JavaScript error monitoring for the browser.

Q: What does the browser SDK capture on its own?

After init() it captures uncaught errors from the window error event and unhandled promise rejections, and it records Core Web Vitals and session replay. console.error calls become events only when you set captureConsoleErrors: true.

Q: Does it work with React, Vue, or plain JavaScript?

Yes, it only needs a browser. React render errors need SquasherErrorBoundary from @squasher-ai/browser/react. Vue handles component errors itself, so call captureError from app.config.errorHandler. For Next.js, use the Next.js setup.

Q: Are minified stack traces readable?

Yes, when you upload source maps. Upload them for each release with the CLI, and the issue page shows the original file, line, function, and source lines. Maps with a debug ID match without a release.

Q: Will it slow my page down?

Errors are sent one by one with sendBeacon or a keepalive fetch, and Web Vitals in small batches. The replay recorder is the largest part. It is loaded with a dynamic import, and with replay: { enabled: false } it is not loaded at all.

Q: How do I keep personal data out?

Use beforeSend to change or drop an event before it leaves the page. Replay masks all text, typed values, and media by default; hide more elements with privacy.blockSelector.

Q: How do I know which user hit an error?

Call identify() or setUser() after sign-in. Later events carry that user, and replays are attributed to the same identity.

Add @squasher-ai/browser and call init() once. Uncaught errors, unhandled rejections, Web Vitals, and session replay start on their own.

Start free

Free plan. No credit card required.

import { init } from "@squasher-ai/browser"; init({  apiKey: import.meta.env.VITE_SQUASHER_API_KEY,  projectId: import.meta.env.VITE_SQUASHER_PROJECT_ID,  environment: import.meta.env.MODE,  release: import.meta.env.VITE_GIT_SHA,  captureConsoleErrors: true,});

app.squasher.ai/acme/checkout-web/issues

TypeError: Failed to fetch

UnhandledRejection(TypeError)

MediumUnresolvedError

Events: 312
First seen: 2d ago
Last seen: 4m ago
Environment: production
Service: checkout-web

Example code and the issue it produces.

What is automatic, and what you add.

One init() call covers what the browser reports on its own. The rest is one line each.

Uncaught errors

Captured: Automatic
How: The window error event, with stack frames and the page URL.

Unhandled rejections

Captured: Automatic
How: Recorded as UnhandledRejection, with the original error type.

Core Web Vitals

Captured: Automatic
How: LCP, CLS, INP, FCP, and TTFB.

Session replay

Captured: Automatic
How: On by default, with password fields masked. Set a sample rate.

console.error calls

Captured: Opt in
How: Set captureConsoleErrors: true.

React render errors

Captured: When wrapped
How: SquasherErrorBoundary from @squasher-ai/browser/react.

Errors you catch

Captured: Manual
How: captureError(error, extra).

What the Squasher browser SDK captures on its own, and what needs one line of code.
Signal	Captured	How
Uncaught errors	Automatic	The window error event, with stack frames and the page URL.
Unhandled rejections	Automatic	Recorded as UnhandledRejection, with the original error type.
Core Web Vitals	Automatic	LCP, CLS, INP, FCP, and TTFB.
Session replay	Automatic	On by default, with password fields masked. Set a sample rate.
console.error calls	Opt in	Set captureConsoleErrors: true.
React render errors	When wrapped	SquasherErrorBoundary from @squasher-ai/browser/react.
Errors you catch	Manual	captureError(error, extra).

Checked with @squasher-ai/browser 0.4.0 on September 24, 2026.

Live in three steps.

Install the SDK, start it when your app boots, and throw one error. Or paste one prompt into your coding agent.

Install the browser SDK
Install it in the app that runs in the browser.
```
npm install @squasher-ai/browser
```

Call init() once at startup

Read the key and project ID from your bundler's public environment variables.

import { init } from "@squasher-ai/browser"; init({  apiKey: import.meta.env.VITE_SQUASHER_API_KEY,  projectId: import.meta.env.VITE_SQUASHER_PROJECT_ID,  environment: import.meta.env.MODE,  release: import.meta.env.VITE_GIT_SHA,  captureConsoleErrors: true,});

Throw one test error
Run this in the page, then check Issues in your project.
```
setTimeout(() => {  throw new Error("Squasher test error");});
```
Browser SDK guide

Paste into your coding agent

Install Squasher for this project. If Squasher skills or MCP are not configured in this agent environment, run `bash <(curl -fsSL https://squasher.ai/install.sh) --agents -y`. Then read https://skills.squasher.ai/squasher-onboard/SKILL.md, map every runnable app/service/worker/frontend/agent in the repo, choose the matching Squasher SDK, log drain, OTLP, or Agent SDK path, initialize with SQUASHER_API_KEY and SQUASHER_PROJECT_ID from environment variables, send one real verification event, and report the files changed plus the verification step. Do not hardcode or reveal real API keys.

bash <(curl -fsSL https://squasher.ai/install.sh) --agents -y

See what the user saw.

