Free online toolbox for developers

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158+ Developer Tools

158 tools9 CategoriesAlways Free

Mawu (Oltool, oltool.net) is a developer-focused online toolbox launched in 2025, now featuring 158 practical tools across nine categories: cryptography, converters, text processing, math, networking, web tools, PDF tools, image tools, and data conversion. We are committed to privacy-first principles: every tool runs entirely in your browser, with no registration, no installation, and no data leaving your device. Whether you need to quickly parse a JWT token, generate an RFC 4122-compliant UUID, or diff two JSON config files, you will find the right tool here. Forever free, continuously updated.

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Crypto 12

UUID Generator

Generate cryptographically secure UUID v4 and GUID values locally in your browser. Create unique IDs for database keys, tokens and sessions in one click.

Hash Generator

Generate SHA-1/256/384/512 hashes from text with hex output, plus MD5 and RIPEMD-160. Switch between hex and Base64 output, then compare against a published.

HMAC Generator

Compute HMAC signatures with SHA-1/256/384/512 algorithms for API authentication and request signing. Perfect for webhook signatures and API auth flows.

Token Generator

Generate random secure tokens with custom charset, length, and hex or base64 output. Flexible enough for API keys, sessions, nonces and one-time links.

Bcrypt Hash

Hash and verify passwords with bcrypt using custom salt rounds from 4 to 12. Industry-standard password hashing with an adjustable work factor. Cost adjustable.

Password Strength Analyser

Estimate password strength, entropy bits and crack time using zxcvbn analysis. Spot weak passwords before they reach production systems and user accounts.

BIP39 Passphrase

Create 12/15/18/21/24-word BIP39 seed phrases for crypto wallets, compatible with Bitcoin, Ethereum and HD wallet standards and carrying a built-in checksum.

Encrypt / Decrypt Text

Encrypt and decrypt text with AES-GCM using a passphrase via the browser-native Web Crypto API. Keys use PBKDF2 and a fresh salt each run. Base64 output.

RSA Key Pair Generator

Generate RSA key pairs in PEM format via the Web Crypto API with 1024-4096 bit keys. Web Crypto native, exportable PEM keys for any stack or service you use.

ULID Generator

Generate sortable Universally Unique Lexicographic IDs (128-bit, timestamp-based). Time-ordered IDs that sort naturally in databases, logs and indexes.

OTP / TOTP Generator

Generate TOTP codes (RFC 6238) from a base32 secret for 2FA and MFA authentication. Drop-in 2FA codes matching Google Authenticator and Authy or FreeOTP output.

PDF Signature Checker

Inspect digital signature metadata embedded in a PDF with X.509 certificates. Reads certificates issuer signing time and the signed byte range It does not.

Converter 40

Base64 Encoder / Decoder

Encode text to Base64 or decode Base64 back to plain text with full UTF-8 support. Instant bidirectional conversion with one-click copy for any string.

URL Encoder / Decoder

Encode or decode URL-safe strings using percent-encoding for query params and path segments. Essential for building safe query strings and REST API URLs.

Case Converter

Convert text between camelCase, snake_case, kebab-case, PascalCase and CONSTANT_CASE instantly. Switch naming styles for code, configs and identifiers.

Integer Base Converter

Convert numbers between binary, octal, decimal, hex and any base 2-36, with instant results for bitwise ops, colour channels and low-level protocol debugging.

Roman Numeral Converter

Convert between Arabic numbers (1-3999) and Roman numerals instantly. Handy for chapters, outlines, clock faces, movie sequels and classic Roman notation.

Color Converter

Convert colors between HEX, RGB and HSL formats with full alpha channel support. Alpha-aware color translation for CSS, design tools and style guides.

Unix Timestamp Converter

Convert between Unix timestamps and human-readable dates with ISO 8601 output. Essential for log analysis, API debugging and cross-timezone scheduling work.

Text to Binary

Convert text to binary or back via UTF-8 encoding for ASCII and Unicode characters. Handy for low-level debugging, encoding tutorials and CTF puzzles.

Text to Unicode

Convert text to Unicode escape sequences (\uXXXX) and back for UTF-16. Ideal for debugging encoded strings and inspecting raw code points in one pass.

