🔎 OpenAPI/Swagger Viewer
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Parse OpenAPI 3.x (YAML/JSON) and Swagger 2.0 specs into an interactive collapsible tree. Color-coded HTTP method badges, Expand All / Collapse All controls, and zero server round-trips — built on 43KB js-yaml only.
Parse OpenAPI 3.x (YAML or JSON) or Swagger 2.0 specs instantly into an interactive collapsible tree. Color-coded HTTP method badges (GET=blue, POST=green, PUT=orange, DELETE=red, PATCH=purple, HEAD/OPTIONS/TRACE=neutral) make API structure scannable at a glance. Expand and collapse paths, operations, parameters, responses, and schemas with native browser controls. Built on js-yaml (43KB) — no server round-trips, unlike Swagger UI (1.5MB) or Redoc (800KB+). Your spec never leaves your browser. 1 MB input cap with clear error messages.
Supports OpenAPI 3.0 / 3.1 (YAML, JSON) and Swagger 2.0. All parsing runs in your browser.
📋 When to Use the OpenAPI/Swagger Viewer
You have an OpenAPI or Swagger spec and need to understand its structure fast — without spinning up Swagger UI (1.5 MB) or Redoc (800 KB+). Paste the YAML or JSON here and get an interactive, color-coded tree in milliseconds. Perfect for reviewing PR changes, debugging API contracts, or exploring third-party APIs offline. Everything runs in your browser; your spec (which may contain internal paths, example values, or auth schemes) never leaves your device.
⚙️ How the OpenAPI/Swagger Viewer Works
The viewer uses js-yaml (43 KB) to parse YAML into a JavaScript object; JSON is parsed natively. It detects the spec version from the openapi field (3.x) or swagger field (2.0). Then it walks the paths object, rendering each path with its HTTP methods as color-coded badges. Operations expand to show summary, parameters (with location, type), responses (status codes + descriptions), and request body schemas. All rendering is pure DOM — <details> / <summary> for native collapse/expand, no framework overhead. Input is capped at 1 MB to protect browser memory; larger specs show a clear error. Output is escaped to prevent XSS from malicious spec content.
How to Use the OpenAPI/Swagger Viewer
- Paste your spec — Drop OpenAPI 3.x (YAML or JSON) or Swagger 2.0 into the input. A sample OpenAPI 3.0 YAML is pre-loaded on first visit.
- Click Parse Spec — The spec is validated and rendered as a collapsible tree with color-coded HTTP method badges.
- Explore the tree — Click paths to expand operations, parameters, responses, and schemas. Use Expand All / Collapse All for quick navigation.
- Your data stays local — No network requests. The spec never leaves your browser.
Frequently Asked Questions
Which OpenAPI/Swagger versions are supported?
OpenAPI 3.0, 3.1 (YAML and JSON) and Swagger 2.0. The viewer detects the version from the openapi or swagger field.
What is the maximum spec size?
1 MB. Larger specs are rejected with a clear error message to protect browser memory. Most real-world specs are well under this limit.
Does this tool send my spec to a server?
No. All parsing and rendering runs entirely in your browser using js-yaml. Your API spec never leaves your device.
Can I view specs with external $ref references?
External references (to other files/URLs) cannot be resolved in a standalone browser tool. The viewer shows $ref values as-is but cannot fetch external files. For specs with external refs, bundle them first (e.g., with swagger-cli bundle or @redocly/openapi-cli bundle).
Why are some method badges a different color?
Standard HTTP methods (GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS, TRACE) have distinct colors. Non-standard or custom methods fall back to a neutral badge without special coloring.
How is this different from Swagger UI or Redoc?
Swagger UI (~1.5 MB) and Redoc (~800 KB+) are full-featured documentation generators with servers, OAuth flows, and try-it-out panels. This viewer is a lightweight (~43 KB js-yaml) tree renderer for quick structural review — no server, no auth, no try-it-out, zero dependencies beyond js-yaml.
Cite this tool
@misc{toolstand_openapiviewer,
title = {OpenAPI/Swagger Viewer},
author = {{ToolStand}},
year = {2026},
url = {https://toolstand.io/tools/openapi-viewer/}
}Using this tool in a post or paper? Copy a ready-made reference above.