Markdown Frontmatter Parser

Extract, parse, and analyze YAML frontmatter blocks and preview the rendered Markdown content securely.

Markdown Editor

Markdown with YAML Frontmatter

Size: 568 bytesLines: 22

Property Key	Data Type	Value
title	string	Getting Started with Zeroserver Tools
date	string	2026-06-11
author	string	Meet Shah
tags	array	developer-toolsproductivity
draft	boolean	false
rating	number	4.8
description	string	A quick guide to the free online tool suite.

Deep Dive: YAML Frontmatter Parsing

YAML Frontmatter is a widely used configuration layout for documentation files, static posts (Jekyll, Hugo, Astro, Next.js), and CMS tools. It is enclosed between opening and closing triple hyphens (---) at the start of a Markdown file. It sets crucial variables like authors, dates, keywords, categories, and custom template properties.

This parser breaks down the frontmatter block, processes scalars (booleans, floats, integers, strings), and handles structured YAML arrays. Sandboxed live iframe previews protect against DOM-XSS attacks by preventing browser script execution, while preserving CSS color-scheme queries for dark-mode.

Built and maintained by Meet Shah · Last updated 1 August 2026

What this tool is used for

Extracting frontmatter from a Markdown file to see the fields it declares.
Checking how a value's type will be inferred by a static site generator.
Comparing frontmatter across a set of posts for consistency.
Debugging a build that fails on one file's frontmatter.
Producing JSON from a post's metadata for a build script to consume.

Frequently Asked Questions

What counts as a frontmatter block?: Three dashes on the very first line, key-value pairs, then a closing three dashes on their own line. The parser trims the document first, so a leading blank line is tolerated — but text before the opening delimiter is not, and the block is then treated as ordinary body content.
Which YAML features are supported?: Scalars and simple block sequences — the indented `- item` form under a key with no inline value. Strings, numbers, booleans, `null` and `~` are recognised and typed. Nested maps, anchors, multi-line block scalars and flow sequences are beyond this parser.
Why is my version number showing as a number?: Because any value that survives `Number()` is stored as one, so `1.0` becomes 1 and the trailing zero disappears. Quote it — `version: "1.0"` — and it stays a string. This is the same trap YAML itself has with unquoted version strings and country codes.
Does the preview run the Markdown safely?: The body is compiled with marked and rendered inside a sandboxed iframe rather than injected into the page, so script in a pasted document cannot reach this page's DOM or storage. The parsing itself happens in your browser; nothing is uploaded.
What does the JSON tab give me?: The parsed frontmatter as a JSON object, which is the shape a static-site generator or content API would hand your templates. It is useful for checking that a field you expect to be an array really parsed as one rather than as a single string.
Why is a key with a colon in its value truncated?: It is not — the key is matched up to the first colon and everything after it is the value, so `description: Tools: a guide` keeps the full text. A colon in the KEY is what breaks, because there is no way to tell it apart from the separator without quoting.

Common errors and gotchas

Being caught by YAML's implicit typing, where an unquoted date or version changes type.
Omitting the closing delimiter, which makes the whole file body part of the frontmatter.
Using tabs for indentation, which YAML forbids.
Assuming one delimiter convention, since TOML and JSON frontmatter also exist.
Putting a colon in an unquoted value, which YAML reads as a key separator.