Text to NATO Alphabet

Convert text to NATO phonetic alphabet (Alpha, Bravo, Charlie) for clear radio and phone communication. Spell out words letter by letter with confidence.

YAML to JSON

Convert YAML data to formatted JSON with full nested structure support. Drop in config files for clean, indented JSON you can paste anywhere. Anchors expand.

JSON to YAML

Convert JSON data to YAML format with custom indentation and nested object support. Turn verbose JSON configs into clean readable YAML in a couple of seconds.

JSON Formatter

Beautify, minify and validate JSON data with syntax error detection. Catch malformed brackets and commas before they break your API integration or build.

XML Formatter

Pretty-print and validate XML with custom indentation. Reports the line number for unclosed tags, missing quotes and undeclared namespace prefixes, and can.

SQL Formatter

Format and indent SQL queries with a regex-based prettifier for SELECT, INSERT and UPDATE statements, keeping comments and uppercasing keywords. Keeps comments.

HTML Formatter

Format and beautify HTML code with proper indentation. Supports DOCTYPE, void elements, raw text elements. Beautify or minify. Checks tag nesting Checks tag.

CSS Formatter

Beautify or minify CSS with proper indentation, handling media queries, keyframes and nested rules, and strip comments for production stylesheets and bundles.

JS Formatter

Beautify or minify JavaScript with proper indentation, handling arrow functions, template literals and modern syntax, with a choice of brace style and quotes.

JSON to CSV

Convert a JSON array of objects to CSV with custom delimiters and headers, flatten nested keys and pick which fields to export for spreadsheet and BI tools.

JSON Diff

Compare two JSON documents and highlight deep differences with an inline view for spotting API response changes and configuration drift issues. Copy the report.

docker run to compose

Convert a docker run command into docker-compose.yml with ports, volumes and env vars, so ad-hoc containers become versioned orchestration stacks you can.

List Converter

Sort, dedupe, reverse and transform lists with custom separators and case conversion for cleaning up pasted data and performing repeatable bulk text edits.

JSON Minify

Compact JSON by stripping whitespace and newlines for smaller file size, faster network transfers and reduced payload overhead in JSON API responses and config.

JSON to XML

Convert a JSON document to XML with a custom root element and attributes for legacy system integration, SOAP APIs and enterprise data exchange pipelines.

XML to JSON

Convert an XML document to JSON via DOMParser with attribute and namespace support for modernizing legacy API responses and configuration file processing.

JSON to TOML

Convert JSON to TOML config format with nested tables, arrays and typed values for Rust, Python and other project configuration and manifest file generation.

TOML to JSON

Parse a TOML document into JSON with tables, arrays, dates and multiline strings for inspecting, debugging and migrating project configuration files safely.

YAML to TOML

Convert YAML data to TOML format with nested structures and typed values, handling null explicitly when switching config across toolchains and CI systems.

TOML to YAML

Convert TOML data to YAML format with nested tables, arrays and dates, ready for Kubernetes configs, CI pipeline definitions and deployment manifests.

Base64 File Encoder

Encode any local file to a Base64 data URL for images, PDFs and binary files to embed assets directly in HTML, CSS, JSON and email attachment strings.

JSON to TypeScript

Generate TypeScript interfaces from sample JSON with nested types, arrays and optional fields for typing API responses and configuration or payload objects.

JSON to JSON Schema

Generate a JSON Schema (Draft-07) from sample JSON with properties, required fields and array items for runtime validation and API contract documentation.

JSON to Go Struct

Convert sample JSON to Go structs with json tags, nested types and omitempty option for typing API clients, config loaders and data model definitions.

JSON to Java

Generate Java classes from sample JSON with nested types, List generics, getters/setters and JsonProperty annotations for REST API clients and DTO classes.

JSON to Python

Generate Python dataclass or TypedDict from sample JSON with nested types, List generics and Optional fields for API response typing and config parsing.

JSON to C#

Generate C# classes from sample JSON with nested types, List generics and JsonProperty attributes for .NET models, splitting nested objects into their own.

Lunar Calendar Converter

Convert between Gregorian and Chinese lunar dates, with zodiac, Gan-Zhi, solar terms and leap month support. Check traditional festivals birthdays with zodiac.

