Free online tools for developers, engineers & students

Format JSON, merge PDFs, remove image backgrounds, test regex, query CSV with SQL, and learn with interactive engineering and AI visualisers. 8 categories, all free and private.

A good place to start.

JSON Formatter

Format, validate and beautify JSON data with tree view and syntax highlighting.

PDF Toolkit

Merge, split, extract, remove, and rotate PDF pages - 100% in your browser, no upload required.

AI Background Remover

Remove image backgrounds with on-device AI. Photos never leave your browser - export transparent PNGs.

Regex Tester

Test and debug regular expressions with real-time matching, groups, and flags.

Base64 Encoder / Decoder

Encode and decode text or files to and from Base64 format.

QR & Barcode Generator

Generate QR codes and barcodes from text, URLs, or data.

Mermaid Diagram Editor

Write Mermaid, then drag shapes into place and recolour any node or link. Export PNG, JPG, or SVG at up to 4x.

SQL Playground

Run real SQLite queries on CSV files in your browser. Import, join, aggregate, and export results.

Text & Code

Format, compare and clean up text and code.

JSON Formatter

Format, validate and beautify JSON data with tree view and syntax highlighting.

Regex Tester

Test and debug regular expressions with real-time matching, groups, and flags.

Markdown Preview

Write Markdown and preview the rendered HTML output in real time.

Text Diff

Compare two blocks of text side by side and highlight the differences.

Lorem Ipsum Generator

Generate placeholder text in paragraphs, sentences, or words for designs and mockups.

Code Minifier

Minify HTML, CSS, and JavaScript code to reduce file size.

Slug Generator

Convert any text into a URL-friendly slug for SEO-optimized links.

Word Counter

Count words, characters, sentences, and paragraphs with reading time estimate.

Encoding & Data

Encode, decode, hash and convert data formats.

Base64 Encoder / Decoder

Encode and decode text or files to and from Base64 format.

URL Encoder / Decoder

Encode and decode URL components for safe use in query strings.

HTML Entity Encoder

Encode and decode HTML entities like &, <, > and more.

JWT Decoder

Decode and inspect JSON Web Tokens (JWT) header and payload.

Hash Generator

Generate MD5, SHA-1, SHA-256, SHA-512 and other cryptographic hashes.

CSV / JSON Converter

Convert between CSV and JSON formats easily.

Number Base Converter

Convert numbers between binary, octal, decimal, and hexadecimal bases.

Developer Utilities

Config builders, converters and API helpers.

XML ↔ JSON Converter

Translate between XML and JSON data structures with support for attributes.

YAML ↔ JSON Converter

Convert between YAML and JSON formats - essential for DevOps and config files.

cURL to Fetch/Axios

Paste a cURL command and get JavaScript fetch() or Axios code.

Postman to cURL

Convert Postman collection JSON into cURL commands for each endpoint.

JSON Schema Validator

Validate JSON data against a JSON Schema definition with detailed errors.

SQL Query Beautifier

Format minified SQL queries into readable, properly indented text.

Git Command Generator

Visual UI to build complex Git commands - rebase, cherry-pick, reset, and more.

Dockerfile Generator

Interactive UI to create optimized Dockerfiles for Node, Python, Go, and more.

Nginx / Apache Config

Visual builder for server routing, SSL, caching, and security rules.

SemVer Calculator

Calculate and manage semantic version number increments and comparisons.

Event Keycode Finder

Press any key to see its event.keyCode, event.key, and event.code.

Mock Data Generator

Generate massive JSON arrays of fake names, emails, addresses, and more.

Bencode Decoder

Decode Bencode data and torrent file metadata into readable JSON.

MIME Type Lookup

Search by file extension to find the correct MIME type.

Mermaid Diagram Editor

Write Mermaid, then drag shapes into place and recolour any node or link. Export PNG, JPG, or SVG at up to 4x.

Pseudocode Builder

Visual drag-and-drop pseudo-code flow builder with logic blocks, templates, animated execution engine, and JSON export.

Web & Design

Colors, CSS, images, favicons and meta tags.

QR & Barcode Generator

Generate QR codes and barcodes from text, URLs, or data.

Color Converter

Convert colors between HEX, RGB, HSL, and other color formats.

CSS Gradient Generator

Create beautiful CSS gradients with a visual editor and copy the code.

Box Shadow Generator

Design CSS box shadows visually and export the CSS code.

Image Resizer

Resize, crop, and optimize images right in your browser.

SVG Previewer

Preview and inspect SVG code with live rendering.

Favicon Generator

Generate favicons in multiple sizes from an image or emoji.

