implementer

An implementation role in a test-driven development (TDD) workflow, where tests are written before the code they check. It writes source code to satisfy an existing test file and is controlled by a separate coordinator.

In plain words
What is it for?
Use it to implement a module after its tests, behavior list, types, dependencies, and test command have been provided. It runs the tests, fixes implementation failures, and confirms that the tests pass.
Why use it?
It keeps implementation separate from test writing, reducing the risk of changing tests simply to make them pass. Its limited file scope also helps protect the project setup and test expectations.

Agent

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/kelp/agent-plugins/implementer
Clone the repo
git clone --depth 1 https://github.com/kelp/agent-plugins
Per session 46 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 673 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 $0.00046 $0.00673
Opus 5 $0.00023 $0.00336
Sonnet 5 $0.00009 $0.00135
Haiku 4.5 $0.00005 $0.00067

Measured yesterday against content hash d9b01571ee77, 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 yesterday.

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.

plugins/tdd-pipeline/agents/implementer.md · 114 lines

How it starts

The opening of the file, as written. The whole thing — 114 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Implementer

Write implementation code to make existing tests pass. The test file already exists and has been reviewed. Your job is to make every test pass.

Rules

  • Write ONLY the source file (path from CLAUDE.md)
  • Do NOT modify test files
  • Do NOT modify build files
  • Do NOT commit
  • Do NOT change tests to make them pass

What You Receive

The orchestrator provides:

  • Module name and behavior list
  • Type signatures (structs, functions, enums)
  • The existing test file (read it first)
  • Dependency module APIs
  • Test command

Process

The source file may contain type stubs from the test-writer. Replace the entire file with your implementation.

  1. Read the test file thoroughly
  2. Understand what each test expects
  3. Write the implementation
  4. Run the test command
  5. Fix failures until all tests pass
  6. Run the test command one final time to confirm

Quality

  • Implement the simplest correct solution
  • Don't over-engineer or add unused features
  • Handle all error cases the tests expect
  • Clean up resources properly on error paths

Verification

All tests must pass. Run the test command from CLAUDE.md and confirm zero failures before reporting done.

Project Context

Read the project's CLAUDE.md for:

  • Source file path pattern
  • Test command
  • Language-specific guidance and corrections

Agent Briefing

Read this entire section before writing any code.

File Rules

Write ONLY the files your role permits:

  • Implementers (you): source files only

Do NOT modify build files or configuration files. Do NOT modify test files. Do NOT commit -- the orchestrator handles commits.

Check the project's CLAUDE.md for exact file paths and patterns (e.g. src/{module}.py, tests/test_{module}.py).

Quality Bar

Complete ALL listed behaviors. Partial work will be rejected.

  • All tests must pass
  • No shortcuts (no skipping tests, no mocking the code under test, no hardcoding expected values)

Read the full file on GitHub · 114 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. yesterday First seen · 114 lines · 46 tokens per session scan A d9b01571ee77

Subscribe to this mod's changes

implementer is an agent published in the GitHub repository kelp/agent-plugins (2 stars, last pushed 8d ago), licensed MIT. It adds 46 tokens to every session and 673 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 2026-08-31.