Punycode Converter

Convert international domain names to Punycode and back with full RFC 3492 support. Encode IDN domains for DNS and decode xn-- addresses back to Unicode.

Unicode Escape Converter

Convert text to Unicode escape sequences and back, covering classic and ES6 forms, emoji and surrogate pairs. Choose a four-digit or braced ES6 form Choose.

Barcode Generator

Generate barcodes in 20+ formats: CODE128, EAN13, EAN8, UPC, CODE39, ITF14, MSI, pharmacode and more. Download as PNG or SVG and set the checksum in one click.

Web 27

HTML Entities

Encode or decode HTML entities (&, <, >, ", ') for safe rendering, preventing XSS and keeping templating output clean and predictable.

Slugify String

Make strings into URL-safe slugs (lowercase, hyphens, ASCII) with unicode normalization. Build clean permalinks for blogs, docs and landing pages in one click.

JWT Parser

Decode and inspect JWT tokens (header, payload, expiry) with a signature structure check. Inspect auth claims and expiry without sending secrets or keys.

MIME Type Lookup

Look up MIME types by file extension or vice versa for common formats (json, pdf, png). Set correct Content-Type headers and avoid broken browser downloads.

HTTP Status Codes

Reference for HTTP status codes (1xx-5xx) with meanings, examples and use cases. Debug API responses faster by looking up 404, 503 and every other code.

URL Parser

Parse a URL into protocol, host, path, query, hash components with query parsing. Break links apart for redirects, analytics and quick link debugging.

Basic Auth Generator

Turn a username and password into a Base64 Authorization header for curl, Postman and nginx. Copy the header straight into curl. Encode a username Copy.

QR Code Generator

Generate QR codes as PNG data URLs from text or URLs with custom colours and sizes. Embed links, contacts and Wi-Fi credentials in scannable images. PNG output.

Crontab Generator

Build cron expressions with a visual editor and see next run times and plain-language meaning. Debug Linux crontab and Kubernetes CronJobs in seconds.

Open Graph Meta Generator

Generate meta tags for SEO, Open Graph and Twitter cards with a live preview, so share links look right on social platforms and in search results pages.

Safelink Decoder

Decode Outlook and Office365 safelink URLs back to the original links in batch. Strip tracking wrappers and recover the real URLs safely, all locally.

IBAN Validator

Validate IBAN with mod-97 checksum and parse country and bank info for SEPA countries. Verify international account numbers before making cross-border payouts.

JSON Tree Viewer

Browse a large JSON document as a collapsible tree with search and path copy. Drill into deep API responses and copy any node path instantly. Copy any path.

YAML Viewer

Render YAML with a collapsible structure and syntax highlighting. Navigate large config files, search inside the tree, fold branches and copy any node path.

SVG Placeholder Generator

Generate SVG placeholder images as data URLs with custom size, colours and text. Mock up layouts and prototypes before real assets are ready. Save as a file.

Wi-Fi QR Code Generator

Generate QR codes that auto-connect to a Wi-Fi network with full WPA and WEP support, so guests can join by scanning instead of typing a long Wi-Fi password.

Emoji Picker

Browse and copy popular emojis by category with search and skin tone support. Find the right reaction, see its code point and paste it into chat or docs.

Keycode Info

Show the key code and event details for every keypress (keyCode, key, code, location) and copy the values you need for shortcuts, games and other controls.

Device Information

Display browser, OS, screen, GPU and runtime info with viewport, pixel ratio and more. Debug responsive layouts and feature detection checks on the fly.

Camera Recorder

Record video and audio from your webcam using MediaRecorder with WebM or MP4 output. Switch device and frame rate, then save clips locally. Save clips locally.

Open Graph Meta Generator

Build Open Graph and Twitter Card meta tags with a live preview, so you can see exactly how share cards render before you ship the page. Copy the tags.

cURL to Code

Convert cURL commands to Python, JavaScript, PHP, Go, Java code with auth and JSON body. Turn terminal snippets into runnable client code in a few seconds.

JSONPath Finder

Test and extract data from JSON with JSONPath expressions in real time, with examples and match count for building and debugging complex nested queries.

