Free online developer tools

123024.com offers 60+ privacy-first developer tools. Everything runs locally in your browser — nothing is uploaded.

Encoding & Decoding

Base64 — Base64 — runs entirely in your browser; nothing is uploaded.
URL — URL — runs entirely in your browser; nothing is uploaded.
JWT — JWT — runs entirely in your browser; nothing is uploaded.
UTF-8 — UTF-8 — runs entirely in your browser; nothing is uploaded.
ASCII / Native — ASCII / Native — runs entirely in your browser; nothing is uploaded.
Hex — Hex — runs entirely in your browser; nothing is uploaded.
HTML — HTML — runs entirely in your browser; nothing is uploaded.
Unicode — Unicode — runs entirely in your browser; nothing is uploaded.

Format & Convert

JSON — JSON — runs entirely in your browser; nothing is uploaded.
YAML ↔ JSON — YAML ↔ JSON — runs entirely in your browser; nothing is uploaded.
JSON ↔ CSV — JSON ↔ CSV — runs entirely in your browser; nothing is uploaded.
JSON → Class — Generate TypeScript, Java, Go, Rust, or C++ classes and structs from JSON — entirely in your browser.
SQL Formatter — SQL Formatter — runs entirely in your browser; nothing is uploaded.
Base Convert — Base Convert — runs entirely in your browser; nothing is uploaded.
Color Converter — Color Converter — runs entirely in your browser; nothing is uploaded.
CSS Unit Converter — CSS Unit Converter — runs entirely in your browser; nothing is uploaded.
Case Converter — Case Converter — runs entirely in your browser; nothing is uploaded.

Crypto & Security

Hash — Hash — runs entirely in your browser; nothing is uploaded.
HMAC — HMAC — runs entirely in your browser; nothing is uploaded.
AES Encrypt/Decrypt — AES Encrypt/Decrypt — runs entirely in your browser; nothing is uploaded.
RSA Encrypt/Decrypt — RSA Encrypt/Decrypt — runs entirely in your browser; nothing is uploaded.
Password Generator — Password Generator — runs entirely in your browser; nothing is uploaded.
UUID Generator — UUID Generator — runs entirely in your browser; nothing is uploaded.
TOTP / 2FA — TOTP / 2FA — runs entirely in your browser; nothing is uploaded.
SM3 Digest — SM3 Digest — runs entirely in your browser; nothing is uploaded.
SM4 Symmetric — SM4 Symmetric — runs entirely in your browser; nothing is uploaded.
SM2 Asymmetric — SM2 Asymmetric — runs entirely in your browser; nothing is uploaded.
SSL Certificate Checker — SSL Certificate Checker — runs entirely in your browser; nothing is uploaded.
File Checksum — File Checksum — runs entirely in your browser; nothing is uploaded.

Generators

Unix Timestamp — Unix Timestamp — runs entirely in your browser; nothing is uploaded.
QR Code Generator — QR Code Generator — runs entirely in your browser; nothing is uploaded.
Cron Expression Builder — Cron Expression Builder — runs entirely in your browser; nothing is uploaded.
Lorem Ipsum — Generate placeholder text for design and layout — runs entirely in your browser; nothing is uploaded.
Mock Data Generator — Generate mock names, emails, phones, and addresses — runs entirely in your browser; nothing is uploaded.

Reference & Lookup

HTTP Status Codes — HTTP Status Codes — runs entirely in your browser; nothing is uploaded.
ASCII Table — ASCII Table — runs entirely in your browser; nothing is uploaded.
HTML Entity Reference — HTML Entity Reference — runs entirely in your browser; nothing is uploaded.

Text Processing

Regex Tester — Test regular expressions in real-time with match highlighting, capture group inspection, and replacement preview. Built-in preset library and token-level explanation.
Text Diff — Compare two texts with line and word-level precision. Side-by-side or inline view with collapsible unchanged regions.
Word / Character Counter — Count words, characters, sentences, and paragraphs; estimate reading and speaking time; analyze keyword density. Runs entirely in your browser.
Markdown Preview — Write and preview Markdown with GFM, syntax highlighting, Mermaid diagrams, and PDF/PNG export. Runs entirely in your browser.
cURL → Code — cURL → Code — runs entirely in your browser; nothing is uploaded.

Media Tools

PDF Merge — Merge multiple PDF files into a single document with drag-and-drop reordering, thumbnail preview, and instant download. Free — PDFs never leave your browser.
PDF Split — Split a PDF into separate pages, custom ranges, or hand-picked selections with thumbnail preview and ZIP download. Free tool — PDFs never leave your browser.
PDF Compress — Compress PDF files with adjustable quality to reduce file size while maintaining readability. Free online PDF compressor — files never leave your browser, no signup.
PDF Watermark — Add text or image watermarks to PDF files, customizing font, color, opacity, rotation, and tiling. Free online tool — PDFs never leave your browser, no signup.
PDF Page Organizer — Reorder, rotate, and delete PDF pages with a visual page list. Free online tool — PDFs never leave your browser.
PDF Unlock — Remove owner-password restrictions from PDFs when possible. Free online unlocker — files never leave your browser.
Images to PDF — Convert JPG, PNG, WebP, and GIF images into a single PDF with multiple layout modes, page sizes, and margins. Free converter — images never leave your browser.
PDF to Images — Convert PDF pages to PNG, JPG, or WebP images with DPI control. Select pages, adjust quality, download individually or as ZIP. All processing runs in your browser.
Image Resize — Resize images by percentage or custom dimensions for social posts, web assets, and email. Supports PNG, JPG, WebP input. All processing runs in your browser.
Image Compress — Compress images with adjustable quality and a drag-to-compare preview. Supports PNG, JPG, and WebP. Free online compressor — images never leave your browser.
Image Format Convert — Convert images between PNG, JPG, and WebP formats in seconds. Free online image converter — all processing runs locally in your browser, no upload required.
Image Crop — Crop images with free selection, preset aspect ratios, or exact pixel dimensions. Supports PNG, JPG, and WebP. Free online cropper — images never leave your browser.
Image Rotate — Rotate images by 90°, 180°, or 270° and flip them horizontally or vertically. Supports PNG, JPG, and WebP. Free online rotate tool — images never leave your browser.
Image Metadata — Inspect EXIF and basic image metadata in your browser. Free EXIF viewer — images never leave your device.
Image Split — Split long images into slices with fixed size or manual horizontal/vertical cut lines. Free online splitter — runs in your browser.
Image Stitch — Stitch multiple images into one vertical strip with optional space or overlap. Free online stitcher — images never leave your browser.
Invisible Watermark — Embed or verify invisible text watermarks in image pixels. Free steganography tool — images never leave your browser.
Sketch Board — Draw sketches with pen, shapes, and text, then export PNG. Free online sketch board — drafts stay in your browser.