spec-driven-implementation

A workflow for implementing a code change from a written product or technical specification, design document, issue plan, or acceptance criteria. It turns the stated requirements into a plan, code changes, and checks.

In plain words
What is it for?
Use it to implement a feature or fix, update relevant tests, compare the result with each requirement, and report verification and risks.
Why use it?
It reduces the risk of missing requirements or adding unrequested work. It also makes conflicts, compatibility concerns, and skipped checks visible.

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/pymodel/pythinker-cli/spec-driven-implementation
Any agent
npx skills add PyModel/pythinker-cli --skill spec-driven-implementation
Clone the repo
git clone --depth 1 https://github.com/PyModel/pythinker-cli

Made for: Claude Code, Codex.

Per session 25 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 233 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 $0.00025 $0.00233
Opus 5 $0.00013 $0.00117
Sonnet 5 $0.00005 $0.00047
Haiku 4.5 $0.00003 $0.00023

Measured yesterday against content hash 33cb2ba6c056, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

spec-driven-implementation 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.

src/pythinker_code/skills/spec-driven-implementation/SKILL.md · 39 lines

What it actually says

Spec-Driven Implementation

Use when the task references a product spec, tech spec, design doc, issue plan, or explicit acceptance criteria.

Workflow

  1. Read the relevant spec files or acceptance criteria.
  2. Extract required behavior, non-goals, constraints, and verification gates.
  3. Map the existing implementation and tests before editing.
  4. Produce a short implementation plan tied to the spec.
  5. Make surgical changes only for the requested behavior.
  6. Check the implementation against each requirement.
  7. Run the smallest meaningful verification gate and report any skipped gate.

Rules

  • Do not implement unstated nice-to-haves.
  • If the spec conflicts with existing code or another spec, stop and surface the conflict.
  • Preserve public compatibility unless the spec explicitly changes it.
  • Add or update tests when behavior changes and the project has relevant tests.

Output

Return:

SUMMARY
SPEC REQUIREMENTS
CHANGES
SPEC CHECK
VERIFICATION
RISKS
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 · 39 lines · 25 tokens per session scan A 33cb2ba6c056

Subscribe to this mod's changes

spec-driven-implementation is a skill published in the GitHub repository PyModel/pythinker-cli (20 stars, last pushed 4d ago), licensed Apache-2.0. It adds 25 tokens to every session and 233 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 2026-08-30.

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