.

Violating the letter of this rule is violating the spirit of this rule.

Philosophy

Core principle: Tests verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't.

Good tests: Integration-style, exercise real code paths through public APIs. Describe what the system does, not how. Read like specifications. Survive refactors.

Bad tests: Coupled to implementation. Mock internal collaborators, test private methods, verify through external means. Warning sign: test breaks on refactor but behavior is unchanged.

See reference/tests.md for examples, reference/mocking.md for mocking guidelines.

Anti-Pattern: Horizontal Slices

DO NOT write all tests first, then all implementation.

WRONG (horizontal):
  RED:   test1, test2, test3, test4, test5
  GREEN: impl1, impl2, impl3, impl4, impl5

RIGHT (vertical):
  RED→GREEN: test1→impl1
  RED→GREEN: test2→impl2
  RED→GREEN: test3→impl3

Tests written in bulk test imagined behavior. Vertical slices let each test respond to what you learned from the previous cycle.

Workflow

1. Planning

Before writing any code:

Confirm with user what interface changes are needed
Confirm which behaviors to test (prioritize — you can't test everything)
Identify opportunities for deep modules
Design interfaces for testability
List behaviors to test (not implementation steps)
Get user approval

2. Tracer Bullet

Write ONE test that confirms ONE thing:

RED:   Write test for first behavior → test fails
GREEN: Write minimal code to pass → test passes

This proves the path works end-to-end.

3. Incremental Loop

For each remaining behavior:

RED:   Write next test → fails
GREEN: Minimal code to pass → passes

Rule	Description
One at a time	One test per cycle
Minimal	Only enough code to pass current test
No anticipation	Don't code for future tests
Behavioral	Tests focus on observable behavior

4. Refactor

After all tests pass, look for refactor candidates:

Extract duplication
Deepen modules (complexity behind simple interfaces)
Apply SOLID where natural
Run tests after each refactor step

Never refactor while RED. Get to GREEN first.

Checklist Per Cycle

[ ] Test describes behavior, not implementation
[ ] Test uses public interface only
[ ] Test would survive internal refactor
[ ] Code is minimal for this test
[ ] No speculative features added

Rules

One RED→GREEN cycle at a time — never batch
Tests assert on observable outcomes, not internal state
Mock only at system boundaries (see reference/mocking.md)
Each cycle leaves the codebase in a working state

Show full SKILL.md (263 more words)Show less

Red Flags — STOP and Start Over

If you catch yourself doing ANY of these, delete the code and restart with TDD:

Writing production code before a failing test
Writing tests after implementation
Test passes immediately (you're testing existing behavior — fix the test)
Can't explain why the test failed
Tests added "later"
Rationalizing "just this once"
"I already manually tested it"
"Keep as reference" or "adapt existing code"

Common Rationalizations

Excuse	Reality
"Too simple to test"	Simple code breaks. Test takes 30 seconds.
"I'll test after"	Tests passing immediately prove nothing.
"Tests after achieve same goals"	Tests-after = "what does this do?" Tests-first = "what should this do?"
"Already manually tested"	Ad-hoc ≠ systematic. No record, can't re-run.
"Deleting X hours is wasteful"	Sunk cost fallacy. Keeping unverified code is technical debt.
"Need to explore first"	Fine. Throw away exploration, start with TDD.
"TDD will slow me down"	TDD faster than debugging. Pragmatic = test-first.
"This is different because..."	No. Apply the Iron Law.

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 (feature missing, not typo)
Wrote minimal code to pass each test
All tests pass
Output pristine (no errors, warnings)
Tests use real code (mocks only at system boundaries)
Edge cases and errors covered

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

Feature complete? → /review to get a code review
Need to plan the feature first? → /plan for task breakdown
Want a full test coverage sweep? → /workflow test-coverage
Debugging a test failure? → /debug for systematic root cause analysis

Files

SKILL.md and 5 other files in app/skills/tdd of softspark/ai-toolkit.

SKILL.md
reference/deep-modules.md
reference/interface-design.md
reference/mocking.md
reference/refactoring.md
reference/tests.md

Open the folder on GitHubat commit d64db2b

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 skillsoftspark/ai-toolkit	179	—	~1.4k	Automated safety check: Notes	Apache-2.0	today
TDDfossasia/eventyay-interpretation	1.6k	28 repos	~1.1k	Automated safety check: Pass	Apache-2.0	2 days ago
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	49 repos	~2.5k	Automated safety check: Pass	MIT	15 days ago
Tapd Story PipelineTencentBlueKing/bk-bcs	840	—	~2.6k	Automated safety check: Pass	Custom licence	13 days ago

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Questions about TDD

What does TDD do?

TDD with red-green-refactor loop and vertical slices. An agent skill from softspark/ai-toolkit. TDD is an agent skill from softspark/ai-toolkit. TDD with red-green-refactor loop and vertical slices.

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 softspark/ai-toolkit --skill tdd -a claude-code`. Or copy the skill folder (app/skills/tdd in softspark/ai-toolkit) 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 softspark/ai-toolkit --skill tdd -a codex`. Or copy the skill folder (app/skills/tdd in softspark/ai-toolkit) 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 softspark/ai-toolkit --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. Its frontmatter pre-approves these tools: Read, Write, Edit, Grep, Glob, Bash, Agent.

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 notes only (pre-approves every shell command (allowed-tools: bash)), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.

What licence does TDD use?

TDD is published under the Apache-2.0 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 1.4k tokens (SKILL.md is roughly 5.6k 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 (fossasia/eventyay-interpretation, 1.6k 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?

softspark (a GitHub user) maintains it in softspark/ai-toolkit, which has 179 GitHub stars. The repository holds 112 skills in this directory. The repository was last updated on October 7, 2026.

Source: softspark/ai-toolkit 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

Requirements

Workflow steps

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Test-Driven Development

Usage

The Iron Law

Philosophy

Anti-Pattern: Horizontal Slices

Workflow

1. Planning

2. Tracer Bullet

3. Incremental Loop

4. Refactor

Checklist Per Cycle

Rules

Red Flags — STOP and Start Over

Common Rationalizations

Verification Checklist

Related Skills

Files

Compare with similar skills

Similar skills

More from softspark/ai-toolkit

Related

Questions about TDD