Developer Utilities

Regex Tester, Cron Builder, Chmod Calculator, Subnet Calculator and Git Reference

The small lookups and conversions that interrupt a working day. Test a regex against real input, build a cron schedule without counting fields, work out what 755 means, convert a timestamp, decode a user-agent string, split a CIDR range, or check a domain's DNS records. Each tool does its one job and gets out of the way.

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IP Address Info

Classify any IPv4 or IPv6 address and see its every form.

Every Dev Utilities tool

CHMOD Calculator

Convert Unix permissions between rwx, octal and symbolic.

CSS Selector Tester

Test a CSS selector against pasted HTML and list every matching element.

Core Web Vitals Calculator

Check whether your page passes Core Web Vitals and which metric to fix first.

DNS Lookup

Query any DNS record for a domain with TTLs and explanations.

HTTP Status Codes

Look up what any HTTP status code actually means.

IP Address Info

Classify any IPv4 or IPv6 address and see its every form.

Image Size Calculator

Estimate image file size and see how oversized it is for its slot.

Keycode Tester

Press a key and see exactly what your browser reports.

Regex Generator

Build a regex from a preset or from sample strings, ready to paste.

SemVer Tool

Sort, compare and bump semantic version numbers.

What Is My IP

See the public IP address every website sees when you connect.

Base Converter

Convert numbers between binary, octal, decimal and hex.

CURL Converter

Turn a curl command into code in 24 languages.

Patterns and schedules

The regex tester highlights matches and capture groups as you type, with flags, a replacement preview and an explanation of each token. The regex generator builds a pattern from a description of what you want to match, for the cases where you know the shape but not the syntax. The cron builder turns "every weekday at 9" into the five-field expression and, more usefully, turns an expression you found in a crontab back into English along with the next few run times.

Permissions, versions and git

The chmod calculator converts between octal, symbolic and checkbox views of Unix file permissions. Semver checks whether a version string is valid, compares two, and shows which versions a range like ^1.4.0 actually allows. The git command reference is a searchable list of the commands people look up most, with the flags that matter.

Numbers and time

Epoch converter translates Unix timestamps in seconds, milliseconds or nanoseconds to readable dates in UTC and your local zone, and back. Base converter moves numbers between binary, octal, decimal and hex, including negative and fractional values.

HTTP and browsers

HTTP status codes is a reference with the meaning, typical cause and correct usage of each code. Keycode shows the key, code and legacy keyCode for whatever you press. The user-agent parser identifies the browser, engine, OS and device from a UA string. Curl converter turns a curl command into fetch, Python requests, Go or PHP, and URL query parser breaks a long URL into its parameters so they can be read and edited individually.

Networks

The IP subnet calculator takes an address and prefix and gives the network, broadcast, usable range and mask, and can split a block into smaller subnets. DNS records looks up A, AAAA, CNAME, MX, TXT and NS records for a domain; it is the one tool here that makes a network request, to a public DNS-over-HTTPS resolver, because the answer has to come from somewhere.