# How I read an OpenAPI file before using an API

A beginner-friendly guide to OpenAPI and Swagger documents, paths, methods, parameters, request bodies, responses, and using an OpenAPI Viewer.

- Date: 2026-09-27
- URL: https://ilham.dev/posts/how-to-read-an-openapi-file-before-using-an-api/
- Markdown: https://ilham.dev/posts/how-to-read-an-openapi-file-before-using-an-api/index.md
- Tags: openapi, swagger, api, tools
- Reading time: 2 min


An OpenAPI file is machine-readable API documentation. It describes endpoints, inputs, outputs, and authentication expectations.

The [OpenAPI Viewer](/tools/openapi-viewer/) tool gives me a safe place to test the idea before I put it into a script, server, or production workflow.

## The simple mental model

An OpenAPI file is machine-readable API documentation. It describes endpoints, inputs, outputs, and authentication expectations.

I try to reduce the tool to one question: what input do I have, what output do I expect, and what would make the result unsafe or misleading?

## Step 1: Open the OpenAPI or Swagger document

Open the OpenAPI or Swagger document.

Start with a small example first. A small example is easier to inspect than a real production-sized case.

## Step 2: Scan the list of paths

Scan the list of paths.

## Step 3: Choose one operation

Choose one operation.

## Step 4: Read required parameters

Read required parameters.

## Step 5: Inspect the request body schema

Inspect the request body schema.

## Step 6: Read possible responses

Read possible responses.

## Step 7: Check authentication requirements before writing code

Check authentication requirements before writing code.

## My checklist

Before I trust the result, I check:

- Open the OpenAPI or Swagger document.
- Scan the list of paths.
- Choose one operation.
- Read required parameters.
- Inspect the request body schema.
- Read possible responses.
- Check authentication requirements before writing code.

The tool saves time, but the important part is still understanding the input and reviewing the output before using it somewhere important.