JavaScript Runner

Run JavaScript in your browser with console output capture. The sandbox isolates execution from the page and keeps a history so you can rerun experiments.

Image Cropper

Crop images to exact dimensions or aspect ratios like 1:1, 16:9 and 4:3 with a drag-to-select editor. Lock the ratio and export PNG, JPEG or WebP in one click.

Image Watermark

Add text watermarks to images with control over position, opacity, font size and rotation. Place the mark in a corner or tile it across the whole image.

Color Palette Generator

Generate color palettes from a base color with complementary, analogous, triadic and monochromatic schemes. Export HEX, RGB and HSL as JSON, CSS or TXT.

Text 25

Text Statistics

Count characters, words, lines, bytes and estimate reading time with sentence analysis to gauge content length and overall readability at a single glance.

String Obfuscator

Obfuscate text by replacing middle characters with asterisks for emails, phones and credit cards to protect sensitive data in logs, tickets and screenshots.

Markdown Preview

Render Markdown to HTML in real time with markdown-it, GFM, code blocks and tables, a live writing companion for documentation, drafts and README files.

ASCII Banner (Figlet)

Generate large ASCII-art text banners with figlet fonts and custom styles, choosing from dozens of built-in fonts and exporting as plain text for scripts.

Numeronym Generator

Convert words to numeronyms like i18n, k8s, a11y and l10n for compact abbreviations, and batch convert a list while keeping the original casing and separators.

String Pluralizer

Convert English nouns between singular and plural forms, including irregular nouns, for dynamic labels and grammatically correct UI labels and output.

Email Normalizer

Normalize emails by lowercasing, removing Gmail dots and plus-aliases with RFC validation, for deduping mailing lists and cleaning user records. Dedupe ready.

Text Diff

Compare two text blocks line-by-line using the LCS algorithm with inline highlighting to review edits and merge conflicting changes side by side in one view.

Regex Tester

Test JavaScript regular expressions with flags like g, i, m, s and u plus capture groups, listing every match and named group as you type. All hits listed.

Regex Cheatsheet

Quick reference for JS regex syntax, character classes, anchors, quantifiers and lookarounds, a handy cheat sheet for writing and debugging match patterns.

Git Cheatsheet

Quick reference for common git commands like init, commit, branch, merge and rebase for daily version control workflow and day-to-day troubleshooting lookups.

HTML WYSIWYG Editor

Visual rich-text editor that outputs clean HTML with bold, italic, lists and links for drafting emails, blog posts and content management systems alike.

Fake Data Generator

Generate mock names, emails, phones, addresses and IDs in JSON or CSV for testing, prototyping and database seeding. Set field combinations and row counts.

AI Prompt Generator

Generate structured AI prompts with role, task, context, tone and format constraints, helping you build better prompts for ChatGPT, Claude and other LLMs.

Text to Speech

Convert text to speech using the Web Speech Synthesis API. Choose from available voices, adjust speed and pitch. Adjust rate pitch and voice and English text;.

Lorem Ipsum Generator

Generate Lorem Ipsum or Chinese filler text as paragraphs, sentences or words, with a configurable count plus copy and plain-text download. Copy or download.

Text Replacer

Find and replace text with case-sensitive, whole-word and regex matching. Replace all at once with live preview, and review every hit before applying.

URL Extractor

Extract all URLs from any text, detecting http, https, www and bare domains. Get a deduplicated list from web page source, chat logs or documents in one pass.

Email Extractor

Extract all email addresses from any text, validate the format and remove duplicates. Works on pasted page source and contact lists, ready to export in one.

Duplicate Line Remover

Remove duplicate lines from text while preserving order, with case-sensitive mode. Shows how many were removed. Keep first occurrences in order Keep first.

Empty Line Remover

Remove empty or blank lines from text and optionally trim whitespace per line. Clean up pasted logs, code or notes in one click and download the result.

Chart Generator

Create bar, line and pie charts from CSV or JSON with custom colors, and export as PNG or SVG.，Handy for text cleaning, format conversion and content.

Line Chart Generator

Create line charts from CSV or JSON with multiple series, smooth curves and area fill. Paste CSV or JSON add multiple series switch between straight Paste CSV.

Pie Chart Generator

Create pie and donut charts from your data with custom colors, labels and legend. Label slices with values or percentages and redraw the chart as data changes.

