TDD
pietheinstrengholt/rssmonster
Test-driven development. An agent skill from pietheinstrengholt/rssmonster.
A skill your agent uses when implementing any feature or fix using TDD, before writing any implementation code
Install Red Synthesize Green
$ npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install SebastienDegodez/copilot-instructions red-synthesize-green --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/SebastienDegodez/copilot-instructions.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/superpowers-whetstone/skills/red-synthesize-green .claude/skills/red-synthesize-green && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "red-synthesize-green" agent skill from https://github.com/SebastienDegodez/copilot-instructions/tree/main/plugins/superpowers-whetstone/skills/red-synthesize-green into .claude/skills/red-synthesize-green/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "red-synthesize-green", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/SebastienDegodez/copilot-instructions/tree/main/plugins/superpowers-whetstone/skills/red-synthesize-greenType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install SebastienDegodez/copilot-instructions red-synthesize-green --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/SebastienDegodez/copilot-instructions.git skills-src && mkdir -p .agents/skills && cp -r skills-src/plugins/superpowers-whetstone/skills/red-synthesize-green .agents/skills/red-synthesize-green && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "red-synthesize-green" agent skill from https://github.com/SebastienDegodez/copilot-instructions/tree/main/plugins/superpowers-whetstone/skills/red-synthesize-green into .agents/skills/red-synthesize-green/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "red-synthesize-green", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install SebastienDegodez/copilot-instructions red-synthesize-green --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/SebastienDegodez/copilot-instructions.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/plugins/superpowers-whetstone/skills/red-synthesize-green .cursor/skills/red-synthesize-green && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "red-synthesize-green" agent skill from https://github.com/SebastienDegodez/copilot-instructions/tree/main/plugins/superpowers-whetstone/skills/red-synthesize-green into .cursor/skills/red-synthesize-green/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "red-synthesize-green", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/SebastienDegodez/copilot-instructions.git --path plugins/superpowers-whetstone/skills/red-synthesize-green--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install SebastienDegodez/copilot-instructions red-synthesize-green --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/SebastienDegodez/copilot-instructions.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/plugins/superpowers-whetstone/skills/red-synthesize-green .gemini/skills/red-synthesize-green && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "red-synthesize-green" agent skill from https://github.com/SebastienDegodez/copilot-instructions/tree/main/plugins/superpowers-whetstone/skills/red-synthesize-green into .gemini/skills/red-synthesize-green/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "red-synthesize-green", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install SebastienDegodez/copilot-instructions red-synthesize-greenInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/SebastienDegodez/copilot-instructions.git skills-src && mkdir -p .github/skills && cp -r skills-src/plugins/superpowers-whetstone/skills/red-synthesize-green .github/skills/red-synthesize-green && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "red-synthesize-green" agent skill from https://github.com/SebastienDegodez/copilot-instructions/tree/main/plugins/superpowers-whetstone/skills/red-synthesize-green into .github/skills/red-synthesize-green/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "red-synthesize-green", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install SebastienDegodez/copilot-instructions red-synthesize-green --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/SebastienDegodez/copilot-instructions.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/plugins/superpowers-whetstone/skills/red-synthesize-green .opencode/skills/red-synthesize-green && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "red-synthesize-green" agent skill from https://github.com/SebastienDegodez/copilot-instructions/tree/main/plugins/superpowers-whetstone/skills/red-synthesize-green into .opencode/skills/red-synthesize-green/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "red-synthesize-green", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
red-synthesize-green- GitHub stars
- 198
- Token cost
- ~1.4k tokens
- SKILL.md length
- 697 words
- Files
- 1
- Skills in repo
- 19
- Repo updated
- First seen
- Licence
- Apache-2.0
At a glance
A skill your agent uses when implementing any feature or fix using TDD, before writing any implementation code
- Works in 2 steps: RED (Behavior Failure Only) → SYNTHESIZE GREEN (Clean Synthesis)
- Implementing any feature
- SKILL.md covers Overview, Step 1: RED (Behavior Failure…, Between Steps: Architectural… and Step 2: SYNTHESIZE GREEN…, plus 6 more sections
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
What it does
Red Synthesize Green is an agent skill from SebastienDegodez/copilot-instructions. Use when implementing any feature or fix using TDD, before writing any implementation code
Its SKILL.md is about 1.4k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.
It sits in Testing & QA, covering Test-driven development. The repository describes itself as: A comprehensive codebase of best practices, coding rules, and workflow automation for AI-assisted development with GitHub Copilot. Includes DDD, Clean Architecture, testing… The licence is Apache-2.0.
