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JustDevTools
  • JSON formatter and validator
    Format, minify and validate JSON, with the exact line and column of any syntax error.
  • JWT decoder
    Read a JWT's header and payload, with issued-at and expiry times shown as real dates.
  • Base64 encoder and decoder
    Encode and decode Base64 and Base64URL, with full Unicode support.
  • JSON to TypeScript, Zod and Java
    Paste a JSON response and get TypeScript interfaces, a Zod schema or Java classes with Jackson annotations.
  • YAML to JSON converter
    Convert YAML to JSON and JSON to YAML, with the exact line of any syntax error. Handles multi-document files.
  • Regex tester
    Test JavaScript regular expressions with live match highlighting, capture groups and replace preview.
  • URL encoder and decoder
    Percent-encode and decode URLs and query values, and break a URL into its parts and parameters.
  • Unix timestamp converter
    Convert Unix timestamps in seconds or milliseconds to dates, and dates back to timestamps.
  • Cron expression explainer
    See what a cron expression means in plain English, what each field does and the next times it will run.
  • JSON to CSV converter
    Turn a JSON array into CSV for Excel or Google Sheets, or a CSV file into JSON. Nested objects become columns.
  • UUID generator and inspector
    Generate UUID v4 and time-ordered v7 in bulk, or paste a UUID to see its version and timestamp.
  • Text diff checker
    Compare two texts line by line and see exactly what was added, removed or changed.
  • Hash and HMAC generator
    SHA-256, SHA-1, SHA-384 and SHA-512 hashes and HMAC signatures of text, in hex or Base64.
  • Markdown previewer
    Write Markdown on the left and see it rendered live on the right, with GitHub-style tables and task lists.

Markdown previewer

Write Markdown on the left and see it rendered live on the right, with GitHub-style tables and task lists.

Runs locally. Nothing you paste leaves this tab.

Preview

Hello, Markdown

Type on the left and the preview updates as you type.

  • Lists
  • Italic and bold
  • inline code
Tool Status
Markdown Done
  • ☑ Build the page
  • ☐ Build the HTML previewer

What Markdown is

Markdown is a plain-text way to write formatted documents. You type # for a heading, **bold** for bold and - for a list item, and a renderer turns it into HTML. README files, GitHub issues, pull requests, wikis and most documentation sites use it.

The syntax you'll use most

# Heading 1
## Heading 2

**bold**, *italic*, `inline code`

- a bullet
- another bullet

1. numbered
2. list

[a link](https://example.com)

> a quote

GitHub Flavored Markdown

GitHub Flavored Markdown (GFM) adds tables, task lists, strikethrough and automatic links to the original syntax. This previewer supports all of them, so what you see here is close to what GitHub will show. 

| Tool     | Status |
| -------- | ------ |
| Markdown | Done   |
| HTML     | Next   |

- [x] finished task
- [ ] open task

~~struck out~~

Is it safe to paste HTML?

Markdown allows raw HTML. Anything unsafe, such as <script> tags or onclick attributes, is removed before the preview is shown, so pasted content cannot run code on this page.