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 vaquarkhan/Fullstack-development-agent-skills --skill api-contract-first-developmentgit clone --depth 1 https://github.com/vaquarkhan/Fullstack-development-agent-skillsWrote 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/vaquarkhan/fullstack-development-agent-skills/api-contract-first-development)<a href="https://agentmods.dev/skills/vaquarkhan/fullstack-development-agent-skills/api-contract-first-development"><img src="https://agentmods.dev/badge/skills/vaquarkhan/fullstack-development-agent-skills/api-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/vaquarkhan/fullstack-development-agent-skills/api-contract-first-development"><img src="https://agentmods.dev/badge/skills/vaquarkhan/fullstack-development-agent-skills/api-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 | $0.00039 | $0.00436 |
| Opus 5.5 | $0.00016 | $0.00174 |
| Sonnet 5.5 | $0.00008 | $0.00087 |
| Haiku 4.5 | $0.00004 | $0.00044 |
Grade A, and why
api-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.
How it starts
The opening of the file, as written. The whole thing — 58 lines — stays where its author put it; the contents beside it link to each section on GitHub.
API Contract-First Development
Use When
- Designing or changing REST, GraphQL, or event contracts between UI and services
- Backward compatibility or versioning decisions are required
Workflow
- Capture consumer needs and edge cases.
- Draft contract schema and examples.
- Define versioning and compatibility guarantees.
- Implement provider and consumer validation.
- Release with deprecation timeline when needed.
Required Checks
- Include required and optional fields explicitly
- Define error envelope and status mapping
- Publish examples for happy and failure paths
- Avoid breaking changes without a migration path
- Contract tests run in CI
- Existing consumers remain compatible
- Deprecations are documented and announced
Decision Framework
- Draft OpenAPI, GraphQL, or event schema before provider or consumer code merges.
- Classify every field change as safe additive, breaking, or deprecated-with-timeline.
- Consumer-driven contract tests must run in CI for every published schema revision.
- Version endpoints or use compatibility headers when multiple consumer generations coexist.
Common Rationalizations And Rebuttals
- "We can document the API after shipping." -> Undocumented contracts drift; consumers embed assumptions that break silently.
- "Breaking changes are fine if we own all clients." -> Mobile, partner, and async consumers lag deploys; assume external consumers exist.
- "Examples in code comments are enough." -> CI cannot validate comments; publish machine-readable schemas and examples.
Evidence Pack
- Published schema artifact with diff against previous version
- Consumer contract test results (provider and consumer suites)
- Deprecation timeline and migration guide for breaking changes
- Error envelope examples for validation, auth, and not-found paths
Exit Criteria
- Workflow decisions are documented and implementation-ready
- Validation evidence exists for quality, reliability, and compatibility
- Operational readiness and rollback expectations are explicit
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 · 58 lines · 39 tokens per session scan A 27d51768c5af
api-contract-first-development is a skill published in the GitHub repository vaquarkhan/Fullstack-development-agent-skills (3 stars, last pushed 1mo ago), licensed MIT. It adds 39 tokens to every session and 436 once invoked, about $0.0002 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 2026-09-07.
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