Cron Expression Generator
Pick when a job should run and get a valid cron expression with its next run times.
Free developer tools
Twenty free tools for the jobs, webhooks and infrastructure that break quietly. No sign-up, and most run entirely in your browser.
- 20 tools
- Free
- No sign-up
Cron jobs
5 toolsBuild, read and lint cron schedules, then make sure jobs report in when they run.
Cron Expression Parser
Translate a cron expression into plain English and list its next runs in any time zone.
Crontab Validator
Check a whole crontab for syntax errors and the mistakes that make jobs fail silently.
Cron Heartbeat Calculator
Get the expected interval and grace period to monitor a cron job without false alarms.
Heartbeat Ping Snippet Generator
Wrap any command so it pings a heartbeat URL on success and reports failures.
Webhooks
5 toolsCapture, verify and design webhooks, and plan what happens when a delivery fails.
Webhook Tester
Get a temporary URL and inspect the headers and body of every webhook sent to it.
Webhook Signature Verifier
Check an HMAC webhook signature for Stripe, GitHub, Shopify, Slack or your own scheme.
Webhook Retry Calculator
See when each retry fires with exponential backoff and jitter, and what survives an outage.
Webhook Payload Examples
Sample payloads and headers for Stripe, GitHub, Shopify, Slack, Twilio and Zapier.
Slack & Discord Webhook Tester
Compose, preview and send a test message to a Slack or Discord incoming webhook.
Developer tools
5 toolsEveryday encoders, decoders and references for working with APIs.
JSON Formatter
Pretty-print, minify and validate JSON with exact line and column errors.
JWT Decoder
Read a JWT’s header and claims, check expiry and verify HMAC signatures locally.
Unix Timestamp Converter
Convert epoch timestamps to dates and back in any time zone, with unit detection.
Base64 Encoder / Decoder
Encode and decode Base64 and URL-safe Base64, including files and Basic Auth headers.
HTTP Status Code Lookup
What each HTTP status code means, whether to retry it and whether it’s healthy.
Cloud, uptime & domains
5 toolsCheck certificates, domains, DNS and headers, and see what an uptime target really allows.
SSL Certificate Checker
See who issued a site’s certificate, when it expires and which hostnames it covers.
Domain Expiry Checker
Look up a domain’s expiry date, registrar, status and name servers via RDAP.
HTTP Headers Checker
Follow a URL’s redirects, list its response headers and grade its security headers.
DNS Lookup
Query A, AAAA, CNAME, MX, TXT, NS, CAA and SOA records over DNS-over-HTTPS.
Uptime & SLA Calculator
Turn an uptime percentage into allowed downtime, or downtime into an uptime percentage.
Tools tell you what’s wrong now. SensaCat tells you the moment it breaks.
Monitor cron jobs, webhooks, multi-step business flows, certificates and domains, and alert your team before customers notice.