spec-implement

A workflow for carrying out an approved software design and implementation plan. It uses test-driven development, or TDD, meaning tests are written and used to guide the code, and reports progress between groups of tasks.

In plain words
What is it for?
Use it to persist missing design or plan files, implement planned changes with TDD, track tasks, and report progress.
Why use it?
It prevents implementation from starting before required design and planning documents exist. It also keeps execution tied to the approved plan and stops when work is blocked.

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/martinffx/atelier/spec-implement
Any agent
npx skills add martinffx/atelier --skill spec-implement
Clone the repo
git clone --depth 1 https://github.com/martinffx/atelier

Made for: Claude Code, Codex.

Per session 63 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,157 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 $0.00063 $0.02157
Opus 5 $0.00032 $0.01078
Sonnet 5 $0.00013 $0.00431
Haiku 4.5 $0.00006 $0.00216

Measured 2d ago against content hash 7ed8e3cd3c16, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

spec-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 2d ago.

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.

skills/spec-implement/SKILL.md · 298 lines

How it starts

The opening of the file, as written. The whole thing — 298 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Spec Implement

Execute the approved Spec-backed Plan. Track progress when it uses tracked tasks. Report. Stop when blocked.

Announce at start: "I'm using the spec-implement skill to execute this plan."

This skill does not make design decisions or change approved content. It may persist approved content from the conversation when Plan Mode could not write the required artifact. If the plan is wrong, go back to spec-plan. If the design is wrong, go back to spec-brainstorm.

Prerequisites

Resolve required artifacts in order before starting product implementation:

  1. If docs/specs/YYYY-MM-DD-<feature>/design.md is missing, write it from the approved design in the current conversation. Validate the file, report its path, and stop. Do not create plan.json or start implementation in the same invocation.
  2. Otherwise, if docs/specs/YYYY-MM-DD-<feature>/plan.json is missing, write it from the approved plan in the current conversation. Validate it against the schema in spec-plan, report its path, and stop. Do not start implementation in the same invocation.
  3. If the approved content needed for the next missing artifact is not available in the current conversation, stop and tell the human what content is unavailable. Do not ask the human to create the file.
  4. When both artifacts exist, verify that any tracker entries selected during planning are available, along with docs/agents/issue-tracker.md when tracking is configured.
  5. Verify that you are not on main/master without explicit user consent. Create a branch or use a git worktree first.

Each invocation creates at most one missing artifact. Only proceed to product implementation when both approved artifacts existed at the start of the invocation.


Step 1: Load and Review the Plan

Read plan.json critically before writing code. Look for:

  • Unclear or ambiguous tasks
  • Missing file paths or incomplete validation criteria
  • Tasks that conflict with each other
  • Dependencies that don't match what you see in the codebase
  • Existing code or platform behavior that already satisfies a planned capability
  • Duplicate IDs, parsers, errors, schemas, lifecycle handling, or test utilities
  • Shared abstractions with fewer than two current consumers
  • Tests whose only purpose is validating a new wrapper

Read the full file on GitHub · 298 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. 2d ago First seen · 298 lines · 63 tokens per session scan A 7ed8e3cd3c16

Subscribe to this mod's changes

spec-implement is a skill published in the GitHub repository martinffx/atelier (44 stars, last pushed 23d ago), licensed MIT. It adds 63 tokens to every session and 2,157 once invoked, about $0.0003 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.