Free Online Developer Tools

A developer toolbox for the small jobs between commits: format and validate JSON, test a regular expression, decode and verify a JWT, convert epoch timestamps, build a cron schedule, decode an SSL certificate, split a subnet, or fire an HTTP request and copy it as cURL.

Tokens, certificates and databases are parsed locally in the browser tab. The SQLite sandbox opens your .db file in memory, the JWT decoder verifies signatures without sending the token anywhere, and the API tester calls your endpoint directly from the browser with no proxy in between. Nothing here needs an account, so the tools work behind a VPN or on a locked-down laptop.

• JSON Formatter & Type Generator — Format, minify, and generate types from JSON payloads up to 100MB+, no freeze.
• RegEx Visualizer & Builder — Build and test regular expressions safely with a ReDoS watchdog and railroad diagrams.
• SQL Sandbox — Run queries and view a schema ERD against a local SQLite file, zero upload.
• Cron Expression Builder — Build or explain UNIX, Quartz, and AWS EventBridge cron expressions in plain English.
• JWT Decoder — Decode and optionally verify a JWT's header, payload, and signature — never transmitted.
• Epoch / Unix Timestamp Converter — Convert between a Unix timestamp and a human-readable date, either direction.
• SSL/TLS Certificate Decoder — Inspect a PEM/DER certificate's subject, issuer, validity, SANs, signature algorithm, and fingerprint entirely client-side.
• Subnet/CIDR Calculator — Compute network address, broadcast address, usable host range, and subnet mask for any IPv4 or IPv6 CIDR block.
• Enterprise Password Policy & Hash Entropy Tester — Model a corporate password policy against real-world crack-time and entropy estimates.
• File Extension Sorter — Drop in a folder or zipped repo and get back a ZIP organized into one folder per file extension.
• API Request Builder & Tester — Build HTTP requests, inspect timing, headers, and responses, and copy cURL without sending request data through BrakeTools.

Other categories: Documents · Media · Hardware · Finance · Workspace · Generators · Calculators · Cloud · Business · Cryptography