feature-implement-loop

A feature-building workflow that takes a description and acceptance criteria, writes code and tests, reviews the result for gaps, and repeats the work when needed.

In plain words
What is it for?
Use it to implement a feature or user story, test its required behavior, and look for edge cases, security issues, and missed acceptance criteria.
Why use it?
It checks whether the implementation actually meets the stated definition of done instead of stopping after code generation.

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/sananthanarayan/skilldrop/feature-implement-loop
Any agent
npx skills add sananthanarayan/skilldrop --skill feature-implement-loop
Clone the repo
git clone --depth 1 https://github.com/sananthanarayan/skilldrop

Made for: Claude Code, Codex.

Per session 111 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,264 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 $0.00111 $0.02264
Opus 5 $0.00056 $0.01132
Sonnet 5 $0.00022 $0.00453
Haiku 4.5 $0.00011 $0.00226

Measured yesterday against content hash 3913d5144795, 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-loop 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.

skills/feature-implement-loop/SKILL.md · 89 lines

How it starts

The opening of the file, as written. The whole thing — 89 lines — stays where its author put it; the contents beside it link to each section on GitHub.

feature-implement-loop

You drive a feature from spec to verified implementation through a self-correcting loop. The differentiator over plain code generation: you don't stop at "here's the code." You implement, adversarially challenge what you wrote, and regenerate to close the gaps — until every acceptance criterion has a passing test and the review surfaces no blocker/major findings, or a hard 3-round cap stops you and you report what's still open.

This is the dev-workflow loop counterpart to the artifact pipeline. It composes the devils-advocate review philosophy — driven as a full reviewer panel (correctness, security, craft) where subagents exist — into a build cycle. At the human's invocation layer it stands alone: hand it a spec, get back checked code.

Input

A feature/story with two parts:

  • Description — what to build and why.
  • Acceptance criteria — the conditions that define "done." If the user gives prose without explicit criteria, extract the implicit criteria first and echo them back as a numbered list before writing any code. No criteria, no loop — the criteria are the gate.

If acceptance criteria are missing and can't be inferred, ask for them (one question). Don't invent a gate the user didn't agree to.

How to respond

  1. Restate the spec as a criteria checklist. Number every acceptance criterion. This list is the contract the loop closes against — each criterion must end the run mapped to a test.

  2. Plan the verification first. For each criterion, name the test that will prove it (unit / integration / e2e, and the assertion). Surface criteria that can't be tested automatically (e.g. "looks good on mobile") and flag them as manual-verify up front — they don't block the loop but must appear in the final report.

  3. Generate code + tests together. Write the implementation and the tests that cover the criteria in the same pass. Follow the repo's existing conventions, language, and test framework — read a neighbouring file first; don't impose a new style.

Read the full file on GitHub · 89 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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 · 89 lines · 111 tokens per session scan A 3913d5144795

Subscribe to this mod's changes

feature-implement-loop is a skill published in the GitHub repository sananthanarayan/skilldrop (2 stars, last pushed 18d ago), licensed MIT. It adds 111 tokens to every session and 2,264 once invoked, about $0.0006 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.

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