Developer Tools
Handy utilities for developers building with AI APIs. Everything runs in your browser — nothing leaves your device.
Token Counter
Count tokens in your prompt or document and see estimated API cost for GPT-4o, Claude, Gemini, and more. Also shows context window usage.
Context Window Checker
Paste any document to instantly see which LLMs can handle it. Visual progress bars across GPT-4o, Claude, Gemini 1.5 Pro, Llama, and more.
JSON Formatter & Validator
Prettify, minify, validate, or escape JSON for AI prompts — entirely in your browser. Syntax-highlighted output, no data uploaded.
Prompt Diff Tool
Compare two prompts or AI outputs side-by-side with word-level highlighting. Perfect for A/B testing prompt versions and reviewing LLM changes.
Audio to Base64 Converter
Encode MP3, WAV, FLAC, OGG, M4A and other audio files to base64 for Sarvam STT, Whisper, and other AI speech APIs. Preview audio in-browser before copying. Also decodes base64 back to audio.
Base64 to Image Converter
Paste a base64 string and instantly preview the image in your browser. Supports PNG, JPEG, WebP, GIF, SVG. Also encodes local images to base64.
PDF to Base64 Converter
Encode any PDF to base64 to use with Claude, Gemini, or other document AI APIs. Includes a ready-to-use Python snippet. Also decodes base64 back to a downloadable PDF.
System Prompt Library
Browse hundreds of curated system prompts across coding, writing, customer service, education, and more. Maintained by masterprompting.net.
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