What Mock API Studio does
Paste JSON or an OpenAPI spec and get live HTTPS CRUD endpoints with realistic data, so your frontend can be built before the backend exists.
The frontend usually waits on the backend. You hard-code fixtures into components, then rewrite every call when the real API finally lands. Mock API Studio gives you the real thing early: an HTTPS base URL your app calls with fetch or axios exactly as it will call production, so swapping to the real backend is a one-line change in .env.
Paste a JSON example and you have an API. Every top-level array becomes a resource with GET, POST, PUT, PATCH and DELETE, and the changes persist: create a user with POST and it is there on the next GET, delete it and you get a 404. Field names drive the fake data, so email fields get addresses, avatar fields get image URLs, price fields get prices and createdAt gets dates. Your own sample records stay at the top of the list.
Already have an OpenAPI 3 spec? Drop the YAML or JSON file. Collection and item paths become resources, schemas become typed fields, examples become sample records, and anything that is not plain CRUD is listed as skipped with the reason, so you know exactly what was mocked.
The API behaves like a real one. Lists support ?page and ?limit with an X-Total-Count header, ?sort and ?order, equality filters such as ?status=active, range filters such as ?price_gte=10, and ?q for full-text search. Typed fields are validated, so a POST with a number in an email field returns 422 naming the field. CORS allows any origin and answers preflight requests, so localhost and preview deploys just work.
Watch every call land. The live request log shows method, path, status, time and the origin that called, and the data grid updates the moment your app writes. Edit any cell in the grid and the next GET returns the new value. Pro adds what you need to test loading and error states: latency, random failures, forced status codes and an Authorization check, for $5 a month.
Free vs Pro
| Feature | Free $0 · no account | Pro $5/mo · 3 browsers |
|---|---|---|
| 1 project with up to 4 resources and 100 records per resource | Included | Included |
| Create resources by pasting JSON (arrays and objects are inferred), from a field table, or by importing an OpenAPI 3 JSON or YAML file | Included | Included |
| Realistic seed data picked from field names and formats (email, name, avatar, price, createdAt, uuid and 50 more), reproducible from a fixed seed | Included | Included |
| Stateful CRUD: GET list and one, POST, PUT, PATCH, DELETE, with page, limit, sort, order, field filters and q full-text search | Included | Included |
| Permissive CORS for localhost and preview deploys, consistent JSON errors (400, 404, 422, 429) that name the field | Included | Included |
| Live request log of the last 100 calls and an editable data grid that updates as your app writes | Included | Included |
| Copy fetch, curl and axios snippets or a .env line; reset to seed in one click | Included | Included |
| 1,000 requests per day per project; data is cleared after 14 days without requests and restored when you reopen it | Included | Included |
| 10 projects, 50 resources each, 5,000 records per resource | — | Pro |
| 20,000 requests per day per project, and data is never cleared for being idle | — | Pro |
| Latency injection (fixed or random, up to 2,000 ms) and error-rate injection (500, 502 or 503) | — | Pro |
| Route rules: force a status, override the body, or require an Authorization header (401 without it) | — | Pro |
| Relations: belongs-to fields with ?_expand=parent and nested /users/1/posts listings | — | Pro |
| Share a live read-only link or an editor link with teammates | — | Pro |
| Export the whole project as JSON and import it into a new project | — | Pro |
Pro is $5/mo, billed monthly. Checkout and the licence key are handled by Dodo Payments (merchant of record). By buying you agree to the Terms and Privacy Policy.
Questions
Is Mock API Studio free?
Yes, with no account and no install. The free plan includes: 1 project with up to 4 resources and 100 records per resource; Create resources by pasting JSON (arrays and objects are inferred), from a field table, or by importing an OpenAPI 3 JSON or YAML file; Realistic seed data picked from field names and formats (email, name, avatar, price, createdAt, uuid and 50 more), reproducible from a fixed seed; Stateful CRUD: GET list and one, POST, PUT, PATCH, DELETE, with page, limit, sort, order, field filters and q full-text search; and 4 more. Pro ($5/mo, billed monthly, cancel anytime) adds: 10 projects, 50 resources each, 5,000 records per resource; 20,000 requests per day per project, and data is never cleared for being idle; Latency injection (fixed or random, up to 2,000 ms) and error-rate injection (500, 502 or 503); Route rules: force a status, override the body, or require an Authorization header (401 without it); and 3 more.
Does Mock API Studio upload my data?
Yes, by design. Your project definition, its generated records and a log of the last 100 requests (method, path, status, duration, time and the calling site's host; no bodies or headers) are stored in Google Firebase in the United States so your endpoints answer while this tab is closed. A free project's data is cleared after 14 idle days and the project is deleted after 60. You can delete a project at any time. See the Privacy Policy for retention and deletion.
Do I need to install anything?
No. Open the page and start working. It works on desktop and mobile browsers.
How does the Pro licence work?
Pro is a monthly subscription handled by Dodo Payments (our merchant of record). You receive a licence key by email and paste it under "Have a key?" inside the tool. One key works on up to 3 browsers.
Does the API keep my changes?
Yes. POST, PUT, PATCH and DELETE change the stored data, and the data grid on the page shows each change live. Reset to seed restores the original generated records exactly, because the seed is fixed per project.
What does the URL look like?
https://tools.cosmovexapps.com/mock/{projectId}/{resource} for lists and /{resource}/{id} for one record. Lists accept ?page, ?limit, ?sort, ?order, ?q and field filters like ?status=active or ?price_gte=10.
Does it work from localhost and preview deploys?
Yes. Every response sends Access-Control-Allow-Origin: * and preflight OPTIONS requests are answered, including custom headers such as Authorization.
Can I import an OpenAPI or Swagger file?
OpenAPI 3.0 and 3.1 in YAML or JSON. Paths like /pets and /pets/{id} become a pets resource with fields from its schema. Swagger 2.0 files need converting to OpenAPI 3 first; the importer tells you which paths it skipped and why.
Do endpoints expire?
Free projects keep working as long as they are called. After 14 days without requests their data is cleared, and it is restored automatically when you open the project again. A free project with no requests for 60 days is deleted. Pro projects are never cleared for being idle.
Why is Pro a subscription?
Your mock API answers your app around the clock, even when this page is closed, and that is a real running cost. Pro is $5 a month and you can cancel any time.
Do I need an account?
No. Projects belong to this browser through an anonymous session. Keep the base URL somewhere safe; Pro users can export a project to a file and import it anywhere.
