tdd

tdd is a skill for Claude Code, Codex from luisalima/agent-policy-kit. It costs 32 tokens per session (229 once invoked), scanned A, original, MIT.

A test-first coding workflow for changes with behavior that can be checked automatically. It follows the cycle of writing a failing test, making the smallest code change, and checking that the test passes.

In plain words
What is it for?
Use it when adding or changing behavior with a clear contract, such as a function or API response. It is not intended for formatting, documentation-only edits, or exploratory spikes unless the spike is declared first.
Why use it?
It reduces the risk of writing code that does not meet its intended behavior. It also helps catch tests that fail for the wrong reason, such as a typo or missing import.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/luisalima/agent-policy-kit/tdd
Any agent
npx skills add luisalima/agent-policy-kit --skill tdd
Clone the repo
git clone --depth 1 https://github.com/luisalima/agent-policy-kit

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for tdd

README.md
[![agentmods](https://agentmods.dev/badge/skills/luisalima/agent-policy-kit/tdd.svg)](https://agentmods.dev/skills/luisalima/agent-policy-kit/tdd)
Your own site
<a href="https://agentmods.dev/skills/luisalima/agent-policy-kit/tdd"><img src="https://agentmods.dev/badge/skills/luisalima/agent-policy-kit/tdd.svg" alt="Measured on agentmods" height="20"></a>
Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 229 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00032 $0.00229
Opus 5 $0.00016 $0.00114
Sonnet 5 $0.00006 $0.00046
Haiku 4.5 $0.00003 $0.00023

Measured 4d ago against content hash 88abaeb1f6e5, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

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 4d 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.

.agents/skills/tdd/SKILL.md · 26 lines

What it actually says

TDD Discipline

Walk the TDD cycle for the current task:

  1. Identify the behavior to assert. If unclear, ask before proceeding.
  2. Write the failing test first. Show what it asserts and why.
  3. Run the suite. Confirm the new test fails for the right reason, not a typo or import error. If it passes immediately, stop and reassess the test.
  4. Write the minimum source change to make it pass. No extras.
  5. Run the suite again. Confirm green.
  6. Keep the change focused.

Spike Exception

If the behavior is unknown, such as UI layout, an unfamiliar API, or prompt engineering:

  1. Declare the spike up front: Spike to learn X; I will discard and TDD after.
  2. Isolate it from the production change.
  3. Show the discard before the real implementation lands.

An undeclared deviation is skipped tests, not a spike.

Changes

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.

  1. 4d ago First seen · 26 lines · 32 tokens per session scan A 88abaeb1f6e5

Subscribe to this mod's changes

tdd is a skill published in the GitHub repository luisalima/agent-policy-kit (2 stars, last pushed 2mo ago), licensed MIT. It adds 32 tokens to every session and 229 once invoked, about $0.0002 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.