PocketKit
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.
Start here
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
AI Prompt & System Prompt Generator
Structure and optimize system prompts for DeepSeek, Claude, and ChatGPT with code review, translation and content templates
Keep exploring
More tools (34)
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
Multimodal Vision Token Counter
Calculate image tile vision tokens and API cost for GPT-4o, Claude 3.5 Sonnet and Gemini 1.5
System Prompt Anti-Leak & Jailbreak Auditor
Audit system prompt robustness against 20+ LLM injection patterns and auto-patch structural directives
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
Decision guide
Development and debugging matrix
| Input | What it does | What it does not prove |
|---|---|---|
| JSON | Formatting, syntax validation and structure review | JSON Formatter |
| JWT | Read header and payload | JWT Parser |
| Base64 | Encode and decode byte representation | Base64 Encode/Decode |
| Cron | Generate and explain schedules | Cron Generator |
FAQ
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.