API Documentation Project — Complete Guide

In this tutorial, you will learn about API Documentation Project. We cover key concepts, practical examples, and best practices to help you master this topic.

Apply everything you have learned by building a complete API documentation set from scratch including an OpenAPI 3.1 spec, interactive reference documentation, getting started guide, authentication docs, error catalog, changelog with breaking change notes, and SDK quickstart for your API.

What You'll Learn

How to plan and execute a complete API documentation project, how to create all documentation components that support each other, how to validate your documentation with automated tools, and how to publish your documentation to a developer portal.

Why It Matters

Creating a complete API documentation set from scratch demonstrates mastery of all the skills from this course. Employers and clients want to see that you can deliver a complete developer experience, not just endpoint descriptions in isolation.

Real-World Use

The DodaTech developer portal was built from scratch by following the same Process outlined in this project. The team started with the OpenAPI spec, generated reference docs, wrote guides, and set up CI validation. The portal now serves thousands of developers monthly.

Project Components

flowchart TD
  A[API Documentation Project] --> B[Planning]
  A --> C[OpenAPI Spec]
  A --> D[Reference Docs]
  A --> E[Getting Started]
  A --> F[Auth Docs]
  A --> G[Error Catalog]
  A --> H[Changelog]
  A --> I[SDK Quickstart]
  A --> J[CI Pipeline]
  B --> K[Choose API]
  B --> L[Define scope]
  C --> M[5+ endpoints]
  C --> N[3+ schemas]
  A:::current
  classDef current fill:#f90,color:#fff,stroke:#333,stroke-width:2px

Project Requirements

Your complete API documentation project must include:

1. OpenAPI 3.1 spec — At least 5 endpoints across 2 resource groups, 3 reusable schemas, authentication scheme, error responses, and tags
2. Interactive reference docs — Generated from the spec using Redoc or Swagger UI
3. Getting started guide — Zero-to-working-code in under 5 minutes
4. Authentication documentation — How to get and use credentials
5. Error code catalog — At least 10 error codes with causes and solutions
6. Changelog — At least 3 version entries with one breaking change
7. SDK quickstart — How to use the API from one SDK with code examples
8. CI pipeline — Validates spec and generates docs automatically

Step-by-Step Plan

Step 1: Choose Your API

Select an API you know well. Options include:

• A personal project or side project API
• A fictional API you design from scratch
• An existing open-source API you want to document
• A company API you work with

Step 2: Write the OpenAPI Spec

openapi: 3.1.0
info:
  title: My API
  version: 1.0.0
  description: API documentation project
servers:
  - url: https://api.example.com/v1
paths:
  /items:
    get:
      summary: List items
      tags: [Items]
      parameters:
        - name: page
          in: query
          schema:
            type: integer
      responses:
        "200":
          description: List of items
components:
  schemas:
    Item:
      type: object
      properties:
        id:
          type: string
        name:
          type: string
  securitySchemes:
    BearerAuth:
      type: http
      scheme: bearer

Step 3: Generate Reference Docs

npx @redocly/cli build-docs openapi.yaml -o docs/reference.html

Step 4: Write the Getting Started Guide

# Getting Started

## Prerequisites
- API key from https://dashboard.example.com

## First Request
```bash
curl -H "Authorization: Bearer YOUR_KEY" https://api.example.com/v1/items

### Step 5: Create Error Catalog

```markdown
| Status | Code | Cause | Solution |
|--------|------|-------|----------|
| 401 | UNAUTHORIZED | Missing or invalid API key | Generate a new key |
| 404 | NOT_FOUND | Resource does not exist | Check the resource ID |

Step 6: Write Changelog

## v1.1.0 (2026-07-01)
- Added pagination to list endpoints
- Fixed sorting by date

## v1.0.0 (2026-06-28)
- Initial release

Step 7: Set Up CI

name: Docs CI
on: [push]
jobs:
  validate:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npx @stoplight/spectral lint openapi.yaml
      - run: npx @redocly/cli build-docs openapi.yaml -o public/

Common Mistakes

1. Scope Too Large

Attempting to document a 50-endpoint API with multiple auth methods for the first project. Focus on 5-8 endpoints and one authentication method.

2. No Spec Validation

Writing the OpenAPI spec without validating it leads to syntax errors. Always run Spectral before generating docs.

3. Broken Code Examples

Publishing examples that have not been tested against the real API. Test every example before releasing.

4. Missing Interactive Docs

Generating only static markdown without an interactive playground. Developers need try-it-out functionality.

5. No CI Pipeline

Manual documentation updates are skipped when deadlines loom. Set up automated generation and deployment from day one.

6. No Error Documentation

Documenting only success responses. Error documentation is essential for production integrations.

7. Forgetting Mobile

Writing docs that assume desktop browsers. Ensure the documentation portal works on mobile devices.

Practice Questions

1. What are the 8 components of a complete API documentation project?

OpenAPI spec, interactive reference docs, getting started guide, authentication docs, error code catalog, changelog with breaking changes, SDK quickstart, and CI pipeline.

2. Why start with a small scope for the API documentation project?

A focused project with 5 well-documented endpoints is more valuable than 20 poorly documented endpoints. Small scope ensures each component is complete and high quality.

3. What is the most critical validation step?

OpenAPI spec validation with Spectral. An invalid spec breaks all generated docs and tools. Validate before generating anything.

4. How do you know if the documentation project is successful?

A developer who has never seen your API should be able to make a successful API call in under 5 minutes using only your documentation.

5. Challenge: Complete all 8 components of the API documentation project. Deploy the documentation to a public URL. Write a Retrospective on what you would improve next time.

FAQ

Mini Project: Complete Developer Portal

Build and deploy a complete API developer portal. Include all 8 components from this lesson. Deploy to a public URL. Test the portal with a developer who has not seen your API. Measure their time to first successful API call. Document the results and suggested improvements.

What's Next

Congratulations on completing the Writing API Documentation course! Apply these skills to API Documentation for a deeper dive into OpenAPI specs and tools. Or explore Technical Writing for more documentation topics.