Meta Tag Generator

Generate Open Graph, Twitter Card, and standard HTML meta tags.

Aspect Ratio Calculator

Calculate and convert aspect ratios for images and video.

Files & Media

PDFs, images and CSV files, processed locally.

PDF Toolkit

Merge, split, extract, remove, and rotate PDF pages - 100% in your browser, no upload required.

AI Background Remover

Remove image backgrounds with on-device AI. Photos never leave your browser - export transparent PNGs.

SQL Playground

Run real SQLite queries on CSV files in your browser. Import, join, aggregate, and export results.

Utilities

UUIDs, passwords, timestamps, cron and networks.

UUID Generator

Generate unique UUIDs (v4) for use in databases and applications.

Password Generator

Generate strong, secure passwords with customizable options.

Unix Timestamp Converter

Convert between Unix timestamps and human-readable dates.

Cron Expression Generator

Build and validate cron expressions with a visual editor.

Chmod Calculator

Calculate Unix file permissions in numeric and symbolic notation.

IP / Subnet Calculator

Calculate subnet masks, network ranges, and CIDR notation.

Learning Tools

Interactive engineering, AI and math calculators.

Engineering

Engineering Unit Converter

Convert length, mass, pressure, energy, power, force, temperature and more across SI and imperial units.

Resistor Color Code Calculator

Decode 4, 5, and 6-band resistor colors to resistance, tolerance, and temperature coefficient.

Ohm's Law Calculator

Enter any two of voltage, current, resistance, or power - solve the other two instantly.

555 Timer & RC Filter Designer

555 astable/monostable timing plus RC filter cutoff frequencies with response plots.

Beam Calculator

Live shear force, bending moment, and deflection diagrams for simply-supported and cantilever beams.

Bode Plot Generator

Enter a transfer function H(s) and get magnitude and phase Bode plots instantly.

Gear Ratio Calculator

Gear ratios, output speed, and torque with an animated gear pair.

Wire Gauge (AWG) Calculator

Pick the right copper wire size from current, run length, and allowed voltage drop.

AI & Machine Learning

LLM Tokenizer Playground

See how language models split text into tokens - counts, token IDs, and API cost estimates.

Neural Network Playground

Train a real neural network in your browser and watch the decision boundary learn.

Activation Function Visualizer

Compare ReLU, GELU, sigmoid, tanh, Swish and their derivatives interactively.

Confusion Matrix Calculator

Precision, recall, F1, specificity, and MCC from a matrix or pasted predictions.

Gradient Descent Visualizer

Watch SGD, Momentum, and Adam race across loss surfaces - click to drop optimizers anywhere.

Physics & Math

Function Grapher

Plot functions, overlay derivatives, and find roots - a lightweight graphing calculator.

Matrix Calculator

Determinant, inverse, RREF, rank, eigenvalues, transpose, and matrix multiplication.

Projectile Motion Simulator

Animated trajectories with launch angle, height, and air resistance - plus live stats.

Significant Figures Calculator

Count sig figs, do sig-fig-correct arithmetic, and propagate measurement uncertainties.

Wave Interference Visualizer

Superpose two waves in real time - beats, phase interference, and standing waves.

Statistics Calculator

Descriptive stats, histogram, and t-tests (one-sample and Welch) from pasted data.

LaTeX Equation Editor

Write LaTeX math with instant KaTeX preview, snippets, and copy-ready output formats.

Science

Chemistry and science visualisers.

Scientific Visualizer

Drag & drop periodic table elements onto a zoomable canvas. Build compounds, calculate molecular formulas, save templates, and export as JSON/SVG/PNG.

Why use these tools

Private by design

Nothing you paste or upload leaves your browser.

Instant

No accounts, no waiting, no install. Open a tool and use it.

Works everywhere

Responsive layouts with dark and light themes.

Built for learning

Interactive visualisers for engineering, AI and math.

Frequently asked questions

Are these tools really free?

Yes. Every tool is free with no signup, no usage limits and no premium tier.

Is my data uploaded anywhere?

No. The tools run entirely in your browser with JavaScript. Files you open, text you paste and images you process stay on your device and are never sent to a server.

Do the tools work on mobile?

Yes. Every page is responsive and works in any modern browser on phones, tablets and desktops. A few heavier tools, such as the AI background remover, run faster on a desktop.

Which tools are good for students?

The Learning Tools section has interactive calculators for engineering (beam, Bode plot, resistor, Ohm's law), AI and machine learning (neural network playground, tokenizer, gradient descent) and physics and math (matrix calculator, function grapher, statistics, LaTeX editor).

Can I suggest a new tool?

Yes. Get in touch through the contact section on vidu.dev and describe what you need.