The archive · Developer & Business Tools · Product decision · 2023–2026
OpenAPI DevTools bets specs should come from traffic, not docs; 811-point Show HN
Andrew Walsh's Chrome/Firefox extension turns live network requests into OpenAPI 3.1 specs; the 2023-10-25 Show HN drew 811 points, 4.3k GitHub stars
OpenAPI DevTools (Andrew Walsh)
What the business is
OpenAPI DevTools is a browser extension that adds an OpenAPI tab to browser DevTools and generates OpenAPI 3.1 specifications in real time from the network requests a site actually makes — automatically merging headers, bodies and query parameters per endpoint, recognizing path parameters, previewing the spec with Redoc, and letting users export, import or share sessions.
How it started
Andrew Walsh built the extension around the gap between standards and reality: OpenAPI is the modern standard for REST APIs, governed by the OpenAPI Initiative and the Linux Foundation, and systems that have specs are far easier to work with — yet discovering a site's API behaviour usually means depending on docs that may not exist. The tool records what actually happens: it converts the JSON requests that fire while a developer browses into a specification, and where an endpoint responds inconsistently (a value sometimes a string and sometimes null), the spec records both until more data arrives.
What happened
The material shows the project expanding across surfaces: the repo's 'Important' note announces that a new and final version was rewritten from scratch, with automatic path-parameter identification, a desktop app using a proxy (e.g. mitm2swagger), a website and CLI that generate OpenAPI specifications from HAR files (e.g. har-to-openapi), a published library for middleware, DevOps integrations or any environment, curl and client-code generation plus an auto-populating API client, and the ability to translate into different OpenAPI versions or reverse-engineer other HTTP standards such as GraphQL. The extension itself shipped in the Chrome Web Store and Firefox Add-on Store.
How it ended up
As of the 2026-09-04 crawl the original repository is live at 4.3k stars and 86 forks, with the README pointing development at Demystify, a from-scratch successor whose repository describes a desktop proxy app, browser extension, CLI and library. No company, funding or revenue is documented in the material.
Background
OpenAPI DevTools is a browser extension by Andrew Walsh that adds an OpenAPI tab to Chrome and Firefox DevTools and converts the network requests an app really makes into an OpenAPI 3.1 specification in real time. Headers, bodies and query parameters are merged automatically per endpoint, path parameters are recognized from repeated requests, the spec previews inside the tool with Redoc, and sessions can be exported, imported or shared.
The bet is that API documentation should be generated from observed traffic instead of hand-written: the README's pitch is 'effortlessly discover API behaviour' for any app or website, and the tool is deliberately additive — every matching future request to an endpoint merges into the spec, and values that vary (string or null) are recorded as both until more evidence arrives.
Attention was immediate: the Show HN of 2023-10-25 drew 811 points and 102 comments, and the GitHub repo carried 4.3k stars and 86 forks at the 2026-09-04 crawl. The README by then announced that a new and final version had been rewritten from scratch, pointing to Demystify.
Demystify expands the same idea across surfaces: automatic path-parameter identification, a desktop app that proxies traffic (in the spirit of mitm2swagger), a website and CLI that generate specs from HAR files (har-to-openapi style), a published library for middleware and DevOps, curl and client-code generation, and the ability to translate between OpenAPI versions or reverse-engineer other HTTP standards such as GraphQL. No company, funding or revenue is documented in the material.
What has to be true
- Verifiable attention: the 2023-10-25 Show HN drew 811 points and 102 comments (item 38012032), and the repo showed 4.3k stars and 86 forks at the 2026-09-04 crawl.
- The bet is concrete: watch real network traffic and merge observations into a spec, so API discovery no longer depends on docs that are missing, wrong or internal-use only.
- The material records follow-through: the README's 'Important' note announces a from-scratch rewrite (Demystify) that becomes desktop app, CLI, website and library, not just the extension.
- It stays honest about scope: the extension merges what it observes and records unknowns such as nullable values rather than guessing, a design choice documented in the README.
What can be applied
When docs are the bottleneck, generate them from observed behavior: real traffic never goes stale the way written specs do, and the output unlocks clients, tests and integrations downstream.
Aftermath
As of 2026-09-05 the original repo is live at 4.3k stars and 86 forks, and its README directs users to Demystify (github.com/AndrewWalsh/demystify), a suite generating OpenAPI 3.1 specs in real time from live traffic or HAR files: a desktop proxy app, browser extension, CLI (npx demystify --input file.har) and the demystify-lib library, plus GraphQL support. No company, funding or revenue is documented in the material, so commercial status remains unverified; what is documented is evolution from a 2023 Show HN extension into a broader API-documentation toolchain.
Sources
- Show HN: OpenAPI DevTools – Chrome extension that generates an API spec
- AndrewWalsh/openapi-devtools — README (4.3k stars at crawl)
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