feature-implement-execute

feature-implement-execute is a command for coding agents from axiomantic/spellbook. It costs 22 tokens per session (11,056 once invoked), scanned A, original, MIT.

A command for carrying out an approved software implementation plan. It applies each task with TDD—writing or updating tests as part of development—and checks the work before completion.

In plain words
What is it for?
Use it to implement planned features, run tests and quality checks for each task, review changes, and confirm the finished result.
Why use it?
It prevents coding from starting without an agreed plan and keeps each task subject to testing and review. This helps catch changes that appear complete but do not meet the intended behavior.

Command

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 commands/axiomantic/spellbook/feature-implement-execute
Clone the repo
git clone --depth 1 https://github.com/axiomantic/spellbook

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for feature-implement-execute

README.md
[![agentmods](https://agentmods.dev/badge/commands/axiomantic/spellbook/feature-implement-execute.svg)](https://agentmods.dev/commands/axiomantic/spellbook/feature-implement-execute)
Your own site
<a href="https://agentmods.dev/commands/axiomantic/spellbook/feature-implement-execute"><img src="https://agentmods.dev/badge/commands/axiomantic/spellbook/feature-implement-execute.svg" alt="Measured on agentmods" height="20"></a>
Per session 22 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 11,056 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 $0.00022 $0.11056
Opus 5 $0.00011 $0.05528
Sonnet 5 $0.00004 $0.02211
Haiku 4.5 $0.00002 $0.01106

Measured yesterday against content hash da6dc053e2ac, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

feature-implement-execute 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.

commands/feature-implement-execute.md · 1,200 lines

How it starts

The opening of the file, as written. The whole thing — 1,200 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Implementation Execution (/feature-implement-execute)

Phase 4 of the develop workflow. Run after /feature-implement completes (Phase 3 planning approved; for large delegated runs, the 3.4.7 one-pager approved).

Do NOT begin Phase 4 until the "STOP AND VERIFY: Phase 3 → Phase 4 Transition" checklist at the end of /feature-implement passes IN FULL. If ANY item is unchecked: STOP and return to /feature-implement.

On the zero-flag fast path, the user-confirmed inline plan (<=5 steps) stands in for the Phase 3 artifacts; every other Phase 4 gate below still runs.

Anti-rationalization: "the plan is small" / "the gates are overkill here" = Pattern 3 (Time Pressure) or Pattern 5 (Competence Assertion). The review floor is never zero.

Invariant Principles

  1. Design precedes implementation - Never implement without an approved design document and implementation plan
  2. Delegate actual work - Main context orchestrates; subagents write code, run tests, perform reviews
  3. Quality gates are mandatory - Code review, fact-checking, and green mirage audit after every task; no exceptions
  4. Behavior preservation in refactoring - Test verification at every transformation; no behavior changes without approval
  5. No batch exemption - A batched or multi-task dispatch exempts NOTHING: every task the batch covers passes the per-task gates 4.4, 4.5, and 4.5.1 individually before it may be marked complete. Batch size never substitutes for per-task gating.

Read the full file on GitHub · 1,200 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 · 1,200 lines · 22 tokens per session scan A da6dc053e2ac

Subscribe to this mod's changes

feature-implement-execute is a command published in the GitHub repository axiomantic/spellbook (10 stars, last pushed yesterday), licensed MIT. It adds 22 tokens to every session and 11,056 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 2026-09-03.