When your agent uses it
- Implementing any feature
- Before writing any implementation code
Example prompts
- “/red-synthesize-green”
Workflow steps
2 steps, taken from the step headings in SKILL.md.
What it can do on your machine
Read from SKILL.md and the folder at commit 0f0dccf. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Red Synthesize Green loads about 1.4k tokens when it runs. Until then it costs about 28 tokens; SKILL.md has 697 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from SebastienDegodez/copilot-instructions at commit 0f0dccf, republished under its Apache-2.0 licence (© SebastienDegodez). 697 words, ~1,373 tokens.
Download SKILL.mdSave it as
.claude/skills/red-synthesize-green/SKILL.md (or your agent's skills folder).- name
- red-synthesize-green
- description
- Use when implementing any feature or fix using TDD, before writing any implementation code
RED → SYNTHESIZE GREEN (AI TDD Cycle)
Overview
2-step cycle replacing traditional 3-step TDD. Optimized for AI synthesis.
- Traditional (3 steps): RED → green (dirty) → Refactor
- AI-Optimized (2 steps): RED (behavior failure) → SYNTHESIZE GREEN (clean synthesis)
Architectural guidance is mandatory between steps.
Hard rule: No implementation code before RED is a clean behavior failure.
Step 1: RED (Behavior Failure Only)
Write the failing test. Run it.
- Compilation errors = wishful thinking phase → implement stubs/empty returns to compile, rerun
- Assertion/behavior failure = RED ✓ → proceed to Step 2
- Never treat compilation errors as RED
Programming by Wishful Thinking: When your test won't compile, you're discovering the API you need. Stub just enough to compile, then confirm the test fails on behavior.
Between Steps: Architectural Guidance (MANDATORY)
Hard rule: This step is not skippable. Do not proceed to SYNTHESIZE GREEN without completing it.
Developer must review and explicitly validate the test before continuing. AI pauses here and waits for developer confirmation that the test correctly captures the intended behavior.
Orient design before synthesis:
- Which pattern? (specification, factory, builder)
- Which layer owns the logic?
- Immutability, return values vs mutations?
Step 2: SYNTHESIZE GREEN (Clean Synthesis)
Implement complete, clean, production-ready solution in one shot.
- Follows all architectural rules and coding standards
- No dirty-then-refactor — synthesize properly from the start
- Idiomatic code, domain semantics, SOLID principles
- If test was misunderstood → revise test, restart from RED
No iteration after SYNTHESIZE GREEN unless RED was wrong or architectural guidance changed.
Common Rationalizations
| Excuse | Reality |
|---|---|
| "Compilation error IS red" | No. Compilation = wishful thinking. RED = behavior failure. |
| "I'll write dirty code then refactor" | That's 3-step TDD. SYNTHESIZE GREEN produces clean code. |
| "I can skip RED, I know it'll fail" | Run it. RED proves your test catches real failures. |
Red Flags — STOP and Restart
- Implementation code before RED is a behavior failure
- Compilation errors treated as RED
- Skipping RED entirely
- Skipping the Between Steps architectural guidance
- Proceeding to SYNTHESIZE GREEN without developer test validation
- Refining code after SYNTHESIZE GREEN instead of revising RED
Any of these mean: Delete code, start over with proper RED.
Quick Reference
| Phase | What | Success Criteria |
|---|---|---|
| RED | Write test, stub until compiles, run | Test fails on behavior (assertion), not compilation |
| Guidance (MANDATORY) | Orient architectural approach + developer validates test | Design direction clear, developer has confirmed test |
| SYNTHESIZE GREEN | Synthesize complete clean solution | Tests green, architecture respected, production-ready |
Show full SKILL.md (313 more words)Show less
When Orchestrating Subagents (MANDATORY)
If you are an orchestrating agent using subagent-driven-development:
NEVER put RED and SYNTHESIZE GREEN in the same subagent prompt.
Split every TDD task into two separate dispatches:
- Dispatch 1 — RED only: subagent writes test, stubs to compile, runs to confirm behavior failure, reports the failing test output
- YOU pause — show the failing test to the developer, wait for explicit confirmation ("ok, proceed")
- Dispatch 2 — SYNTHESIZE GREEN: only after developer approves the test
The mandatory human validation checkpoint is the orchestrator's responsibility. It cannot be delegated to the subagent.
