The Complete Production SOP: How to Deploy and Run OpenAPI 3.1 & REST Contract Validator in Autonomous AI Agents
Step-by-step SOP to install and run OpenAPI-Craft in Codex, Claude Code, and Cursor. Author OpenAPI 3.1 specs, generate TS SDKs, and mock responses safely.
Technical Overview & Architectural Context
Autonomous coding agents frequently stumble when authoring API contracts. Standard LLMs hallucinate OpenAPI 3.0 syntax within OpenAPI 3.1 manifests—confusing JSON Schema 2020-12 dialect support with legacy OpenAPI constructs such as `nullable: true` instead of `type: ['string', 'null']`. Furthermore, agents frequently produce syntactically valid YAML specifications that silently fail downlevel TypeScript SDK generator passes (such as openapi-typescript or openapi-fetch) or trigger runtime schema mismatches during Prism mock testing. The `openapi-craft` skill establishes strict deterministic boundaries for agents operating inside Codex, Claude Code, Cursor, and Windsurf. By enforcing a 4-stage validation workflow—schema authoring under JSON Schema 2020-12 semantics, structural AST linting with Spectral, automated TypeScript type compilation, and Prism mock contract verification—this skill prevents hallucinated endpoints, broken polymorphism (`oneOf`/`anyOf`), and misaligned payload signatures before PR submission.
Prerequisites & Environment Requirements
Verified Search Intents & Long-Tail Queries Solved
This operational tutorial is engineered to provide deterministic solutions for these developer search queries:
Step-by-Step Execution Playbook
Local Environment Setup & SKILL.md Mounting
Mount openapi-craft into your agent's runtime skills registry and project repository.
Agent runtimes such as Claude Code, Codex, Cursor, and Windsurf discover deterministic procedures via the `.agents/skills` or `.claude/skills` directory tree. Mounting this file gives the agent explicit procedural constraints, forcing it to inspect existing `openapi.yaml` or `openapi.json` schemas before generating endpoints, SDK code, or mock fixtures.
mkdir -p .agents/skills/openapi-craft && curl -fsSL https://askills.dev/api/skills/openapi-craft/raw -o .agents/skills/openapi-craft/SKILL.md---
name: "openapi-craft"
description: "Author OpenAPI 3.1 schemas, generate TypeScript client SDKs, and mock HTTP responses."
runtimes: ["codex", "claude-code", "cursor", "windsurf"]
---
# OpenAPI 3.1 & REST Contract Validator Rules
1. Always specify `openapi: 3.1.0` in the document root.
2. In OpenAPI 3.1, never use `nullable: true`. Instead, use JSON Schema type arrays: `type: ["string", "null"]`.
3. Validate every spec change against `@stoplight/spectral-cli` with the `spectral:oas` ruleset.
4. Ensure every operationId is unique, camelCased, and mirrors the intent (e.g., `listOrganizations`, `createUserWorkspace`).
5. Generate client SDK interfaces with `openapi-typescript` immediately after spec updates.Keep the SKILL.md under 150 lines to prevent unneeded token overhead in Claude Code and Codex context windows; offload heavy lint rule definitions to a local `.spectral.yaml` file.
Ensure the agent has read access to the root directory where `SKILL.md` resides. In containerized Cursor or Codex sandboxes, non-whitelisted paths outside the repo root will silently fail to load.
Tooling and Validation Dependency Verification
Install and verify schema linting, mocking, and type-generation packages in the sandbox.
To allow the agent to execute self-correction loops autonomously, install Stoplight Spectral, Prism CLI, and openapi-typescript as local devDependencies. The agent uses CLI exit codes to diagnose contract errors without human prompting.
pnpm add -D @stoplight/spectral-cli @stoplight/prism-cli openapi-typescript typescriptextends: ["spectral:oas"]
rules:
operation-operationId-valid-in-url: off
oas3-api-servers: error
oas3-schema: error
typed-enum: errorInject an npm script `"lint:api": "spectral lint ./specs/**/*.yaml"` into `package.json` so the agent can run short, standard verification routines.
