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 mthines/agent-skills --skill tddgit clone --depth 1 https://github.com/mthines/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/mthines/agent-skills/tdd)<a href="https://agentmods.dev/skills/mthines/agent-skills/tdd"><img src="https://agentmods.dev/badge/skills/mthines/agent-skills/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/mthines/agent-skills/tdd"><img src="https://agentmods.dev/badge/skills/mthines/agent-skills/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 | $0.00078 | $0.01987 |
| Opus 5.5 | $0.00031 | $0.00795 |
| Sonnet 5.5 | $0.00016 | $0.00397 |
| Haiku 4.5 | $0.00008 | $0.00199 |
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 today.
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 — 167 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development
Enforce strict RED-GREEN-REFACTOR discipline. One test at a time. Tests describe WHAT the system does, never HOW.
Lens-eligible for the pr-reviewer agent: lens.md auto-loads when a diff changes tests.
Input
Check $ARGUMENTS for the feature or behavior description.
- If
$ARGUMENTScontains a feature description, use it directly. - If
$ARGUMENTSstarts withprovenance, run only the provenance check on the named or changed test files. Seerules/test-provenance.md. - If
$ARGUMENTScontains "after" (e.g.,/tdd after), run in Test-After Mode — write tests for existing code. Seerules/test-after.md. - If
$ARGUMENTSis empty, ask the user what behavior they want to implement or test.
Step 0: Discover Project Test Setup
Before writing any tests:
- Find existing tests — glob for
**/*.test.*,**/*.spec.*,**/*_test.*,**/test_*.*,**/tests/**to identify the test framework, naming conventions, and directory structure. - Find the test runner — check
package.jsonscripts,Makefile,pyproject.toml,Cargo.toml,go.mod, or similar for the test command. - Adopt existing patterns — match the project's test style exactly: same imports, same assertion library, same file naming, same directory placement. Never introduce a new test framework or pattern.
- Identify the run command — store it mentally as
TEST_CMDfor use throughout the cycle. If you can run a single test file or test case, prefer that over the full suite.
If no tests exist yet, ask the user which framework to use before proceeding.
Step 1: Prioritize by Business Criticality
Before diving into implementation, identify what matters most:
- Core user flows first — what are the primary actions users perform? Test those before edge cases.
- Ask if unclear — if the feature has multiple behaviors, ask the user to rank them or list the critical paths.
- Build a test list — write a numbered list of behaviors to test, ordered by importance. Each item should be a single, specific behavior (not "test the login flow" but "reject login with expired password").
What ships with it
6 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.
- today Changed · +2 lines aa2f6c92c816
- 9d ago Changed · -5 lines · -79 tokens per session c935f1a201a4
- 2mo ago First seen · 170 lines · 157 tokens per session scan A e7e7def06faf
tdd is a skill published in the GitHub repository mthines/agent-skills (20 stars, last pushed today), licensed MIT. It adds 78 tokens to every session and 1,987 once invoked, about $0.0003 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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