Test every error state
Return a 500, 401 or 429, an empty list or a broken payload, and see how your UI copes. Failed saves too: POST, PUT and DELETE.
Chrome extension for frontend developers
Mock any API response in your browser
Override, block or redirect requests with simple URL rules, for any HTTP method. Test error states and build before the backend is ready. Your rules never leave your device.
Coming Soon to Chrome
See Pricing
Free to use. 6 rules with a free account, no credit card.
Why developers use it
Change what the browser receives, not the backend
Build before the API exists
Mock the endpoint you need with the JSON you expect and keep working while the backend catches up.
Reproduce bugs exactly
Paste the payload from a bug report and replay it on your local or staging app, as often as you like.
Swap or silence scripts
Point a production script at your local build, or block analytics and third-party widgets while you develop.
Features
Everything you need to fake an API, nothing you don't
No proxy to install, no certificates, no API client. Just rules that run inside Chrome.
Override any response
Replace the body and status code of fetch and XHR calls, for GET, POST, PUT, PATCH, DELETE and more.
Mock without a server
Serve the response without sending the request at all, or let the real request go and only change what comes back.
Block and redirect
Block requests or redirect them to another URL. Works for scripts, CSS, images, frames and workers too.
Folders and priority
Group rules into folders, switch a whole folder on or off, and drag to reorder. The first matching rule wins.
Contains or regex
Match URLs by a simple substring or a regular expression, optionally only for the methods you choose.
Import from Requestly
Switching tools? Import your existing response rules in one click: groups become folders and priority is kept.
Set up in under a minute
- Add a rule. Paste part of the URL you want to change, or a regex.
- Choose what happens. Override the response, block the request or redirect it.
- Use your app. Changes apply to open tabs at once. No reload, no proxy, no certificates.
Private by design
Your rules stay on your device
Rules and response bodies live in your browser's extension storage. The server only knows your email address and your plan, so it can tell the extension which limits apply.
Read the Privacy Policystoragekeeps your rules and settings in your browser.declarativeNetRequestblocks and redirects requests inside Chrome.alarmsrefreshes your plan in the background, about once a day.- Access to http and https pages lets rules apply to the sites you test. The extension doesn't read or record what you browse.
Pricing
Simple plans, fair prices
Start free. Upgrade when you need more rules running at once.
Launch offer
The first 500 customers pay 40% less than the regular price, and keep that price for as long as they stay subscribed.
Free
For trying it out and the odd mock.
$0
no card needed
- 6 rules
- 3 active at once
Coming Soon to Chrome
Free needs a free account (email code, no password). Without one: 3 rules, 1 active at once.
Basic
For everyday frontend work.
$18
/ year
$1.50 a month, billed yearly
Launch price. $30 / year after the first 500 customers.
$2.99
/ month
billed monthly, cancel anytime
Launch price. $4.99 / month after the first 500 customers.
- 15 rules
- 8 active at once
Available Soon
Pro
No limits, for heavy mocking and QA.
$36
/ year
$3 a month, billed yearly
Launch price. $60 / year after the first 500 customers.
$5.99
/ month
billed monthly, cancel anytime
Launch price. $9.99 / month after the first 500 customers.
- Unlimited rules
- All active at once
Available Soon
Every plan includes
- Override responses for any HTTP method
- Block and redirect requests
- Folders, priority and regex
- Import from other tools
- JSON import and export
- Rules stay on your device
Prices in US dollars (euro prices use the same numbers) and include VAT or sales tax where it applies. Paid plans open shortly after launch. See the Refund Policy.
FAQ
Questions, answered
Is it safe? What data does it collect?
Your rules are stored only in your browser and are never sent to our servers. Your account holds just your email address and your plan. The extension doesn't read or collect your browsing history, and it contains no ads or trackers. The Privacy Policy lists everything.
Which requests can it change?
Override rules change fetch and XMLHttpRequest calls made by the page and its frames. Block and redirect rules work in Chrome's network stack, so they also cover scripts, CSS, images, frames and workers. Page navigations aren't changed.
Does it work on localhost and staging?
Yes. Rules apply to any http or https page, including localhost, staging servers and production sites.
Why does DevTools still show the original response?
The extension changes the response the page's code receives, after Chrome has recorded the request. Every override is logged to the page console as [Placebo API] so you can check it.
Why would I need an account?
You don't, to try it: without an account you get 3 rules with 1 active. A free account (an email and a 6-digit code, no password) raises that to 6 rules with 3 active and is how paid plans are unlocked. Your rules still stay on your device.
Which browsers are supported?
Chrome 111 or newer, and Chromium browsers that install from the Chrome Web Store, such as Edge, Brave and Arc. Firefox isn't supported yet.
Can I cancel a paid plan?
Yes, any time. You keep the plan until the end of the period you paid for, and your rules are never deleted when a plan ends. See the Refund Policy for refunds.
Something else? Write to support@placeboapi.com.
Stop waiting for the backend
Install Placebo API and mock your first response in under a minute.
Coming Soon to Chrome