write-minimal-implementation

A TDD step that writes only the code needed to make a failing test pass. TDD, or test-driven development, means writing a test first and then implementing the behavior it checks.

In plain words
What is it for?
Use it after a test fails or code does not compile. It identifies the missing behavior, adds the smallest implementation, and runs the specific test to check the result.
Why use it?
It prevents untested features, premature optimization, and extra code from being added before they are needed.

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/djscheuf/agentic-dev-ecosystem-template/write-minimal-implementation
Any agent
npx skills add djscheuf/agentic-dev-ecosystem-template --skill write-minimal-implementation
Clone the repo
git clone --depth 1 https://github.com/djscheuf/agentic-dev-ecosystem-template

Made for: Claude Code, Codex.

Per session 41 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 966 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 $0.00041 $0.00966
Opus 5 $0.00020 $0.00483
Sonnet 5 $0.00008 $0.00193
Haiku 4.5 $0.00004 $0.00097

Measured 2d ago against content hash cfa080dca801, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

write-minimal-implementation 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 2d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (verify.sh), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

.devin/skills/write-minimal-implementation/SKILL.md · 142 lines

How it starts

The opening of the file, as written. The whole thing — 142 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Workflow Steps

Step 1: Analyze the Failure

Review the test failure:
- What class/method is missing?
- What behavior is not implemented?
- What's the simplest fix?

Step 2: Write Minimal Implementation

CRITICAL: Write ONLY enough code to pass the test.

Acceptable approaches:
- Return a hardcoded value
- Implement the simplest algorithm
- Add the minimal structure needed

FORBIDDEN:
- Implementing features not tested
- Adding error handling not tested
- Optimizing prematurely
- Adding "obvious" code paths

Step 3: Make It Compile

If the test fails due to missing types/methods:

1. Create the class/interface if missing
2. Add method signatures with minimal body
3. Return default/hardcoded values initially

Example progression:
// Step 1: Make it compile
public class Calculator
{
    public int Add(int a, int b) => 0; // Just compile
}

// Step 2: Make it pass
public class Calculator
{
    public int Add(int a, int b) => 5; // Hardcoded for first test
}

Step 4: Run the Test

Execute ONLY the specific test:
- dotnet test --filter "TestName"
- pytest -k "test_name"
- npm test -- --grep "test name"

Verify:
✓ The specific test now passes
✓ No compilation errors
✓ Test passes for the right reason

// TODO - Add Run-Test Skill specific to the project's testing framework, supporting that projects structure.

Step 5: Run All Tests

Ensure no regressions:
- Run the entire test suite
- All tests should pass
- If any test fails, fix immediately

If new failures appear:
- Your change broke something
- Revert and reconsider approach
- Smaller steps needed

// TODO - Add Run-Test Skill specific to the project's testing framework, supporting that projects structure, and specifically declares how to run all of a projects/subprojects tests.

Step 6: Document the Success

Update the test plan and mark that test as "passing".

Step 7: Write the Sentinel File

  • create a sentinel file in the .process directory, named {skill-name}.done.json.
  • the sentinel file will follow @/schema/sentinel.schema.json.
  • set the task field to "{skill-name}".
  • the verify_params of the sentinel file will follow @/schema/verify-params.schema.json.
  • set the verify_params as follows:
    • set "test_cases_path" to the path of the test cases file relative to repo root.
    • set "failing_test_path" to the path of the failing test file relative to repo root.
    • set "failing_test_name" to the name of the failing test.
    • set "changed_code_files" to an array of paths to all the changed code files relative to repo root.

Read the full file on GitHub · 142 lines

Files

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.

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. 2d ago First seen · 142 lines · 41 tokens per session scan A cfa080dca801

Subscribe to this mod's changes

write-minimal-implementation is a skill published in the GitHub repository djscheuf/agentic-dev-ecosystem-template (12 stars, last pushed 2d ago), licensed MIT. It adds 41 tokens to every session and 966 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 2026-08-30.

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