What is api-contract-sync?

A tool for keeping the agreed shape of an API—the interface one program uses to communicate with another—consistent between frontend and backend services. It detects differences, creates client SDKs, and handles API versions.

Detecting API contract drift, generating client libraries, and organizing changes between API versions.

Frontend and backend code can stop matching as they change independently. Keeping the contract aligned helps prevent integration failures.

api-contract-sync — Skill for Claude Code by fanlw0816/harness-creator

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.

Any agent

npx skills add fanlw0816/harness-creator --skill api-contract-sync

Clone the repo

git clone --depth 1 https://github.com/fanlw0816/harness-creator

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/fanlw0816/harness-creator/api-contract-sync/github.svg)](https://agentmods.dev/skills/fanlw0816/harness-creator/api-contract-sync)

Your own site

<a href="https://agentmods.dev/skills/fanlw0816/harness-creator/api-contract-sync"><img src="https://agentmods.dev/badge/skills/fanlw0816/harness-creator/api-contract-sync/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/fanlw0816/harness-creator/api-contract-sync"><img src="https://agentmods.dev/badge/skills/fanlw0816/harness-creator/api-contract-sync.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 31 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,337 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.

Origin unknown 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	$0.00031	$0.02337
Opus 5.5	$0.00012	$0.00935
Sonnet 5.5	$0.00006	$0.00467
Haiku 4.5	$0.00003	$0.00234

Measured 2mo ago against content hash 30ebb801d6fb, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

api-contract-sync 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.

references/base/multi-project/skills/api-contract-sync/SKILL.md · 385 lines

The source is not reproduced here

No licence file

Read it on GitHub

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 · 385 lines · 31 tokens per session scan A 30ebb801d6fb

Subscribe to this mod's changes

api-contract-sync is a skill published in the GitHub repository fanlw0816/harness-creator (11 stars, last pushed 7mo ago), with no licence file. It adds 31 tokens to every session and 2,337 once invoked, about $0.0001 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.

Backend and APIs Frontend

api-contract-sync next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
api-contract-syncfanlw0816/harness-creator	Skill	11	7mo ago	none	A	31	Claude Code
mem0-oss-to-platformmem0ai/mem0	Skill	69k	yesterday	Apache-2.0	A	217	Claude Code, Codex
azure-mgmt-botservice-dotnetmicrosoft/skills	Skill	3.2k	yesterday	MIT	A	78	Claude Code
fastapi-router-pymicrosoft/skills	Skill	3.2k	yesterday	MIT	A	46	Claude Code
dev-runtimelangwatch/langwatch	Skill	5.0k	today	Apache-2.0	A	172	Claude Code
api-designericrisco/rsc-harness	Skill	529	3d ago	MIT	A	105	Claude Code, Codex
migrate-segw-to-raparc-mcp/arc-1	Skill	253	today	MIT	A	106	Claude Code