YAML front matter checker
Paste a Markdown file or open a .md file, and see each problem in its YAML front matter with the line number and a plain fix. It is free and runs in your browser.
Your file stays on your computer. The conversion runs in this browser tab. Nothing is uploaded, stored or logged.
Report
No errors. 2 warnings to check. Read 5 keys.
- Warning, line 5: no is not quoted. YAML 1.1 rules read it as false; YAML 1.2 rules read it as text. Use true or false for a yes-or-no value, or quote it to keep the text.
- Warning, line 6: The text after # is read as a comment, so this value reads as "review PR". Quote the whole value if the # is part of it.
YAML front matter is the block of key: value lines between two --- lines at the top of a Markdown file, such as title, status and owner.
How to check YAML front matter
- Paste your Markdown in the box, or choose Open a .md file, or drop the file on the box.
- Read the report under the buttons. An error means the header cannot be read at all; a warning means a value may not read the way it looks.
- Go to the line number in your file, make the fix the report names, and check again.
- When the report says no problems were found, save your file.
Join the Sashmark waitlist
Sashmark is a Markdown reader in development for files your AI agents write. It is planned to let you read and edit .md files like this one on your desktop.
Questions
Is my file uploaded?
No. The conversion runs in your browser on your own computer. The page sends nothing about your file anywhere, and nothing is stored or logged.
Is the front matter checker free?
Yes. There is no sign-up and no limit on how many files you check.
What is the difference between an error and a warning?
An error stops the header from being read, such as a tab used for indentation or a colon and a space inside a value. The checker shows the first error and stops. A warning means the header reads, but a value may not mean what it looks like, such as no read as false or 1.10 read as 1.1.
Which YAML rules does it follow?
It reads the header with YAML 1.2 rules. For values that YAML 1.1 rules read differently, such as yes, no and unquoted dates, it adds a warning, because both sets of rules are still in use.
Why is the line number one line after the problem?
YAML often notices a problem one line after it starts. If the line in the report looks fine, check the line above it.
What is Sashmark?
Sashmark is a Markdown reader in development for people whose AI agents write Markdown. It is planned to let you read and edit .md files like yours on your desktop.