A load testing tool for measuring Core Web Vitals (LCP, FCP, CLS, TTFB) across your web application. Built with a Go backend, React frontend, and k6 browser module for real browser-based measurements.
| Discover Routes | Select Routes |
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| Configure Test | Run History |
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- Discover routes -- crawl a site automatically (with auth support), browse interactively, or enter routes manually
- Configure the test -- set virtual users, duration, ramp stages, and think time
- Run -- k6 launches headless Chromium instances that navigate each URL and collect Web Vitals via the Performance Observer API
- Monitor -- live dashboard streams metrics over WebSocket as the test runs
- Review -- results are persisted to SQLite with p50/p75/p95 breakdowns per URL
| Tool | Required | Purpose |
|---|---|---|
| Go 1.22+ | Yes | Backend |
| Node.js 18+ | Yes | Playwright scripts, frontend build |
| k6 | Yes | Test runner |
| air | No | Hot reload for dev |
# Install all dependencies (Go modules, Node packages, Playwright Chromium)
make setup
# Start dev servers (backend :8080 + frontend :5173)
make devOpen http://localhost:5173.
make build produces a single self-contained binary at bin/load-test with the React frontend embedded.
make build
./bin/load-test # serves UI + API on :8080
./bin/load-test -port 3000 # custom port
./bin/load-test -script path/to.js # custom k6 scriptcmd/server/ Go entry point, embedded frontend
internal/
api/ REST handlers, WebSocket hub, routing
auth/ Auth config types (cookie, bearer, headers)
crawler/ Route discovery (HTML crawl, sitemap, Playwright browser)
k6/ k6 runner, NDJSON parser, metric aggregator
recorder/ Login step recorder (Playwright)
routes/ Route pattern expansion
store/ SQLite persistence
scripts/
web-vitals.js k6 browser test script (the actual load test)
crawl-authenticated.mjs Headless site crawler with auth
discover-interactive.mjs Interactive browser-based route discovery
record-login.mjs Login flow recorder
frontend/ React + Tailwind + Recharts UI
| Method | How it works |
|---|---|
| Auto crawl | Fetches HTML, parses links, optionally checks sitemap.xml. Supports authenticated crawl via cookies/bearer/headers. |
| Interactive | Opens a real browser window -- browse around your site, close the tab when done. Captures SPA navigation (pushState/replaceState). |
| Manual | Enter URL patterns directly (e.g. /users/:id) with parameter values for expansion. |
The tool supports three auth modes for both crawling and load testing:
- Cookie -- Records login form interactions, replays them to establish a session
- Bearer -- Injects an
Authorization: Bearer <token>header - Custom headers -- Passes arbitrary headers with each request
| Metric | k6 Name | Description |
|---|---|---|
| Largest Contentful Paint | custom_lcp |
Time until the largest visible element renders |
| First Contentful Paint | custom_fcp |
Time until the first text/image renders |
| Cumulative Layout Shift | custom_cls |
Visual stability score (lower is better) |
| Time to First Byte | custom_ttfb |
Server response time |
| Page Errors | page_errors |
JavaScript error count |
| Success Rate | page_success_rate |
Percentage of pages that loaded without errors |
| Target | Description |
|---|---|
make setup |
Install all dependencies and verify the build |
make dev |
Start backend + frontend dev servers |
make build |
Production build (single binary with embedded frontend) |
make test |
Run E2E tests |
make test-screenshots |
Capture UI screenshots across viewports |
make clean |
Remove build artifacts and database |
make check |
Verify required tools are installed |
The k6 test is configured entirely through the UI. Under the hood, the Go backend passes configuration to k6 via environment variables:
| Variable | Description |
|---|---|
URLS_JSON |
JSON array of target URLs |
STAGES_JSON |
k6 ramping-vus stage definitions |
AUTH_JSON |
Auth configuration object |
THINK_TIME |
Seconds between page visits per VU |
K6_BROWSER_ENABLED |
Always set to true by the runner |
MIT