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 Guild-Agents/guild --skill tddgit clone --depth 1 https://github.com/Guild-Agents/guildWrote 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/guild-agents/guild/tdd)<a href="https://agentmods.dev/skills/guild-agents/guild/tdd"><img src="https://agentmods.dev/badge/skills/guild-agents/guild/tdd/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/guild-agents/guild/tdd"><img src="https://agentmods.dev/badge/skills/guild-agents/guild/tdd.svg" alt="Reviewed on agentmods" width="80" 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 5.1 | $0.00029 | $0.01073 |
| Opus 5.5 | $0.00012 | $0.00429 |
| Sonnet 5.5 | $0.00006 | $0.00215 |
| Haiku 4.5 | $0.00003 | $0.00107 |
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 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 — 160 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development (TDD)
Write the test first. Watch it fail. Write minimal code to pass.
Core principle: If you didn't watch the test fail, you don't know if it tests the right thing.
Usage
/tdd
Invoke this skill before implementing any feature or bugfix. It establishes the discipline for your implementation session.
When to use
- New features
- Bug fixes
- Refactoring
- Behavior changes
Exceptions (ask the user): throwaway prototypes, generated code, configuration files.
The Iron Law
NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST
Write code before the test? Delete it. Start over.
- Don't keep it as "reference"
- Don't "adapt" it while writing tests
- Don't look at it
- Delete means delete
Red-Green-Refactor
RED - Write Failing Test
Write one minimal test showing what should happen.
Requirements:
- One behavior per test
- Clear name that describes behavior
- Real code (no mocks unless unavoidable)
Run the test. Confirm:
- Test fails (not errors)
- Failure message is expected
- Fails because feature missing (not typos)
Test passes? You're testing existing behavior. Fix the test.
GREEN - Minimal Code
Write the simplest code to pass the test.
Don't add features, refactor other code, or "improve" beyond the test.
Run the test. Confirm:
- Test passes
- Other tests still pass
- Output pristine (no errors, warnings)
Test fails? Fix code, not test.
REFACTOR - Clean Up
After green only:
- Remove duplication
- Improve names
- Extract helpers
Keep tests green. Don't add behavior.
Repeat
Next failing test for next behavior.
Good Tests
| Quality | Good | Bad |
|---|---|---|
| Minimal | One thing. "and" in name? Split it. | test('validates email and domain and whitespace') |
| Clear | Name describes behavior | test('test1') |
| Shows intent | Demonstrates desired API | Obscures what code should do |
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 · 160 lines · 29 tokens per session scan A 77ed8c676b86
tdd is a skill published in the GitHub repository Guild-Agents/guild (4 stars, last pushed 3mo ago), licensed MIT. It adds 29 tokens to every session and 1,073 once invoked, about $0.0001 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 2026-08-31.
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