Prism CLI may attempt to bind to `0.0.0.0:4010`. In restricted CI/sandbox runtimes, instruct the agent to run Prism against `127.0.0.1` to prevent permission violations.
Intent Matching & Trigger Invocation
Invoke the agent using contract-centric terminology that deterministically triggers openapi-craft.
LLM agent engines scan user prompts against the skill frontmatter description. Using target phrases like 'OpenAPI 3.1 contract', 'Spectral linting', or 'generate openapi-typescript SDK' ensures immediate skill activation over generic text edits.
Structure prompts using the 'Context -> Contract -> Target Output' formula for highest accuracy across Claude Code and Codex.
Do not request partial YAML snippets in prompts without asking the agent to validate the whole document; otherwise, unclosed schema refs like `$ref: '#/components/schemas/User'` will break compilation.
Verification, Linting & Output Quality Gate
Execute the 3-step quality gate: Spectral schema linting, type emission, and mock verification.
The final stage of openapi-craft requires the agent to run the validation chain, verify exit code 0, compile emitted TypeScript interfaces, and spin up an ephemeral Prism instance to ensure endpoints return valid mocks.
pnpm exec spectral lint docs/specs/openapi.yaml && pnpm exec openapi-typescript docs/specs/openapi.yaml -o src/api/v1-schema.d.ts && pnpm exec tsc --noEmitReview `git diff docs/specs/openapi.yaml` before confirming the commit to ensure the agent did not unintentionally strip description or summary fields.
If `openapi-typescript` emits `never` types for request bodies, verify that your OpenAPI 3.1 specification has properly declared the `content: application/json` mapping under `requestBody`.
Real-World Scenario: Authoring a Paginated Billing Events API in OpenAPI 3.1 with TypeScript SDK
“Add a new paginated endpoint `/v1/billing/events` to our OpenAPI 3.1 specification. The endpoint must support cursor-based pagination, return an ISO-8601 timestamp, allow null values for `metadata`, validate with Spectral, and regenerate the typed SDK.”
Runtime Troubleshooting & Failure Modes
Root Cause: The agent authored the field using OpenAPI 3.0 conventions (`nullable: true`) instead of OpenAPI 3.1 standard JSON Schema 2020-12 multi-type declarations.
Sed or prompt command: Replace `type: string\nnullable: true` with `type: ["string", "null"]` in `docs/specs/openapi.yaml` and re-run Spectral.Root Cause: The agent referenced a shared error component that was not declared in the root `components.schemas` block, breaking OpenAPI reference resolution.
pnpm exec spectral lint --verbose-rules docs/specs/openapi.yaml && echo 'Ensure components.schemas.ErrorResponse is defined in the components block.'Frequently Asked Questions (OpenAPI 3.1 & REST Contract Validator SOP)
Q:Can I use OpenAPI 3.1 & REST Contract Validator across Codex, Claude Code, and Cursor simultaneously?
Yes. The skill conforms to the universal SKILL.md specification. Placing it in your repository's `.agents/skills/openapi-craft/` directory makes it automatically accessible to Codex, Claude Code, Cursor, and Windsurf without runtime modification.
Q:How does OpenAPI 3.1 & REST Contract Validator prevent context window overflow during long agent sessions?
By establishing a deterministic CLI validation loop. Instead of the agent dumping entire 5,000-line OpenAPI schemas into chat memory, it executes external CLI commands (Spectral and openapi-typescript) and only processes granular exit code errors, saving thousands of LLM context tokens.
Q:Does this skill require escalated root or container permissions?
No. It is audited with a security score of 98/100 and strictly operates within workspace-scoped file paths using local development tools. It requires no elevated host privileges or remote network tunnels.
Ready to equip your autonomous agent with OpenAPI 3.1 & REST Contract Validator?
Copy the complete audited SKILL.md specification or download the 1-click zip bundle directly from our verified registry.