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.
npx skills add niels-emmer/myace --skill contract-first-developmentgit clone --depth 1 https://github.com/niels-emmer/myaceWrote 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.
[](https://agentmods.dev/skills/niels-emmer/myace/contract-first-development)<a href="https://agentmods.dev/skills/niels-emmer/myace/contract-first-development"><img src="https://agentmods.dev/badge/skills/niels-emmer/myace/contract-first-development/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.
<a href="https://agentmods.dev/skills/niels-emmer/myace/contract-first-development"><img src="https://agentmods.dev/badge/skills/niels-emmer/myace/contract-first-development.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00021 | $0.00290 |
| Opus 5.5 | $0.00008 | $0.00116 |
| Sonnet 5.5 | $0.00004 | $0.00058 |
| Haiku 4.5 | $0.00002 | $0.00029 |
Grade A, and why
Contract-First Development 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 1mo 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.
What it actually says
Purpose
Prevent frontend-backend integration bugs by defining the contract before building either side.
When to use it
Starting a new feature that touches both frontend and backend.
Checklist
- Define the contract first: OpenAPI spec as the source of truth for request/response shapes, error codes, auth requirements, pagination.
- Codegen: use openapi-typescript, orval, or equivalent to generate client types from the spec.
- Shared types package: if not using codegen, maintain a shared package with types both sides import.
- Contract tests: use consumer-driven contracts (Pact) or request/response snapshot tests to catch drift.
- Breaking change protocol: deprecate fields before removing them; never silently rename or change types.
- Document the contract location: every contributor knows where to find the canonical spec.
Expected output
A documented API contract that both frontend and backend implement against, with automated checks preventing drift.
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.
- 1mo ago First seen · 29 lines · 21 tokens per session scan A 5fb49e6ccf10
Contract-First Development is a skill published in the GitHub repository niels-emmer/myace (1 stars, last pushed 2d ago), licensed MIT. It adds 21 tokens to every session and 290 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 2026-09-03.
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