Image OCR

Extract text from images with Tesseract.js in 60+ languages including Chinese and Japanese. Select a region to improve accuracy, then copy the text out.

Math 12

Percentage Calculator

Calculate percentages, increase or decrease, ratios and change between values with multiple modes for everyday maths and financial quick checks. Five results.

Math Evaluator

Evaluate math expressions safely without eval, supporting functions, operators and parentheses for quick calculations and formula prototyping as you type.

Date Calculator

Add or subtract days, diff dates and format dates with time zone support, optionally skipping weekends and holidays for scheduling and deadlines. Skip weekends.

Temperature Converter

Convert between Celsius, Fahrenheit, Kelvin and Rankine with decimal precision, showing the formula so you can check science, cooking and weather data.

ETA Calculator

Compute estimated time of arrival from rate and remaining work with custom units for sprint planning and long-running batch task progress projections.

Chmod Calculator

Convert between octal and rwx Unix permission notation with special bits support, showing the owner, group and other bits for secure file permissions.

Chronometer / Stopwatch

Stopwatch with start, pause, lap and reset at millisecond precision for timing tasks, workouts and code execution, with records that survive tab reloads.

Benchmark Builder

Compare multiple operations-per-second measurements and rank them with statistical analysis, showing sample counts and variance rather than trusting one run.

Unit Converter

Convert length, weight, area, volume, speed and data storage units across metric and imperial systems with instant bidirectional swap for any everyday task.

Stats Calculator

Compute count, sum, mean, median, mode, min, max, range, variance and standard deviation from a list of numbers for data analysis, reports and stats homework.

Compound Interest Calculator

Calculate compound interest with regular monthly contributions, adjustable compounding frequency and final amount, total principal and effective return rate.

Timezone Converter

Convert any moment between world time zones with a live clock for UTC, Shanghai, Tokyo, London and more. Schedule across regions and time zones with confidence.

Network 12

MAC Address Generator

Bulk-generate spec-compliant random MAC addresses with a vendor OUI prefix and colon, hyphen or dot separators, then copy the whole batch in one click.

Random Port Generator

Pick valid non-system ports in one click with bulk export, dedupe and range filtering. Choose your own range filter reserved ports batch-generate Choose.

IPv4 Subnet Calculator

CIDR calculator showing network, broadcast, host range, mask and wildcard for any prefix from /0 to /32, essential for network planning and firewalls.

Phone Parser & Formatter

Parse, validate and format international phone numbers into E.164 with country codes for contact forms, CRM imports and bulk data cleanup or migration work.

User-Agent Parser

Parse User-Agent strings into browser, OS and device info with Chrome, Firefox and Safari detection, and flag likely bots for cleaner traffic and log analysis.

IPv6 ULA Generator

Generate IPv6 unique local addresses in the fd00::/8 range with a custom subnet ID and EUI-64, for homelabs and private networks that stay stable over time.

IPv4 Address Converter

Convert IPv4 between dotted, decimal, hex and binary formats with reverse DNS, useful for network debugging, protocol analysis and subnet planning work.

IPv4 Range Expander

Expand CIDR notation to a full list of individual IP addresses with clean bulk export, ready for firewall rules, network scans and access control lists.

MAC Address Vendor Lookup

Look up the vendor, country and organization behind any MAC address by OUI prefix using the IEEE registry. Paste a full address or just the first three bytes.

IP Query

Look up IP address information including country, region, city, ISP and coordinates. Auto-detect your current IP or query any address against public databases.

DNS Lookup

Query DNS records including A, AAAA, MX, TXT, NS, CNAME, SOA and CAA via Google or Cloudflare DoH. Inspect record name, type, TTL and data in one click.

Bandwidth Calculator

Compute download time, speed or file size from the other two with Mbps, Gbps, MB, GB and TB units, and see when bits are confused with bytes. Any two units.

Data 5

Data Format Converter

Convert between JSON, YAML, TOML, XML and CSV in one place with a single paste and instant preview for seamless multi-format config and data conversion.

Excel to JSON

Convert Excel files (xlsx, xls, csv) to JSON format. Supports nested headers, sheet selection and key mapping. Choose the sheet and header row and keep numbers.

