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/ethansei/skills/tddnpx skills add EthanSei/skills --skill tddgit clone --depth 1 https://github.com/EthanSei/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/ethansei/skills/tdd)<a href="https://agentmods.dev/skills/ethansei/skills/tdd"><img src="https://agentmods.dev/badge/skills/ethansei/skills/tdd.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 | $0.00093 | $0.01196 |
| Opus 5 | $0.00046 | $0.00598 |
| Sonnet 5 | $0.00019 | $0.00239 |
| Haiku 4.5 | $0.00009 | $0.00120 |
Grade A, and why
tdd 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.
How it starts
The opening of the file, as written. The whole thing — 144 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development
Write the test first. Make it pass. Clean up. Run the tests. Every time.
The Cycle
Every code change follows red-green-refactor:
- Red — Write a test for the next behavior. Run it. Watch it fail.
- Green — Write the minimum code to make the test pass. Nothing more.
- Refactor — Clean up duplication and improve clarity. Tests stay green.
- Repeat — Pick the next behavior. Start another cycle.
Run tests after every step. Not just at the end — after every step.
1. Start With a Failing Test
Before writing any implementation, write a test that:
- Describes one specific behavior or requirement
- Fails for the right reason (missing function, wrong return value — not a syntax error)
- Uses clear, descriptive names that read as specifications
Do not write multiple tests at once. One test, one behavior, one cycle.
2. Write the Minimum to Pass
Make the failing test pass with the simplest code that works. Do not:
- Handle edge cases you haven't tested yet
- Build abstractions before you have three examples
- Add error handling for scenarios not covered by a test
- Optimize before the behavior is correct
If you're writing code that no test exercises, stop. Write the test first.
3. Refactor Under Green Tests
After the test passes, improve the code while keeping tests green:
- Extract common patterns only when you see real duplication
- Rename for clarity
- Simplify complex conditionals
- Remove dead code
Run tests after each refactoring move. If any test turns red, undo and try a smaller change.
4. Run Tests After Every Change
This is not optional. Run the relevant test suite:
- After writing a new test (confirm it fails)
- After writing implementation (confirm it passes)
- After every refactoring move
- Before considering any task done
If you cannot run tests (no test runner configured, unfamiliar project), tell the user and ask how to run them. Do not skip testing and move on silently.
5. Discover the Test Runner
What ships with it
2 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.
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 · 144 lines · 93 tokens per session scan A 5cff26499e18
tdd is a skill published in the GitHub repository EthanSei/skills (2 stars, last pushed 6mo ago), licensed MIT. It adds 93 tokens to every session and 1,196 once invoked, about $0.0005 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 2026-08-31.
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tdd
Test-driven development. Use when the user wants to build features or fix bugs test-first, mentions "red-green-refactor", or wants integration tests.
strict-tdd
Strict RED->GREEN->REFACTOR test-driven development with enforcement. Never write production code before a failing test. Atomic commits per TDD cycle.
tdd
This skill should be used when the user wants to implement features or fix bugs using test-driven development. Enforces the RED-GREEN-REFACTOR cycle with vertical slicing, context isolation between test writing and implementation, human checkpoints, and auto-test feedback loops. Uses multi-agent orchestration with the…
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Execute tasks from a track's implementation plan following TDD workflow.