10 Essential Free Developer Tools
Every developer has a private toolbox of little web utilities. The catch: pasting API payloads and tokens into random websites is a security habit nobody should have. All ten tools below process everything locally in your browser — nothing you paste is ever transmitted.
1. JSON Formatter — the daily driver
Minified API responses become readable in one paste with the JSON Formatter — pretty-print, minify and validation with a clear error message pointing at the broken line.
2. Regex Tester — see matches as you type
The Regex Tester highlights matches and capture groups live against your own sample text — the fastest way to debug a pattern before it ships inside a validation rule.
3. JWT Decoder — look inside your tokens
The JWT Decoder splits a token into header and payload and shows the claims — expiry, issuer, scopes — locally, which is exactly where you want auth tokens decoded.
4. Base64 Encode/Decode — the plumbing format
Auth headers, data URIs, config blobs: the Base64 tool converts both directions instantly, and the Base64 to Image decoder handles embedded images.
5. YAML ↔ JSON — config file translator
Kubernetes manifests, CI configs and OpenAPI specs live in YAML; APIs speak JSON. The YAML to JSON convertertranslates both ways and shows exactly how the parser interpreted your indentation — the quickest debugger for “valid but wrong” configs.
6. XML Formatter — for the enterprise formats
SOAP payloads, RSS feeds and Maven files still arrive minified. The XML Formattervalidates with the browser's native parser and pretty-prints with your indent choice.
7. Cron Expression Parser — schedule with confidence
The Cron Parsertranslates five-field expressions into plain English and lists the next five run times — ending the “will this fire at midnight or noon?” guessing game.
8. UUID Generator — unique IDs on demand
The UUID Generatorproduces v4 UUIDs with the browser's crypto API — test fixtures, database seeds, one-off identifiers.
9. Epoch Converter — timestamps to human time
The Epoch Converter turns Unix timestamps into readable dates and back, auto-detecting seconds vs milliseconds — the eternal log-file companion.
10. Text Diff Checker — what actually changed?
Two config versions, two API responses: the Diff Checker highlights line-level differences instantly, no git required.
The security angle
Tokens, payloads and configs are exactly the data that shouldn't travel to unknown servers. Every tool above runs client-side — open the network tab and watch: no requests carry your input anywhere. Bookmark the ones you use; they also keep working offline once loaded.