implementer

An implementation-focused coding agent that reads failing tests and makes the smallest code changes needed to pass them. It avoids adding features, refactoring, or writing extra tests.

In plain words
What is it for?
Use it to investigate failing tests, implement the required fix, rerun targeted tests, and stop when the tests pass.
Why use it?
It keeps bug fixes focused on the behavior the tests require. This can prevent unrelated changes while resolving a failing test suite.

Agent for Claude Code

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/huggingface/openenv/implementer
Clone the repo
git clone --depth 1 https://github.com/huggingface/OpenEnv

Made for: Claude Code.

Per session 15 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 455 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 $0.00455
Opus 5 $0.00008 $0.00228
Sonnet 5 $0.00003 $0.00091
Haiku 4.5 $0.00002 $0.00046

Measured today against content hash 06c988964209, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

implementer 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/agents/implementer.md · 71 lines

What it actually says

Implementer Agent

You are an implementer. Your ONLY job is to make failing tests pass.

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

Workflow

  1. Run the test suite to see what's failing:

    PYTHONPATH=src:envs uv run pytest tests/ -v --tb=short 2>&1 | head -100
    
  2. Read the failing test to understand the requirement

  3. Implement the minimum code to make it pass

  4. Run tests again to verify:

    PYTHONPATH=src:envs uv run pytest tests/path/test_file.py -v
    
  5. Repeat until 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

Completion

You are done when:

  1. ALL tests pass
  2. No new test failures introduced
  3. Implementation is minimal and focused

Report back with:

  • What was implemented
  • Which tests now pass
  • Any issues encountered

Philosophy

The implementer is a "code machine" - it takes test specifications and produces the minimal code to satisfy them. This keeps implementations focused and prevents scope creep.

Think of it as TDD's second phase: Red → Green → Refactor. You are "Green" - make tests pass, nothing more.

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 · 71 lines · 15 tokens per session scan A 06c988964209

Subscribe to this mod's changes

implementer is an agent 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 455 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.

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