Every developer's browser bookmarks hide a pile of "dev tool" links. This article covers the 10 most frequently used categories: what they solve, how they work, common pitfalls, and when to use a browser tool vs the command line.
⚠️ Security Note
Developer tools often handle sensitive data: JWTs contain identity, JSON contains API keys. Prefer browser-local tools or IDE plugins.
1. JSON Format & Validate
Mechanism: JSON.parse() + JSON.stringify(obj,null,2). Pitfalls: JSON has no comments, no trailing commas, no single quotes; keys must be double-quoted.
👉 JSON Formatter
2. JWT Decode
JWT structure: header.payload.signature. First two parts are Base64URL-encoded JSON. Critical: JWT payload is NOT encrypted — anyone can decode it. Don't paste production JWTs into cloud tools.
👉 JWT Decoder
3. Regex Tester
Uses RegExp + matchAll. Pitfalls: regex dialects differ across languages; greedy vs non-greedy; (a+)+b nested quantifiers cause exponential backtracking.
👉 Regex Tester
4. Base64 Encode/Decode
Every 3 bytes → 4 six-bit units. Variants: standard, URL-safe, Base64URL (no padding, used by JWT).
👉 Base64 Tool
5. UUID Generator
- v4: pure random, most common;
- v7: 2022 version, timestamp prefix, sortable, ideal for DB primary keys.
👉 UUID Tool
6. Timestamp Conversion
Must know: JS Date.now() returns ms, PHP/Python time() returns sec; UTC vs local; Year 2038 problem.
👉 Timestamp Tool
7. Hash (MD5 / SHA)
Misuse: MD5/SHA-1 can't store passwords (use bcrypt/argon2); MD5 collisions are broken — use SHA-256+ for signatures.
👉 Hash Tool
🛠️
See all 30 tools
PDF, Excel, images, dev tools — all local processing
→
8. URL Encode/Decode
encodeURI vs encodeURIComponent: always use the latter for query params. + trap: + means space in URL query strings.
👉 URL Tool
9. QR Code Generation
See dedicated post: Complete QR Code Guide.
👉 QR Tool
10. Text Diff
Core algorithm: Myers' or Patience diff. Tip: IDE diff is easiest for code; format JSON first before diffing.
👉 Text Diff Tool
When NOT to Use Online Tools
- Production sensitive data → IDE plugin;
- Automation pipelines → CLI;
- Large file batches → CLI;
- Need history → IDE / dedicated app.
Conclusion
These 10 tools cover ~80% of developers' "small task" scenarios. Bookmark them, but also learn the CLI equivalents.