implement

A test-driven coding helper that implements the smallest code changes needed to make existing failing tests pass.

In plain words
What is it for?
Use it after a test-writing step has created failing tests. It reads those tests, changes the relevant code, reruns the tests, and stops when all pass.
Why use it?
It removes the guesswork from turning tests into working code and checks the result after each change. It is meant for requirements already expressed as failing tests, not untested features or refactoring.

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/huggingface/openenv/implement
Any agent
npx skills add huggingface/OpenEnv --skill implement
Clone the repo
git clone --depth 1 https://github.com/huggingface/OpenEnv

Made for: Claude Code, Codex.

Per session 15 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 623 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 $0.00015 $0.00623
Opus 5 $0.00008 $0.00311
Sonnet 5 $0.00003 $0.00125
Haiku 4.5 $0.00002 $0.00062

Measured today against content hash 825d870b8fd3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

implement 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 today.

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.

.claude/skills/implement/SKILL.md · 101 lines

How it starts

The opening of the file, as written. The whole thing — 101 lines — stays where its author put it; the contents beside it link to each section on GitHub.

/implement

Make failing tests pass with minimal code.

Usage

/implement

The implementer will automatically find failing tests from the most recent /write-tests run.

When to Use

  • After /write-tests has created failing tests
  • When you have specific tests that need implementation
  • Never before tests exist

When NOT to Use

  • No failing tests exist (run /write-tests first)
  • You want to add features not covered by tests
  • You want to refactor (use /simplify instead)

What It Does

  1. Finds the failing tests from /write-tests
  2. Reads tests to understand requirements
  3. Writes the minimum code to make tests pass
  4. Runs tests after each change
  5. Stops when ALL tests pass

Output

The implementer agent will produce:

## Implementation Complete

### Tests Passed
- `test_client_reset_returns_observation` ✓
- `test_client_step_advances_state` ✓
- `test_client_handles_invalid_action` ✓

### Changes Made
| File | Change |
|------|--------|
| `src/openenv/core/client.py` | Added `reset()` method |
| `src/openenv/core/client.py` | Added `step()` method |
| `src/openenv/core/client.py` | Added input validation |

### Verification

PYTHONPATH=src:envs uv run pytest tests/test_client.py -v All 3 tests passed


### Next Steps
- Mark todo as complete
- Consider `/simplify` if change was large
- Move to next pending todo

Rules

  1. Read the failing tests first to understand exactly what's needed
  2. Write the MINIMUM code needed to pass tests
  3. Run tests after each change to verify progress
  4. Do NOT add extra features not covered by tests
  5. Do NOT refactor existing code (that's /simplify's job)
  6. Stop when all tests pass

Anti-patterns (NEVER do these)

  • Adding features not covered by tests
  • Refactoring existing code
  • Writing additional tests (that's /write-tests's job)
  • Over-engineering solutions
  • Adding comments or documentation beyond what's necessary
  • "Improving" code that already works

Read the full file on GitHub · 101 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. today First seen · 101 lines · 15 tokens per session scan A 825d870b8fd3

Subscribe to this mod's changes

implement is a skill published in the GitHub repository huggingface/OpenEnv (2,531 stars, last pushed 3d ago), licensed BSD-3-Clause. It adds 15 tokens to every session and 623 once invoked, about $0.0001 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.

Related

Other skills, from other repositories

systematic-debugging

Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes.

obra/superpowers · 21 tokens

next-cache-components-adoption

Turn on Cache Components in a Next.js app and resolve the blocking routes it surfaces. Use when the user wants to enable, adopt, or migrate to Cache Components, flip the cacheComponents flag, work through a flood of blocking-prerender / instant validation errors, run the cache-components-instant-false codemod, or…

vercel/next.js · 95 tokens

babysit-pr

Babysit a GitHub pull request after creation by continuously polling review comments, CI checks/workflow runs, and mergeability state until the PR is merged/closed or user help is required. Diagnose failures, retry likely flaky failures up to 3 times, auto-fix/push branch-related issues when appropriate, and keep…

openai/codex · 114 tokens

imagegen

Generate or edit raster images when the task benefits from AI-created bitmap visuals such as photos, illustrations, textures, sprites, mockups, or transparent-background cutouts. Use when Codex should create a brand-new image, transform an existing image, or derive visual variants from references, and the output…

openai/codex · 113 tokens

cpu-profile-analysis

Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating…

microsoft/vscode · 71 tokens

next-cache-components-optimizer

Drive a Next.js route to instant navigation by setting up an agentic loop, under Cache Components / PPR, on initial load (hard navigation) and client-side navigation (soft navigation). Encode the goal as a failing @next/playwright instant() e2e and work it to green, one verified route at a time; the shipped test then…

vercel/next.js · 170 tokens