Web Utilities
23 free toolsTest webhooks, inspect requests, build URLs, and debug the HTTP layer.
Web utilities are the debugging tools around HTTP: send a test request, catch a webhook, inspect a HAR file, parse or build a URL with UTM parameters, look up a status code, and convert curl commands. They are meant for the moment an integration fails and you need to see exactly what was sent and what came back.
Most of these run in your browser; the HTTP request builder and webhook tester send requests through our server so they work around CORS, and nothing is stored.
All 23 tools
Timestamp Converter
Convert between Unix timestamps and human-readable dates
URL Parser
Break a URL into its components
HTTP Status Code Reference
Searchable list of HTTP status codes
Meta Tag Generator
Generate HTML meta tags, Open Graph, and Twitter Card tags
Cron Expression Parser
Parse cron expressions into human-readable descriptions
Epoch Batch Converter
Convert a list of Unix timestamps to human-readable dates
Timezone Converter
Convert a date and time between time zones
Duration Calculator
Time and business days between two dates
Date Format Converter
Convert a date between ISO, Unix, RFC, and more
Countdown Timer
Live countdown to any future date
Pomodoro Timer
Work/break cycle timer with configurable rounds and tab-title countdown
Stopwatch
Precise stopwatch with lap splits, centiseconds, and keyboard shortcuts
Wheel Spinner
Spin an animated wheel to pick a random name or item from your list
OG / Social Card Preview
Preview Open Graph and Twitter Card meta tags with live social previews
OG Image Generator
Design a 1200×630 Open Graph social share image and download it as PNG
MIME Type Reference
Look up MIME types by file extension — searchable content-type reference
Browser Fingerprint Inspector
See the fingerprint signals your browser exposes — locally, nothing transmitted
CSP Header Builder
Build Content Security Policy headers with a visual form
Webhook Tester
Send test POST requests to webhook endpoints and inspect responses
WebSocket Tester
Connect to WebSocket endpoints, send messages, and inspect the session
HTTP Request Builder
Send HTTP requests and inspect responses — a lightweight online API client
Design System Extractor
Extract colors, fonts, spacing, and shadows from any website as design tokens
HAR File Viewer
Open DevTools .har exports privately — waterfall, timings, headers, and copy-as-curl
Guides
From the blog: the mechanisms, standards, and edge cases behind these tools.
- ISO 8601 vs RFC 3339: Which Timestamp Format Should Your API Return? RFC 3339 is a strict profile of ISO 8601. Eight timestamps checked against both, plus the no-offset string that is valid in one and ambiguous in the other. Oct 15, 2026 · uses Epoch Batch Converter, Timezone Converter, Duration Calculator +1
- How to Test Discord and Slack Webhooks (Without Writing Code) The exact JSON payloads both platforms expect, what each status code means, why 204 looks like a failure, and how to debug rate limits, invalid_payload, and no_service errors. Jul 25, 2026 · uses HTTP Status Code Reference, Webhook Tester, WebSocket Tester +1
- YYYY vs yyyy: The Week-Year Bug That Ships in December YYYY vs yyyy: in date-fns, Java and ICU, YYYY is the week-based year, not the calendar year — it prints 2027-12-31 for Dec 31, 2026. Plus a token cheat sheet. Sep 7, 2026 · uses Cron Expression Parser, Timezone Converter, Date Format Converter
- Should You Store Timestamps in UTC? Yes — Except Future Local-Time Events Why "store UTC, display local" is the right default for recording instants, and the exception that corrupts calendars: future events defined in local time need a wall time plus an IANA zone name, because governments really do rewrite timezone rules with weeks of notice. Aug 19, 2026 · uses Cron Expression Parser, Timezone Converter, Countdown Timer
- CORS Errors Explained: Why curl Works and fetch Doesn't The server got your request. The browser just won't let your JavaScript read the reply. What preflight is, the three wrong fixes, and the missing header. Oct 16, 2026 · uses Webhook Tester, HTTP Request Builder
- HTTP Status Codes: The Reference You Actually Use, With the SEO Ones Flagged The HTTP status codes developers actually meet, by class, plus the confusing pairs: 301 vs 308, 404 vs 410, 401 vs 403, 429, 503 and soft 404s. Oct 16, 2026 · uses HTTP Status Code Reference, HTTP Request Builder
- Secret Santa Without a Hat: Derangements, Exclusions, Private Links Drawing names from a hat fails about 63% of the time with 5+ people. The math of derangements, when couple exclusions make a draw impossible, and how reveal links work. Oct 15, 2026 · uses Countdown Timer, Wheel Spinner
- Why Your WebSocket Keeps Disconnecting: Reading Close Codes 1000–1015 Code 1006 with an empty reason is the most common WebSocket failure and the least explained. How the close handshake actually works, the full RFC 6455 close-code table, which codes are never allowed on the wire, and why an idle proxy is probably killing your connection at the 60-second mark. Aug 20, 2026 · uses WebSocket Tester, HTTP Request Builder
- Content-Type: Why Your File Downloads Instead of Opening The browser does not care about your file extension. What Content-Type actually controls, how MIME sniffing turns a wrong header into an XSS bug, and the extensions where the canonical type is genuinely contested. Jul 29, 2026 · uses HTTP Status Code Reference, MIME Type Reference
- How to Read a curl Command: Every Flag You Will Actually See A field guide to the curl flags that show up in the wild — -d vs --data-raw vs --data-binary, when -d silently makes it a POST, what -L does to your method on a redirect, and why -k is never the fix. Jul 27, 2026 · uses HTTP Status Code Reference, HTTP Request Builder
- Open Graph Image Sizes in 2026: One File That Works Everywhere The 1200×630 standard, the safe zone that survives every crop, the meta tags you actually need, and why X strips your headline — plus how to debug a preview that refuses to update. Jul 25, 2026 · uses OG / Social Card Preview, OG Image Generator
- Unix Timestamps and Epoch Time Explained (Plus the Year 2038 Problem) What a Unix timestamp actually is, why "the epoch" is 1970, how seconds vs milliseconds trips people up, timezones, and the Year 2038 problem — with tools to convert epoch values instantly. Jul 17, 2026 · uses Epoch Batch Converter, Duration Calculator