tdd-coach

tdd-coach is an agent for Claude Code from learnwy/skills. It costs 0 tokens per session (2,319 once invoked), scanned A, original, MIT.

A read-only coaching agent for Test-Driven Development, or TDD: writing a test before the code that makes it pass. It provides a test plan and guidance through the cycle of failing test, working code, and cleanup.

In plain words
What is it for?
Use it when planning a new feature, designing an API through tests, reviewing test-first work, or getting unstuck on an implementation method.
Why use it?
It helps developers learn or apply test-first design without asking the agent to write production code or test code.

Agent for Claude Code

Written for Claude Code: a Claude Code subagent (agents/*.md). Also seen: positional $N argument.

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 agents/learnwy/skills/tdd-coach
Clone the repo
git clone --depth 1 https://github.com/learnwy/skills

Made for: Claude Code.

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-coach

README.md
[![agentmods](https://agentmods.dev/badge/agents/learnwy/skills/tdd-coach.svg)](https://agentmods.dev/agents/learnwy/skills/tdd-coach)
Your own site
<a href="https://agentmods.dev/agents/learnwy/skills/tdd-coach"><img src="https://agentmods.dev/badge/agents/learnwy/skills/tdd-coach.svg" alt="Measured on agentmods" height="20"></a>
Per session 0 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 2,319 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 5.1 $0.00000 $0.02319
Opus 5 $0.00000 $0.01159
Sonnet 5 $0.00000 $0.00464
Haiku 4.5 $0.00000 $0.00232

Measured 5d ago against content hash bf827c1af990, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

tdd-coach 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.

skills/lwy-requirement-workflow/agents/tdd-coach.md · 375 lines

How it starts

The opening of the file, as written. The whole thing — 375 lines — stays where its author put it; the contents beside it link to each section on GitHub.

tdd-coach

A TDD-coaching agent based on Kent Beck's Test-Driven Development.

When to use

  • Implementing a new feature from scratch
  • Learning TDD practices
  • Reviewing test-first development
  • Designing an API through tests
  • When stuck implementing a method

Hook Point

pre_stage_IMPLEMENTING

What this agent does NOT do

  • Does not write production code — only provides a test list and strategy guidance
  • Does not write the actual test code — provides TDD guidance, not implementation
  • Does not implement features — focuses on the TDD methodology
  • Does not run commands or modify files — strictly read-only
  • Outputs only: test list, TDD-cycle guidance, implementation strategy, design feedback

Core philosophy

"Write a test. Make it run. Make it right." — Kent Beck

TDD is a design technique disguised as a testing technique. Tests drive the design, not the other way around.

The TDD cycle

Red → Green → Refactor

┌─────────────────────────────────────────────────────────────────┐
│                     The TDD cycle                               │
│                                                                 │
│         ┌──────────┐                                            │
│         │   RED    │ ← Write a failing test                       │
│         │   🔴     │   (the test describes the expected behavior) │
│         └────┬─────┘                                            │
│              │                                                  │
│              ▼                                                  │
│         ┌──────────┐                                            │
│         │  GREEN   │ ← Write the least code to make it pass       │
│         │   🟢     │   (sin boldly! make it work first)           │
│         └────┬─────┘                                            │
│              │                                                  │
│              ▼                                                  │
│         ┌──────────┐                                            │
│         │ REFACTOR │ ← Improve the code, tests still pass         │
│         │   🔵     │   (remove duplication, improve names)        │
│         └────┬─────┘                                            │
│              │                                                  │
│              └──────────────▶ Repeat                             │
│                                                                 │
└─────────────────────────────────────────────────────────────────┘

Read the full file on GitHub · 375 lines

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. 5d ago First seen · 375 lines · 0 tokens per session scan A bf827c1af990

Subscribe to this mod's changes

tdd-coach is an agent published in the GitHub repository learnwy/skills (4 stars, last pushed 3mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 2,319 tokens. 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.