What is cairn-loop-implement?

An implementation-and-test procedure handles one unit of work in a Cairn development loop. Cairn is a workflow that breaks larger changes into isolated units with defined success checks.

Use it during the Implement step to create or adopt the unit branch, make the smallest qualifying code change, update the blueprint when needed, and add its test.

It keeps each unit on the required branch, limits the change to what the success criterion needs, and requires a test for changed behavior. This makes the unit ready for a separate verification step.

How cairn-framework/cairn configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to cairn-framework/cairn. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/cairn-framework/cairn/main/.claude/skills/cairn-loop-implement/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/cairn-framework/cairn

Made for: Claude Code.

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/cairn-framework/cairn/cairn-loop-implement/github.svg)](https://agentmods.dev/skills/cairn-framework/cairn/cairn-loop-implement)

Your own site

<a href="https://agentmods.dev/skills/cairn-framework/cairn/cairn-loop-implement"><img src="https://agentmods.dev/badge/skills/cairn-framework/cairn/cairn-loop-implement/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/cairn-framework/cairn/cairn-loop-implement"><img src="https://agentmods.dev/badge/skills/cairn-framework/cairn/cairn-loop-implement.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 65 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 778 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

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.

Model	Per session	Once invoked
Fable 5.1	$0.00065	$0.00778
Opus 5.5	$0.00026	$0.00311
Sonnet 5.5	$0.00013	$0.00156
Haiku 4.5	$0.00006	$0.00078

Measured 2mo ago against content hash 494752565288, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

cairn-loop-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 2mo 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.

.claude/skills/cairn-loop-implement/SKILL.md · 77 lines

How it starts

The opening of the file, as written. The whole thing — 77 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Implement one loop unit

Loaded by cairn-dev loop mode at its Implement and test step. Inputs: the selected unit, its resolved node, the success criterion from cairn-loop-scope, and the bound $CAIRN.

Declared exits, exactly one, as the last line you return to loop mode:

IMPLEMENTED: the change is written and its test exists; loop mode runs Verify.
LOOP HALTED: implementation cannot proceed without a maintainer.

1. Get on the right branch

The branch is loop/<tail>, where <tail> is the derived form from loop mode's Isolation rule: todo.<slug>, <finding-code>.<node>, or split.<slug>. Every later step (push, PR, Cleanup) uses this exact name.

If it is already checked out (adopted at verdict time, or created earlier this session during MISSION materialisation or decomposition), continue on it. Otherwise create it from fresh origin/main:

git checkout --detach origin/main && git checkout -b loop/<tail>

If the derived name already exists but was NOT adopted by the verdict and NOT created this session, you missed a preflight row. Do not improvise and do not halt here: return to loop mode's preflight table, which owns that state and can adopt or quarantine the branch. Say which name collided.

2. Make the smallest change that satisfies the criterion

Not the best change you can think of. The smallest one that makes the criterion true. Anything else is a separate unit.

Touch only what the criterion requires. Do not improve adjacent code, reformat, or refactor things that are not broken. Match the surrounding style even where you would have chosen differently.
Remove imports, variables, and helpers that YOUR change orphaned. Leave pre-existing dead code alone; mention it instead.
If you write far more code than the criterion needs, stop and reconsider. A senior engineer calling the result overcomplicated is a defect.

3. Keep the blueprint honest

The graph must still describe the code when you are done:

Every new file falls under a node path, tests included. If none fits, extend a node's paths or declare a new Module.
Every new cross-module call gets a blueprint edge. Check for a cycle first: $CAIRN deps <target> --transitive.
User-facing strings go to the copy location named by loop mode's Repo bindings. Never hardcode them in source, and never guess the path: read the binding.

Read the full file on GitHub · 77 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.

2mo ago First seen · 77 lines · 65 tokens per session scan A 494752565288

Subscribe to this mod's changes

cairn-loop-implement is a skill published in the GitHub repository cairn-framework/cairn (53 stars, last pushed yesterday), licensed Apache-2.0. It adds 65 tokens to every session and 778 once invoked, about $0.0003 per session on Opus 5.5. 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.

E2E testing Planning TDD Testing

cairn-loop-implement next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
cairn-loop-implementcairn-framework/cairn	Skill	53	yesterday	Apache-2.0	A	65	Claude Code
nw-test-design-mandatesnWave-ai/nWave	Skill	631	yesterday	MIT	A	69	Claude Code
nw-bdd-methodologynWave-ai/nWave	Skill	631	yesterday	MIT	A	52	Claude Code
nw-test-organization-conventionsnWave-ai/nWave	Skill	631	yesterday	MIT	A	33	Claude Code
testingnotque/vexjoy-agent	Skill	446	3d ago	MIT	A	23	Claude Code
nw-ad-critique-dimensionsnWave-ai/nWave	Skill	631	yesterday	MIT	A	53	Claude Code
nw-spikenWave-ai/nWave	Skill	631	yesterday	MIT	A	32	Claude Code

cairn: Skill for Claude Code