Replay records the page as the user used it. It shares a session ID with that user's errors.

On by default after init(). Password fields are always masked.
Mask all text, or block elements by CSS selector.
Record a share of sessions with replay.sampleRate.
Turn it off with replay: { enabled: false }.

How session replay works

shop.example.com/checkout

Total

Pay

Something went wrong

error at 1:031:40

Example replay.

Context on every event.

A stack trace says where the code failed. These fields say which build, which page, and which user.

Release
The build the error came from. Pass your commit SHA to release.
Environment
production, staging, or development, so you can filter issues.
Page URL
The address of the page where the error happened.
Session ID
One ID per browser tab, shared by errors, Web Vitals, and replay.
User
Call identify() after sign-in, and later events carry that user.
beforeSend
Change or drop any error event before it leaves the page.

Source maps, uploaded per release.

Build with source maps and upload them from CI with the release you deploy.

Squasher stores the maps by project, service, and release.
Stack traces are not de-minified with them yet.
Keep .map files off your public host if you do not want to publish your source.

Source map docs

CI after the build

vite build --sourcemap squasher sourcemaps upload \  --project "$SQUASHER_PROJECT_ID" \  --service checkout-web \  --release "$GIT_SHA" \  $(find dist -name "*.map")

Common JavaScript errors, explained.

What each error means in every browser, why it happens, and the code that fixes it.

TypeError: Failed to fetch
No response reached your code: CORS, offline, or blocked.
Read the fix
Cannot read properties of undefined
A value was never set: data not loaded, or a failed find().
Read the fix
Cannot read properties of null
A DOM query, ref, or match() returned null.
Read the fix
ResizeObserver loop limit exceeded
A resize callback changed the size it was watching.
Read the fix
JavaScript network error
fetch, Axios, and chunk loads that fail before a response.
Read the fix
Stack trace parser
Paste a JavaScript, Python, JVM, Ruby, or Go stack trace and find the first app frame.
Open the tool

Questions, answered.

What does the browser SDK capture on its own?

After init() it captures uncaught errors from the window error event and unhandled promise rejections, and it records Core Web Vitals and session replay. console.error calls become events only when you set captureConsoleErrors: true.

Does it work with React, Vue, or plain JavaScript?

Yes, it only needs a browser. React render errors need SquasherErrorBoundary from @squasher-ai/browser/react. Vue handles component errors itself, so call captureError from app.config.errorHandler. For Next.js, use the Next.js setup.

Are minified stack traces readable?

Yes, when you upload source maps. Upload them for each release with the CLI, and the issue page shows the original file, line, function, and source lines. Maps with a debug ID match without a release.

Will it slow my page down?

Errors are sent one by one with sendBeacon or a keepalive fetch, and Web Vitals in small batches. The replay recorder is the largest part. It is loaded with a dynamic import, and with replay: { enabled: false } it is not loaded at all.

How do I keep personal data out?

Use beforeSend to change or drop an event before it leaves the page. Replay masks all text, typed values, and media by default; hide more elements with privacy.blockSelector.

How do I know which user hit an error?

Call identify() or setUser() after sign-in. Later events carry that user, and replays are attributed to the same identity.

On squasher.ai

In the docs

Priced by volume, never by seat.

Start free. Invite the whole team. AI triage is included on every plan.

Compare every plan

Free

For side projects, evals, and internal tools.

$0/ month

No card needed. No overage charges.

10 GB telemetry
5K replays
500 AI credits

Included

AI triage on new issues
500 AI credits / month (an investigation uses 50)
1 project

Pro

For small production apps that want one tool, not five.

$29/ month

Flat price. No per-seat fees.

100 GB telemetry
10K replays
3K AI credits

Everything in Free, plus

3,000 AI credits / month (an investigation uses 50)
5 projects
30 monitors with 30-second checks

Team

Scale

For high-volume teams with security, procurement, and support needs.

$299/ month

Flat price. No per-seat fees.

1 TB telemetry
150K replays
30K AI credits

Everything in Team, plus

30,000 AI credits / month (an investigation uses 50)
100 status pages
250 monitors with 30-second checks

Need more volume, a security review, or custom terms? Get in touch.

Go squash some bugs.

Connect one service and send one real event. The crew takes it from there.

Start free

Free plan. No credit card required.

JavaScript error monitoring for the browser.

What is automatic, and what you add.

Uncaught errors

Unhandled rejections

Core Web Vitals

Session replay

console.error calls

React render errors

Errors you catch

Live in three steps.

Install the browser SDK

Call init() once at startup

Throw one test error

See what the user saw.

Context on every event.

Release

Environment

Page URL

Session ID

User

beforeSend