Red flags — you are violating this rule if:
- Your subagent prompt contains both "write the failing test" AND "implement the solution"
- You wrote
PAUSEin a plan comment but included all steps in one prompt - You assumed the developer would confirm via the plan document
| Rationalization | Reality |
|---|---|
| "The pause is in the plan text" | Plans are documentation. Dispatch boundaries are enforcement. |
| "The subagent will stop and ask" | Subagents execute what they receive. Split the prompt. |
| "It's more efficient in one shot" | Efficiency that skips developer validation is not efficiency. |
Integration
REQUIRED BACKGROUND: superpowers-whetstone:outside-in-tdd — defines the two test streams (Application + Domain) that this cycle drives.
Quality Gate Ownership
This skill owns the strict TDD quality gate for business logic layers:
- Application and Domain logic must reach 100% code coverage before completion.
- Mutation testing on Application and Domain logic must end with 0 non-equivalent surviving mutants.
- Any equivalent mutant must be explicitly documented with justification.
If one of these conditions is not met, work is not complete.
Behavior-first workflow: When used with superpowers-whetstone:outside-in-tdd:
superpowers-whetstone:gherkin-gatedefines WHAT (observable behavior)- Acceptance tests map scenarios to executable tests (RED phase)
- This skill enforces the RED → validation → SYNTHESIZE GREEN cycle
superpowers-whetstone:mutation-testingvalidates test quality after GREEN (before merge)
Pair with domain-specific testing skills for patterns and examples.
© SebastienDegodez, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
Just SKILL.md in plugins/superpowers-whetstone/skills/red-synthesize-green of SebastienDegodez/copilot-instructions.
Open the folder on GitHubat commit 0f0dccf
Compare with similar skills
Red Synthesize Green next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Red Synthesize Green this skillSebastienDegodez/copilot-instructions | 198 | — | ~1.4k | Automated safety check: Pass | Apache-2.0 | |
| TDDpietheinstrengholt/rssmonster | 564 | 30 repos | ~906 | Automated safety check: Pass | MIT | |
| TDD WorkflowhellangleZ/burn-in-cceverywhere-ralph | 112 | 11 repos | ~2.4k | Automated safety check: Pass | None | |
| TDDsanity-io/sanity | 6.4k | 20 repos | ~1k | Automated safety check: Pass | MIT | |
| Test Driven Developmentfarm-fe/farm | 5.6k | 52 repos | ~2.5k | Automated safety check: Pass | MIT | |
| Tapd Story PipelineTencentBlueKing/bk-bcs | 840 | — | ~2.6k | Automated safety check: Pass | Custom licence |
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Related
Categories
Questions about Red Synthesize Green
What does Red Synthesize Green do?
A skill your agent uses when implementing any feature or fix using TDD, before writing any implementation code. Red Synthesize Green is an agent skill from SebastienDegodez/copilot-instructions.
When should I use Red Synthesize Green?
Red Synthesize Green fits situations like: implementing any feature; before writing any implementation code.
How do I install Red Synthesize Green in Claude Code?
Run `npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a claude-code`. Or copy the skill folder (plugins/superpowers-whetstone/skills/red-synthesize-green in SebastienDegodez/copilot-instructions) into .claude/skills/red-synthesize-green in your project. Claude Code loads it when a task matches its description.
How do I install Red Synthesize Green in Codex?
Run `npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a codex`. Or copy the skill folder (plugins/superpowers-whetstone/skills/red-synthesize-green in SebastienDegodez/copilot-instructions) into .agents/skills/red-synthesize-green in your project. Codex loads it when a task matches its description.
Can I use Red Synthesize Green in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add SebastienDegodez/copilot-instructions --skill red-synthesize-green -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/red-synthesize-green, .gemini/skills/red-synthesize-green, .github/skills/red-synthesize-green and .opencode/skills/red-synthesize-green in your project.
What does Red Synthesize Green need to run?
SKILL.md names no scripts, command-line tools or credentials: Red Synthesize Green is instructions for the agent only.
Does Red Synthesize Green access the network?
SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.
Is Red Synthesize Green safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Red Synthesize Green use?
Red Synthesize Green is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Red Synthesize Green use?
About 1.4k tokens (SKILL.md is roughly 5.5k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to Red Synthesize Green?
Skills that share tags, products or a category with Red Synthesize Green: TDD (pietheinstrengholt/rssmonster, 564 stars), TDD Workflow (hellangleZ/burn-in-cceverywhere-ralph, 112 stars), TDD (sanity-io/sanity, 6.4k stars) and Test Driven Development (farm-fe/farm, 5.6k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Red Synthesize Green?
SebastienDegodez (a GitHub user) maintains it in SebastienDegodez/copilot-instructions, which has 198 GitHub stars. The repository holds 19 skills in this directory. The repository was last updated on October 6, 2026.
Source: SebastienDegodez/copilot-instructions on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.