DevToolz - Fast & Private Online Developer Tools & AI Utilities

A suite of 28+ free, fast, and privacy-focused online developer tools running 100% in your browser. JSON formatters, JWT decoders, UUID generators, and LLM prompt engineering utilities.

Developer Tools Directory

JSON Formatter & Validator - Format and Validate JSON Online: Free online JSON Formatter and Validator. Beautify minified JSON, fix syntax errors with exact line pointers, and inspect API responses securely in your browser.
Base64 Encoder / Decoder - Free Online Base64 Tool: Convert text, images, and binary data to Base64 format or decode Base64 strings back to original text. Supports URL-safe Base64 and UTF-8 encoding.
URL Encoder / Decoder - Free Online Percent-Encoding Tool: Safely encode special characters into percent-encoded (%XX) format or decode encoded URLs back to human-readable strings. Supports RFC 3986 standards.
JSON to TypeScript Converter - Generate TS Interfaces Instantly: Instantly convert raw JSON payloads into clean, type-safe TypeScript interfaces and types. Supports nested objects, optional fields, and array item typing.
JSON Schema Generator - Online JSON to Schema Converter: Generate standard JSON Schema specifications (Draft-07 / Draft-2020-12) from sample JSON payloads. Perfect for API validation and OpenAPI/Swagger documentation.
JWT Decoder - Decode & Inspect JSON Web Tokens Online: Securely decode and inspect JSON Web Tokens (JWT) in your browser. View Header algorithms, Payload claims, and expiration timestamps without sending your token to any server.
Password Generator - Strong & Secure Random Password Generator: Generate strong, unpredictable random passwords with customizable length, numbers, symbols, and ambiguous character filters using cryptographic entropy.
Hash Generator - MD5, SHA-1, SHA-256, SHA-512 Online: Calculate cryptographic hash checksums including MD5, SHA-1, SHA-256, and SHA-512 in real time. Perfect for data integrity verification, password digests, and commit hashing.
UUID Generator - Generate RFC 4122 v4 UUIDs Online: Generate cryptographically random UUID v4 (Universally Unique Identifiers) instantly. Supports batch generation, hyphen toggling, uppercase/lowercase formatting, and JSON export.
Diff Checker - Compare Text, Code & JSON Differences Online: Compare two text files, code snippets, or JSON documents side-by-side or in unified inline view. Highlights added, removed, and modified lines with precision.
Regex Tester - Regular Expression Tester & Debugger: Test and debug regular expressions with real-time match highlighting, capture group extraction, and flag toggles (g, i, m, s). Includes a cheat sheet for common regex patterns.
Unix Timestamp Converter - Epoch Seconds & Milliseconds to Date: Convert Unix epoch timestamps (seconds and milliseconds) to human-readable UTC and local date-time strings, or convert calendar dates back to Unix timestamps in real time.
Text Analyzer - Word Count, Character Count & Read Time Tool: Analyze character count (with/without spaces), word count, UTF-8 byte size, reading time, and keyword frequency in real time. Ideal for blog posts, SEO metadata, and DB string limit checks.
Markdown Editor - Free Online Markdown Editor & Live Preview: Write and preview GitHub Flavored Markdown (GFM) with live split-screen rendering, syntax highlighting, table generation, and one-click HTML / Markdown export.
Color Converter - HEX, RGB, HSL, CMYK Online Color Tool: Convert colors seamlessly across HEX, RGB, HSL, and CMYK formats with real-time visual picker, WCAG contrast ratio analysis, and CSS code copy.
QR Code Generator - Custom QR Codes with Colors & Download: Generate high-resolution QR codes for URLs, Wi-Fi networks, text, and contact cards. Customize foreground/background colors, error correction levels, and download in PNG or SVG.
Image Compressor - Compress PNG, JPEG & WebP Online Free: Compress JPEG, PNG, and WebP images up to 80% without noticeable quality loss. Operates completely in your browser memory for total privacy.
LLM Token Counter - Calculate Tokens for GPT-4o, Claude & Gemini: Calculate exact token counts and estimated API inference costs across OpenAI GPT-4o, Anthropic Claude 3.5, and Google Gemini models in real time.
LLM Context Optimizer - Package Files & Code for AI Prompts: Format multiple source files, directory structures, and system instructions into a single token-efficient Markdown prompt ready for ChatGPT, Claude, and Gemini.
Prompt Wrapper - XML Tag & Role-Based Prompt Structuring: Wrap and structure raw instructions into high-performing XML tags (, , ) following Anthropic Claude and OpenAI best practices.
RAG Chunking Simulator - Visualize Vector Search Chunk Splits: Simulate and visualize text chunking strategies for Retrieval-Augmented Generation (RAG). Experiment with character vs token chunk sizes, overlap percentages, and recursive splitters.
System Prompt Generator - Production System Prompts for AI: Craft battle-tested system prompts with strict personas, tone guidelines, JSON output constraints, and negative prompt safeguards for OpenAI, Anthropic, and Gemini.
Prompt Variable Injector - Dynamic Template Interpolator: Interpolate dynamic variables like {{username}} or {{context}} into prompt templates with real-time preview, multiple variable datasets, and batch prompt generation.
Prompt Token Splitter - Split Long Texts for LLM Context Limits: Divide massive books, logs, and codebases into sequential token-safe prompts with continuum headers, part counters (Part 1 of N), and overlap to prevent truncation.
LLM Parameter Playground - Simulate Temperature, Top-P & Penalties: Interactive visual simulator for LLM generation parameters: Temperature, Top-P (nucleus sampling), Top-K, and Frequency/Presence penalties. Master probability distributions.
XML Guardrail Generator - AI Safety & Anti-Hallucination Rules: Generate production-grade safety guardrails, refusal triggers, and anti-hallucination XML rules (, ) for enterprise LLM deployments.
Few-Shot Prompt Builder - Input/Output Example Pair Structuring: Build and format high-performing Few-Shot example pairs (Input / Output) for LLM prompts. Supports edge cases, XML encapsulation, JSON formatting, and negative demonstrations.
Function Calling Builder - OpenAI & Anthropic Tool Definition Tool: Visually define function parameters, descriptions, and JSON Schemas to generate standard "tools" payload configurations for OpenAI, Anthropic Claude, and Gemini API calls.