Free online developer tools
Use free JSON, JWT, regex, code-formatting, encoding and API utilities in your browser. Ready to use with no installation or account required.
What can you do with these tools?
Developer utilities support debugging, API work and everyday text processing, including JSON validation, JWT inspection, regex testing, code formatting, command conversion and configuration generation. Input is generally processed in the browser; DNS, network and live-data tools clearly disclose network activity.
Core tools
- JSON Formatter — Format, minify and validate JSON
- JWT Parser — Decode and parse JWT tokens offline
- Regex Tester — Test regex matches and groups live
- Code Formatter — Beautify JS / JSON / CSS / HTML
- cURL to Code — Convert a curl command into JS fetch / axios / Python requests / Go code, detecting method, headers and JSON body
- Cron Generator — Generate and parse Cron expressions with execution schedule preview
- Base64 Encode/Decode — Convert text to/from Base64
- URL Encode/Decode — Encode / decode URL components
Development and debugging matrix
| Task or input | Tool | Decision criteria and limits |
|---|---|---|
| JSON | JSON Formatter | Valid syntax does not prove schema compliance |
| JWT | JWT Parser | Reading payload does not verify signature or issuer |
| Base64 | Base64 Encode/Decode | Encoding byte representation is not encryption |
| Cron | Cron Generator | Test timezone and boundaries in the runtime |
Recommended workflow
- Remove secrets, tokens and personal information
- Format or decode to locate the issue
- Test signatures, permissions and boundaries in production-like conditions
More tools (33)
- AI Prompt & System Prompt Generator — Structure and optimize system prompts for DeepSeek, Claude, and ChatGPT with code review, translation and content templates
- Claude Env Scanner & Region Checker — Check browser timezone, system locale, language, and font fingerprints to detect Claude region blocking or account ban risks, helping you secure proxy configurations.
- Claude Proxy Network Checker (Exit IP & Timezone) — Detect your real exit IP and region, cross-check it against system timezone, language and WebRTC leaks to find proxy exposure points and reduce Claude ban risk
- AI Token Counter & Cost Estimator — Estimate token counts locally and compare API costs across Claude, GPT, Gemini and DeepSeek models
- LLM API Pricing Comparison — Compare input/output/cached prices, context windows and blended cost across Claude, GPT, Gemini and DeepSeek
- Tool & Function Schema Converter — Convert between Claude tool, OpenAI function, Gemini functionDeclaration and JSON Schema — with strict mode
- Keycode Info — Get keyboard event key, code, and keycode details
- User Agent Parser — Parse User Agent strings to identify browser, OS, and device
- Bcrypt Generator — Generate and verify Bcrypt password hashes
- HMAC Generator — Compute HMAC signatures (SHA256/512) for messages
- IPv4 Subnet Calculator — Compute subnet mask, network range, usable IPs and binary format
- Docker Compose Converter — Convert docker run commands to docker-compose.yml format
- Chmod Calculator — Calculate Linux file/directory permission values and command
- BIP39 Generator — Generate and verify multi-language BIP39 mnemonic phrases
- ULID Generator — Generate lexicographically sortable unique identifiers
- URL Parser — Parse URL structures and edit query parameters interactively
- Timestamp Converter — Convert between Unix time and dates
- Base Converter — Convert between 2/8/10/16
- ASCII Table — Look up ASCII 0-127
- HTTP Status Codes — Common status codes reference
- Password Generator — Generate secure random passwords
- Docker Command — Build a docker run command
- Windows Commands — Generate common Windows commands
- Linux Commands — Generate common Linux commands
- UUID Generator — Generate UUID v4 in bulk
- Hash — MD5 / SHA-1 / SHA-256…
- AES Encrypt — AES-256-GCM with password
- RSA — Generate keypair, encrypt/decrypt
- MIME Types — Extension ⇄ MIME lookup
- UCharts Builder — Create beautiful interactive charts from raw data grids locally
- SQL Formatter — Beautify SQL by breaking and indenting at major clauses and normalizing keyword case
- JSON to Types — Infer TypeScript interfaces, Go structs or Python TypedDict from JSON, with nested types and array merging
- GPT Token Counter — Count GPT-4o/4/3.5 tokens exactly with OpenAI's official BPE (o200k/cl100k) locally and estimate cost
Frequently asked questions
Can I paste sensitive JSON or JWT data?
Input is generally processed in the browser, but JWT payloads can contain private data. Remove secrets, tokens and personal information first, and use a trusted device and browser environment.
Does decoding a JWT verify its signature?
No. Reading the header and payload only decodes content. Trust requires signature, expiry and issuer validation with the correct key.
Can developer tools work offline?
Many text and format utilities can keep working after their resources load, while DNS, network diagnostics and live-data queries still require a connection.