Online tools
Free online developer tools and calculators
A curated collection of fast browser-based tools for developers, makers and everyday calculations. Format JSON, decode JWTs, convert Unix timestamps, encode Base64, generate UUIDs, estimate LLM tokens, calculate percentages, VAT, margins, markup and more.
Developer tools
Fast browser-based utilities for API debugging, encoded data, JSON payloads, authentication tokens and AI workflows.
JSON Formatter and Validator
Format, validate and minify JSON directly in your browser. Useful for API responses, payloads and config files.
JWT Decoder
Decode JSON Web Tokens and inspect header, payload, claims, expiration time and signature.
Base64 Encoder and Decoder
Encode text to Base64 or decode Base64 strings for API payloads, tokens and debugging.
Unix Timestamp Converter
Convert Unix timestamps and epoch time to readable dates, or convert dates back to timestamps.
URL Encoder and Decoder
Encode and decode URLs for query strings, redirects, callback URLs and API parameters.
UUID Generator
Generate UUID v4 identifiers for APIs, databases, test fixtures and software development.
LLM Token Estimator
Estimate token usage and approximate cost for prompts, JSON payloads and AI workflows.
Business calculators
Simple calculators for prices, discounts, profit, margins, markup and salary estimates.
Percentage Calculator
Calculate percentages, discounts, increases, reductions and percentage ratios instantly.
VAT Calculator
Add or remove VAT at 22%, 10% or 4% and get net, VAT and gross amounts.
Margin Calculator
Calculate profit margin from cost and selling price or find a price from a target margin.
Markup Calculator
Calculate markup from cost and selling price or find a selling price from a target markup.
Inverse Discount Calculator
Find the original price from a discounted price and discount percentage.
Net Salary Calculator
Estimate monthly take-home pay and annual net salary from gross annual income.
Unit conversions
Quick conversions for common units used in everyday calculations, technical work and international references.
Browser-based and privacy-friendly
Most tools run directly in your browser, which makes them fast and practical for quick checks, debugging sessions and everyday calculations. Tools that handle sensitive text, such as JWT, JSON, Base64 and token estimation, are designed to work without sending your input to external servers.