Borrowing it
Nothing to install: this file belongs to stevesolun/ctx. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/stevesolun/ctx/main/.agents/skills/tdd/SKILL.mdgit clone --depth 1 https://github.com/stevesolun/ctxWrote 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/stevesolun/ctx/tdd)<a href="https://agentmods.dev/skills/stevesolun/ctx/tdd"><img src="https://agentmods.dev/badge/skills/stevesolun/ctx/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/stevesolun/ctx/tdd"><img src="https://agentmods.dev/badge/skills/stevesolun/ctx/tdd.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00039 | $0.00348 |
| Opus 5.5 | $0.00016 | $0.00139 |
| Sonnet 5.5 | $0.00008 | $0.00070 |
| Haiku 4.5 | $0.00004 | $0.00035 |
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.
What it actually says
Test-Driven Development
Use small red → green → refactor cycles when a test-first feedback loop is practical. Treat repository conventions, existing tests, and the requested behavior as authoritative.
Loop
- Identify one observable behavior and the seam through which callers see it.
- Write the smallest meaningful test and confirm that it fails for the expected reason.
- Add only enough implementation to make the test pass.
- Refactor when doing so improves clarity or design; keep the suite green.
- Repeat with the next vertical slice.
Infer seams from public interfaces and nearby tests. Ask the user only when choosing a seam would materially change the product contract, cost, or scope.
Judgment
- Prefer behavior-focused tests that survive internal refactors.
- Derive expected results from a specification, worked example, or other independent source rather than duplicating the implementation.
- Mock external or nondeterministic boundaries when useful; follow established repository patterns where they provide an adequate feedback loop.
- Prefer vertical slices over a speculative batch of tests. Batch closely related mechanical cases when that is clearer and faster.
- If a failing-first cycle is impractical—for example in legacy code with no usable seam—state the limitation and establish the nearest reliable characterization or integration test.
Read tests.md for examples and mocking.md when deciding whether and where to use test doubles.
What ships with it
3 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.
- 1mo ago First seen · 39 lines · 39 tokens per session scan A 2d2418a666ff
tdd is a skill published in the GitHub repository stevesolun/ctx (589 stars, last pushed 11d ago), licensed MIT. It adds 39 tokens to every session and 348 once invoked, about $0.0002 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 2026-08-30.
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