maratoolDeveloper tools
Free browser-based developer utilities — crypto, IDs, scheduling, references. Everything runs locally — no data leaves your device.
Most used in Developer
Test Regex Patterns Online
Test regular expressions with live match highlighting.
Format and Validate JSON Online
Format, minify and validate JSON instantly.
Generate MD5 SHA-256 Hash Online
Generate MD5, SHA-1, SHA-256, and SHA-512 hashes from any text input instantly.
Decode JWT Token Online
Decode and inspect JWT tokens instantly — view header, payload, and signature.
Bcrypt Generator
Hash passwords with bcrypt in your browser. Choose cost factor, generate secure hashes, and verify passwords. No upload — runs locally.
Password Generator
Generate cryptographically secure passwords with custom length, character sets, and strength check. Fully offline — no data ever leaves your browser.
Meta Tag Generator
Generate HTML meta tags for SEO and social sharing. Covers title, description, canonical, Open Graph, and Twitter Card tags.
Robots.txt Generator
Generate a valid robots.txt file for your website. Control which bots can crawl your pages, block AI scrapers, and add your sitemap URL.
Schema Markup Generator
Generate JSON-LD structured data for Article, Product, FAQ, HowTo, LocalBusiness, and more. Copy and paste into your HTML head.
Check Meta Tags Online
Paste page HTML to audit title, description, canonical, Open Graph, and Twitter tags. Paste-only — cannot fetch live URLs.
Preview Open Graph Link Cards
Preview how your page looks when shared on social — paste HTML or enter OG fields manually. Cannot fetch live URLs.
Test Robots.txt Rules Online
Paste robots.txt and test if a URL path is allowed or blocked for a crawler. Paste-only — cannot fetch live robots.txt.
Validate Sitemap XML Online
Paste sitemap XML to validate structure, URLs, and duplicates. Does not fetch live sitemaps or check HTTP status codes.
Validate Schema Markup Online
Paste JSON-LD to validate syntax and required schema.org fields. Paste-only — cannot fetch live pages or replace Google Rich Results Test.
API Key Generator
Generate cryptographically secure API keys in hex, base64, or alphanumeric formats. Runs offline in your browser.
Generate UUID v4 Online
Generate one or many UUIDs instantly — supports v1, v4, and v5.
Cron Expression Builder & Decoder
Build and decode cron expressions with a visual editor.
Number Base Converter
Convert numbers between decimal, hexadecimal, binary, and octal instantly. Supports integers and fractions.
Calculate AI API Cost Online
Estimate per-request cost for GPT-4o, Claude, Gemini, and more. Enter token counts and see input, output, and total pricing.
Tailwind CSS Cheat Sheet
Quick reference for Tailwind CSS classes — spacing, typography, colors, flexbox, grid, and more. Search and copy any class.
SQL Formatter — Beautify SQL Online
Format and beautify SQL queries instantly. Paste messy SQL and get indented, readable output.
cURL Command Generator
Build cURL commands from URL, method, headers, and body. Copy-ready curl for any HTTP request.
Password Strength Checker
Check password strength with entropy scoring and crack-time estimates. See what makes a password weak or strong.
HMAC Generator — SHA-256 & SHA-512
Generate HMAC signatures with SHA-256, SHA-384, or SHA-512. Enter message and secret key — runs in your browser.
AI Context Window Calculator
See how much of a model context window your text uses. Compare GPT-4o, Claude, and Gemini token limits.
JSON Diff — Compare Two JSON Objects
Compare two JSON documents and highlight added, removed, and changed keys. Formatted side-by-side diff.
Convert cURL to JavaScript Fetch
Convert cURL commands to JavaScript fetch() code. Paste curl and get copy-ready fetch syntax.
Convert cURL to Python Requests
Convert cURL commands to Python requests code. Paste curl and get copy-ready Python.
Postman Collection Generator
Generate Postman Collection v2.1 JSON from URL, method, headers, and body. Import directly into Postman.
JSON Schema Validator Online
Validate JSON data against a JSON Schema. Paste instance and schema to see errors instantly.
Prompt Variable Tester — Template Preview
Test prompt templates with variables. Enter {{placeholders}} and preview the filled prompt instantly.
AI Embedding Cost Calculator
Estimate embedding API costs for OpenAI, Cohere, and Voyage. Enter token count and see per-request pricing.
SQL Minifier — Compress SQL Online
Minify SQL queries online. Remove comments and whitespace for smaller payloads. Free SQL minifier, runs in your browser.
SQL INSERT Generator from JSON
Generate SQL INSERT statements from JSON arrays. Paste JSON and get copy-ready INSERT queries. Free, runs in your browser.
