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Skill Guide

API and integration specification - documenting LLM API contracts, rate limits, latency expectations, and error handling

The formal practice of creating precise, machine-readable and human-readable documentation that defines an LLM service's endpoints, input/output schemas, usage constraints (rate limits), performance guarantees (latency SLAs), and error response protocols.

This skill is critical because it directly reduces integration friction, enables reliable automation, and mitigates operational risk. A well-specified API contract is the foundation for scalable and maintainable system architecture, directly impacting developer velocity and system uptime.
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8.7 Avg Demand
20% Avg AI Risk

How to Learn API and integration specification - documenting LLM API contracts, rate limits, latency expectations, and error handling

1. Master OpenAPI Specification (OAS) 3.0 fundamentals: define paths, operations, schemas, and security. 2. Understand core concepts of rate limiting (token bucket, sliding window) and latency percentiles (p50, p95, p99). 3. Study standard HTTP error codes (4xx, 5xx) and design consistent, structured error response bodies (e.g., including error codes, messages, and request IDs).
1. Move from documentation to specification-as-code: generate server stubs and client SDKs from OpenAPI specs using tools like Swagger Codegen or OpenAPI Generator. 2. Implement and document a tiered rate-limiting strategy (e.g., per-user, per-API-key, per-endpoint) using API gateways. 3. Define and document explicit SLAs for latency under different load conditions and model sizes, moving beyond averages to percentile-based guarantees.
1. Architect and govern a specification-first development workflow across multiple engineering teams, ensuring versioning and backward compatibility. 2. Design sophisticated, context-aware error handling and retry strategies that account for transient LLM failures (e.g., 503s, 429s with Retry-After headers). 3. Integrate specification validation into CI/CD pipelines and use contract testing tools (e.g., Pact) to prevent integration drift between services.

Practice Projects

Beginner
Project

Document a Simple LLM Chat Completion Endpoint

Scenario

You are tasked with documenting a new `/v1/chat/completions` endpoint for a fictional LLM provider. The endpoint accepts a message history and returns an assistant's response.

How to Execute
1. Create an OpenAPI 3.0 YAML file defining the POST operation, request body schema (with `messages` array, `model` string, `max_tokens` integer), and response schema. 2. Document a sample rate limit of 60 requests per minute per API key in the spec description. 3. Define error responses for invalid requests (400), unauthorized access (401), and server errors (500) with standardized JSON error bodies. 4. Use Swagger UI or Redoc to render the documentation.
Intermediate
Project

Build a Tiered Rate-Limiting and Latency-SLA API Gateway

Scenario

You need to protect a backend LLM service and provide clear usage contracts. Different customer tiers (Free, Pro, Enterprise) have different rate limits and latency expectations.

How to Execute
1. Use an API gateway (e.g., Kong, AWS API Gateway) to implement rate limiting. Define tiers: Free (10 req/min), Pro (100 req/min), Enterprise (1000 req/min). 2. Write middleware to add `X-RateLimit-Limit`, `X-RateLimit-Remaining`, and `X-RateLimit-Reset` headers to every response. 3. Document the p95 latency SLA for each tier (e.g., Free: 2000ms, Pro: 1000ms, Enterprise: 500ms) in the API specification. 4. Implement a `Retry-After` header on 429 responses. 5. Set up monitoring to track actual latency percentiles vs. SLA.
Advanced
Project

Establish a Specification-as-Code Pipeline for a Microservices Fleet

Scenario

Your organization has multiple internal services consuming a central LLM API. Integration failures due to contract drift are causing outages. You must implement a robust specification governance model.

How to Execute
1. Design a Git repository structure where the OpenAPI spec is the source of truth. 2. Set up a CI pipeline that uses a linter (e.g., Spectral) to enforce style rules and validates the spec on every PR. 3. Use OpenAPI Generator to auto-generate TypeScript and Python client SDKs, published as internal packages. 4. Implement consumer-driven contract testing using Pact. A consumer service writes a contract defining its expectations of the provider (LLM API). The provider's CI runs these pact tests to ensure it meets all consumer expectations. 5. Integrate the published SDKs and contract test results into the developer portal and deployment gates.

Tools & Frameworks

Specification & Documentation

OpenAPI Specification (OAS)Swagger Editor / RedocStoplight Studio

OpenAPI is the industry standard for defining RESTful APIs. Swagger/Redoc render interactive docs from the spec. Stoplight Studio provides a GUI for designing and mocking APIs.

API Management & Gateways

KongAWS API GatewayAzure API ManagementApigee

These platforms enforce rate limiting, authentication, logging, and latency monitoring at the gateway layer. They are essential for implementing the operational aspects of the contract.

Testing & Validation

Spectral (Linting)Pact (Contract Testing)Postman (Collection Testing)OpenAPI Generator

Spectral enforces spec style and quality. Pact verifies provider-consumer contracts. Postman tests live endpoints. OpenAPI Generator creates client/server code from the spec.

Monitoring & Observability

Prometheus / GrafanaDatadogCloudWatch

Used to track and alert on real-time metrics for rate limit consumption and latency percentiles (p50, p95, p99) against the documented SLAs.

Careers That Require API and integration specification - documenting LLM API contracts, rate limits, latency expectations, and error handling

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