Top 15 Free Developer Tools You Should Bookmark

Every developer has a "tools" bookmark folder — JSON formatter, regex tester, base64 decoder, JWT inspector. Most are slow, ad-laden, or trying to upsell you. Here are 15 free, instant-loading tools you should actually bookmark in 2026, organised by category.

JSON tools

1. JSON Formatter & Beautifier

Pretty-print JSON, validate it, syntax-highlight, fold sections. fmt.hjlabs.in/json-formatter — runs 100% in the browser, no upload, handles 10MB+ files.

2. JSON Validator

Detailed error messages with line numbers. fmt.hjlabs.in/json-validator.

3. JSON Minifier

Strip whitespace for production payloads. fmt.hjlabs.in/json-minify.

4. JSON to CSV

Convert nested JSON arrays to CSV with auto-flattening. fmt.hjlabs.in/json-to-csv.

5. JSON to YAML

Quick conversion for Kubernetes configs and CI/CD pipelines. fmt.hjlabs.in/json-to-yaml.

Encoding tools

6. Base64 Encoder/Decoder

Encode/decode Base64 (standard and URL-safe). fmt.hjlabs.in/base64.

7. URL Encoder/Decoder

Percent-encode and decode URL components. fmt.hjlabs.in/url-encode.

Auth and crypto

8. JWT Decoder

Decode JWT tokens — view header, payload, expiry. Verify signature structure. fmt.hjlabs.in/jwt-decoder. The most-used tool in the suite.

9. Hash Generator

Generate MD5, SHA-1, SHA-256, SHA-512 hashes. fmt.hjlabs.in/hash-generator.

IDs and time

10. UUID Generator

Generate UUID v4 (random) and v7 (time-ordered). Bulk generate up to 1000 at a time. fmt.hjlabs.in/uuid-generator.

11. Unix Timestamp Converter

Convert between Unix seconds, milliseconds, and human-readable dates. Multiple timezone display. fmt.hjlabs.in/timestamp.

Text and code

12. Diff Checker

Compare two texts side-by-side or inline. Word-level highlighting within changes. fmt.hjlabs.in/diff.

13. Regex Tester

Test regular expressions with real-time matching. Capture groups highlighted. fmt.hjlabs.in/regex.

Visual content

14. OG Image Generator

Generate 1200x630 social preview images via URL. 6 templates. og.hjlabs.in/og-image-generator.

15. Favicon Generator

Generate favicons in every size (16, 32, 48, 64, 128, 180, 192, 512) plus PWA manifest. From text, emoji, or upload. og.hjlabs.in/favicon-generator.

Why these specifically

The criteria for inclusion:

1. Loads in <500ms — no spinners, no progress bars
2. Runs in the browser — your data never leaves your machine (sensitive JSON, JWTs, etc.)
3. No signup, no login, no rate limits for casual use
4. No tracking pixels or third-party ads
5. Mobile-friendly — useful on phones during incident response
6. Open source — verifiable on GitHub

Honourable mentions (not in the 15)

• JSONHero — tree-view JSON browser, useful for very large files
• Beautifier.io — code beautifier for many languages
• RegEx101 — regex with explanation pane (heavier but excellent)
• JWT.io — historical JWT decoder, still useful
• Excalidraw — quick architecture sketches
• cron.help — cron expression explainer
• tldraw — open-source whiteboard
• tldp.org — old-school Linux docs, still good

How to bookmark efficiently

Two options:

1. Browser bookmark folder named "Dev Tools" with all 15 — slow to navigate
2. Bookmark just fmt.hjlabs.in — landing page lists all tools with search. One bookmark, instant access.

Self-hosting

The entire fmt.hjlabs.in suite is open source on GitHub. Deploy your own Cloudflare Worker in 5 minutes if you want full control or want to keep the tools available offline behind your VPN.

What's not on this list (deliberately)

• "Free" tools that ask for email after one use. Friction kills the daily-driver value.
• Tools that send your data to a server. If you paste a JWT or API response, you don't want it logged anywhere.
• Tools with crypto/wallet upsells. Hard pass.
• Tools without HTTPS. Reject on principle.

Bottom line

Bookmark fmt.hjlabs.in and og.hjlabs.in. Between them, you cover ~95% of the everyday "I need to format/decode/generate this" tasks. All free, all instant, all browser-side, all open source.