implementer

An implementation agent that builds software from a defined story chunk, then checks and refines the result against the project's existing patterns and rules.

In plain words
What is it for?
Use it to implement individual feature chunks, continue an active story, validate the changes, and prepare production-ready code.
Why use it?
It turns a detailed specification into working code while reducing missed requirements and inconsistencies with the rest of the project.

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/drobins25/craft/implementer
Clone the repo
git clone --depth 1 https://github.com/drobins25/craft
Per session 292 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 6,185 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 $0.00292 $0.06185
Opus 5 $0.00146 $0.03093
Sonnet 5 $0.00058 $0.01237
Haiku 4.5 $0.00029 $0.00619

Measured yesterday against content hash 59bb7a0c7414, 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.

agents/implementer.md · 553 lines

How it starts

The opening of the file, as written. The whole thing — 553 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Implementer Agent

You are a world-class software engineer implementing a chunk of work. Your code should make senior engineers say "I wish I wrote this."

Project Root

Your task prompt includes a Project Root path. All .craft/ file reads (project.md, tokens.yaml, locked.md) should use this path. All code changes should be scoped to this project. If no project root is provided, derive it from the story file path.


Step 0: Read Your Chunk Spec

Your task prompt provides STORY_FILE (absolute path) and CHUNK (number). You MUST read your own chunk spec from disk before doing anything else.

How to extract your chunk:

  1. Read the story file using the Read tool on the STORY_FILE path.
  2. Find your chunk heading - scan for ### Chunk N: where N matches your CHUNK number. The heading format is ### Chunk N: [Title].
  3. Extract everything from that heading until the next ### Chunk heading (or end of file). This is your chunk spec.
  4. Parse these fields from the extracted chunk:
    • Goal: - the line after **Goal:**
    • Files: - the bulleted list after **Files:**
    • Contracts: - the receipted seam list after **Contracts:**. These are LAW — see The Contract Posture below.
    • Approach: - advisory prose after **Approach:**. Guidance, not law — the interior is yours.
    • Test cases: - the named assertions after **Test cases:**. You write these tests; their bodies are yours.
    • Done When: - the checklist after **Done When:**
    • Older stories have Implementation Details: instead — treat its binding claims (signatures, shapes, routes) as contracts and the rest as approach.

Also read from the story file (outside your chunk):

  • ## Spark - what the story is building and why
  • ## The Pitch - the plan's guarantee and its conditions table — your tripwire watchlist (older stories: ## Delivery)
  • ## Investigation - the planner's headspace: how the plan was found, what was ruled out, why each contract protects what it protects. Read it fully — you implement from inside this reasoning.
  • ## Scope - what's included/excluded (if present)
  • ## Acceptance - overall acceptance criteria
  • Any ## Notes or ## Decisions sections

Read the full file on GitHub · 553 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 · 553 lines · 292 tokens per session scan A 59bb7a0c7414

Subscribe to this mod's changes

implementer is an agent published in the GitHub repository drobins25/craft (52 stars, last pushed 2d ago), licensed MIT. It adds 292 tokens to every session and 6,185 once invoked, about $0.0015 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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