Excel to CSV

Convert Excel files to CSV with custom delimiter options and batch sheet conversion. Export data for databases or scripts via SheetJS, in the browser.

Excel to HTML

Convert Excel to clean, styled HTML tables with sheet selection and responsive output. Pick a sheet keep merged cells Choose which sheet to export Pick.

Excel to Text

Extract plain text from Excel with tab or custom delimiter output and batch sheet processing. Choose tab or a custom delimiter process several sheets at once.

Image 11

Image Compressor

Compress PNG, JPEG and WebP images in your browser with an adjustable quality slider, batch processing and before-and-after file size preview. Batch friendly.

Image Format Converter

Convert images between PNG, JPEG and WebP formats with quality control and white background fill for JPEG transparency and browser compatibility handling.

Image Color Picker

Pick colors from any image with an eyedropper tool, get HEX, RGB and HSL values and maintain a running history of all your previously sampled colour values.

Image Resizer

Resize images to custom width and height while optionally keeping the aspect ratio. Scale to an exact target size and export PNG, JPEG or WebP files in one.

Image Merger

Combine multiple images into one with a custom layout, gap and background. Lay images out in a row, a column or a grid and preview the result first in one.

Image Round Corners

Add rounded corners to images with a customizable radius and transparent PNG output. Set the radius apply the same settings to a batch Great for avatars.

Image Border

Add borders to images with custom width, color and style, including solid, dashed or dotted. Choose width colour and a solid dashed or dotted style Choose.

Image to ICO

Convert PNG, JPEG or WebP to ICO favicon format, with a full icon set from 16x16 to 256x256 packed into one .ico file so browsers pick the right size.

Image to GIF

Turn multiple images into an animated GIF with an adjustable delay, loop count and playback order, from PNG, JPEG or WebP. Preview before you export in one.

GIF Compressor

Compress animated GIFs by reducing the colour count, frame rate and dimensions, then compare size and quality side by side to pick the right balance .

GIF Cropper

Crop animated GIFs to a specific area with a visual selection box that keeps the animation. Drag a selection box lock the ratio if needed while loops Drag.

PDF 14

PDF Merger

Merge multiple PDF files into one document in your browser. Drag files into order check page counts for each document merge then download one file all locally.

PDF Splitter

Split a PDF by page ranges or extract individual pages. Preview page count, export selected pages as a new PDF. Pure browser processing powered by pdf-lib.

PDF Rotator

Rotate PDF pages 90, 180 or 270 degrees. Select specific pages or rotate all, then download the rotated file instantly without re-rendering content in one.

PDF Watermark

Add text watermarks to PDFs with custom font, size, color, opacity, rotation and position. Tile across all pages or place it in a corner, all browser-based.

PDF Encrypt

Add password protection to PDFs with user/owner passwords and permissions. Set separate open and permissions passwords then restrict printing copying Set.

PDF Decrypt

Remove password protection from a PDF by entering its current password. Enter the current password to remove protection and download an unlocked copy;.

PDF Page Numbers

Add page numbers to PDFs with custom position, font size, format and start page. Choose position font size format and start number Preview before saving.

PDF Page Deleter

Delete specific pages from a PDF on a thumbnail grid and download the cleaned file. Pick pages visually or type a range and preview the count first in one pass.

PDF to Image

Convert each PDF page into a PNG or JPEG and download all pages as a zip or individually. Turn reports and scans into reusable pictures in the browser.

PDF Compress

Compress PDF files with three quality levels, strip metadata and thumbnails to reduce size, and compare the file size and page quality before and after.

PDF Page Organizer

Reorder or delete PDF pages on a thumbnail grid, then download the cleaned document. Drag thumbnails to reorder delete pages you do not need Merge files first.

PDF Extract

Extract specific pages from a PDF by page range, keep the original file untouched and download the selection as a new PDF, all in the browser. Ranges supported.

PDF Sign

Add electronic signatures to PDF documents. Draw with mouse or touch, or upload a signature image, then customise the position, size and target page in one.

PDF Crop

Crop PDF pages to remove white margins or adjust visible area. Auto-detect margins or set custom values. Apply to all or selected pages. Trims scanned borders.