SQL CREATE TABLE Generator from JSON
Generate CREATE TABLE SQL from JSON schema or sample rows. Infer column types instantly. Free browser tool.
RAG Chunk Calculator — Vector Chunk Size
Calculate RAG chunk count from token total, chunk size, and overlap. Plan vector indexing splits in your browser.
AI Model Cost Comparison
Compare LLM API costs across OpenAI, Claude, and Gemini for the same token counts. Free browser calculator.
Extract JSON from LLM Output
Extract JSON from LLM responses. Parse fenced code blocks and inline objects from pasted model output.
Hash Identifier — Detect Hash Type
Identify hash types from pasted digests. Detect MD5, SHA-256, bcrypt, and more. Paste only, runs in browser.
IBAN Validator Online
Validate IBAN numbers with mod-97 check digits. Paste an IBAN to verify format and checksum. Free browser tool.
Luhn Checker — Credit Card Validation
Validate numbers with the Luhn algorithm. Check credit card and identifier check digits. Paste only, in browser.
JWT Security Checker — Audit Tokens
Audit pasted JWT tokens for security issues. Flag alg none, expiry, and missing claims. Runs in your browser.
HTML Minifier Online
Minify HTML by removing comments and extra whitespace. Paste HTML and copy compressed output. Runs in browser.
HTML Beautifier — Format HTML Online
Beautify and indent pasted HTML for readability. Format messy markup instantly. Free, runs in your browser.
CSS Minifier Online
Minify CSS stylesheets online. Remove comments and whitespace from pasted CSS. Free browser minifier.
URL Parser — Decode URL Components
Parse URLs into protocol, host, path, query, and hash components. Paste any URL for instant breakdown.
Vision Image Token Estimator
Estimate how many tokens an image costs a vision model from its dimensions, so a batch of screenshots does not surprise you on the bill.
JSON Schema Generator from JSON
Infer a JSON Schema from a sample document, giving you types, required fields and nested structures as a draft to tighten by hand.
Clean Up Markdown Text Online
Fix the damage pasted Markdown picks up: smart quotes, non-breaking spaces, inconsistent list markers and headings stuck to the paragraph above.
Compare Two Prompts — Prompt Diff
Put two prompts side by side and see exactly which words changed, so you know what you actually varied before blaming the model for the difference.
Compare Prompt Versions
Track a prompt across revisions and see what each edit changed, which is the only way to attribute an output shift to the edit that caused it.
Format AI Output — JSON & Markdown
Paste the JSON or Markdown a model handed back with its stray prose, code fences and trailing commas, and get a clean, indented block out.
SQL Query Builder — SELECT Generator
Assemble a SELECT from tables, columns, joins and conditions and read the SQL it produces, which is a faster way to learn joins than staring at syntax.
Convert CSV to SQL INSERT Statements
Turn a CSV into INSERT statements with a table name you choose, quoting strings and leaving numbers bare so the script runs as written.
Convert SQL INSERT to CSV
Pull the values out of a block of INSERT statements and get CSV rows back, for when a dump is all you have and you need the data in a spreadsheet.
ER Diagram Generator from Schema
Paste a schema and get an entity relationship diagram back, with the foreign keys drawn as the links between tables rather than left in the DDL.
Convert MongoDB JSON to SQL
Translate MongoDB documents into relational rows, mapping nested fields to columns so a collection can be loaded into a SQL table.
HTTP Request Builder — Raw & cURL
Assemble a request from method, URL, headers and body, then take it away as a raw HTTP message or as a cURL command ready to paste in a terminal.
API Mock JSON Response Generator
Describe the shape you want and get a JSON response body to point a client at, so front-end work can start before the real endpoint exists.
Webhook Payload Inspector
Paste a webhook body and see it parsed into a readable tree, with the headers and signature fields separated from the event data.
Compare Two Hashes Online
Paste two hashes and get a straight match or no match, instead of squinting at 64 hex characters and trusting your eyes.
Checksum Calculator — SHA-256 & More
Hash a file or a string with MD5, SHA-1, SHA-256 or SHA-512 and compare it against a published checksum to confirm the download arrived intact.
SSL Certificate Decoder — Paste PEM
Paste a certificate and read the subject, issuer, validity window, subject alternative names and key details in plain text.
CSR Generator — RSA Key Pair
Generate an RSA key pair and the matching certificate signing request in your browser, with the private key never leaving the page.
PEM Decoder — Parse PEM Blocks
Decode a PEM block and read what is inside it: certificate subject and dates, key parameters, or the fields of a signing request.
