Free Developer Tools
The utilities you reach for mid-task: a regex tester with plain-English explanations, a cron expression builder with next-run times, a JWT decoder, SHA hash and checksum generation, JSON ⇄ YAML ⇄ CSV conversion, a WCAG contrast checker, a URL inspector, a Markdown editor, an exact subnet/CIDR calculator, a seeded fake-data generator and JSON-to-code type generation for TypeScript, Go, Rust and more.
Everything runs locally, which is not a nicety here — it is a security requirement. Tokens, connection strings, proprietary payloads and customer data pasted into these tools never leave your machine, so they are safe to use with real production values. No accounts, no telemetry, no “pro tier” hiding the useful half of the tool.
Regex Tester & Explainer
Free online regex tester with live highlighted matches, capture groups, replace preview, a plain-English explainer and JSON/CSV match export.
JWT Decoder
Decode and inspect JWTs entirely in your browser — header, payload, expiry. Nothing leaves your device.
Cron Expression Builder
Build and decode cron schedules in plain English, with the next run times.
JSON ⇄ YAML ⇄ CSV Converter
Convert between JSON, YAML and CSV instantly, with validation and pretty-print.
Subnet Calculator — IPv4, CIDR & Mask
Free IPv4 subnet calculator — network & broadcast address, host ranges, wildcard mask, binary breakdown, subnet splitting. Exact 32-bit math.
JSON to Code (TypeScript, Go, Rust…)
Paste JSON and get strongly-typed definitions in TypeScript, Go, Rust, Python, Kotlin, C# and JSON Schema — deterministic, instant and private.
URL Encoder & Inspector
Encode/decode URLs and break any URL into its parts and query params.
WCAG Contrast Checker
Check colour contrast for accessibility — AA/AAA pass-fail with live preview.
Hash & Checksum Generator
Generate SHA-1/256/384/512 hashes of text or files, in your browser.
Markdown Editor
Write Markdown with a live preview, formatting toolbar and one-click export. Auto-saves.
Fake / Test Data Generator
Build a schema and generate realistic mock data in bulk — export JSON, NDJSON, CSV or SQL. Seeded for reproducible fixtures, 100% private.
Developer Tools — frequently asked questions
Yes. Everything is processed locally in your browser — JWTs, hashes, JSON and regex input are never transmitted, logged or stored, so real secrets and proprietary code stay on your machine.
They follow the standards: PCRE-style regex semantics, standard cron syntax with next-run previews, RFC-compliant JWT decoding, exact CIDR maths and WCAG 2.x contrast ratios — so results transfer directly to your codebase.
Yes — output from the fake-data generator and JSON-to-code tool is yours to use freely in personal and commercial projects, with deterministic seeds so fixtures are reproducible in CI.
Explore more free tools
Every category, every tool — free, no sign-up.
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