Certificate Expiration Checker
Paste a PEM certificate and see the not-before and not-after dates, plus how many days are left, before a renewal quietly slips past.
Open CRX File Online
Open a Chrome extension file and read what is inside it: the manifest, every permission in plain English, and the full source of every file.
HTML Preview Online
Paste HTML and see it rendered next to the source, so you can check a fragment or an email template without saving a file and reloading.
CSS Beautifier Online
Paste minified or badly indented CSS and get it back with one declaration per line, consistent indentation and the braces where you expect them.
JavaScript Minifier Online
Strip comments, whitespace and line breaks out of JavaScript to cut the bytes a browser has to download, without touching what the code does.
HTML Structure Validator
Check markup for unclosed tags, badly nested elements and misplaced block content, the structural errors browsers silently paper over.
CSS Grid Generator
Set columns, rows and gap visually and copy the grid-template-columns and grid-template-rows rules straight into your stylesheet.
Flexbox CSS Generator
Set justify-content, align-items, direction and wrap against a live preview and copy the flexbox rules once the layout looks right.
SVG Viewer & Editor Online
Open an SVG, see it rendered next to its markup, and edit the paths, fills and viewBox with the preview updating as you change the code.
CSV Diff — Compare Two CSV Files
Paste two CSV files side by side and see which rows were added, removed or changed, instead of scanning two spreadsheets by eye.
XML Validator Online
Check XML is well formed, catching unclosed tags, mismatched element names and stray characters that break a parser before it reads any content.
YAML Validator Online
Check YAML parses, and catch the indentation and tab errors that make a config file fail at deploy time rather than at the moment you saved it.
TOML to JSON Converter
Convert TOML config into JSON and back, for when a tool wants one format and your config lives in the other.
XML Formatter Online
Paste flattened or badly indented XML and get it back with each element on its own line and nesting you can actually follow.
JSON Flatten — Nested to Dot Notation
Turn a deeply nested object into flat dot-notation keys, the shape config loaders, feature flags and spreadsheets all expect.
JSON Path Tester Online
Run a JSONPath expression against your own document and see the matches highlighted, so you can get the selector right before it goes into code.
HTML Escape and Unescape Online
Escape HTML special characters to entities or decode them back, covering named, decimal, and hexadecimal references without touching innerHTML.
Random Number Generator
Pick random numbers in any range using the browser cryptographic random source. Integers or decimals, with or without repeats.
Slug Generator — Convert a Title to a URL Slug
Turn a headline into a URL-safe slug: accents folded to ASCII, punctuation dropped, optional stop-word removal, and truncation on a word boundary.
URL Encode and Decode Online
Percent-encode text for a URL or decode %20 and %C3%A9 back to readable characters, with a toggle between encodeURIComponent and encodeURI.
iPhone Duo Simulator
Preview a page at the iPhone Duo's folded and unfolded CSS viewports, side by side, with the breakpoint each state lands on.
About these developer tools
This page collects the small utilities that come up over and over in day-to-day engineering work — encoding and decoding tokens, hashing strings, generating identifiers, building cron schedules, testing regular expressions, and producing secure random values. They are the kind of tasks that interrupt real work for thirty seconds, and a fast, browser-based tool is usually faster than writing a one-off script or opening an IDE.
What you can do here
The tools split roughly into four jobs. Inspection tools read structured data and show you what is inside — for example, the JWT decoder splits a token into its header, payload, and signature so you can verify claims, audience, and expiry without a debugger. Generation tools produce values on demand: the UUID generator emits v1, v4, and v5 identifiers in bulk, and the password generator uses the browser's cryptographic random source rather than Math.random. Hashing tools compute fingerprints — the hash generator covers MD5, SHA-1, SHA-256, and SHA-512 at once, useful for checksums, cache keys, and integrity checks. Reference tools sit alongside, like the cron expression builder and the regex tester, which let you preview a schedule or a pattern before you commit it to production.
When to use which
Reach for the JWT decoder when you need to read a token you already have. Use the hash generator when comparing file fingerprints or producing stable cache keys. Use the UUID generator when seeding a database or writing fixtures. Use the regex tester when a pattern works in one engine but not another, or to debug a backreference that is matching the wrong group. Each tool keeps state in the URL or in localStorage where it makes sense, so you can paste the page link into a ticket or come back to it later without losing context.
Privacy
Everything on this page runs in your browser. Tokens, plaintext, generated identifiers, and any input you paste stay on your device — nothing is sent to a server, logged, or stored remotely. That makes these safe to use on real production credentials, internal API responses, or anything else you would not want flowing through a third party.