Have you ever pushed a config file and watched a build fail over one stray tab? YAML cares about spacing, and small slips can break the whole file. The YAML Validator runs a fast line check for two common spacing mistakes.
This tool is for developers, DevOps engineers, and anyone editing config files by hand. You paste YAML into the box, and the report updates as you type. It is a quick first pass, not a full parser.
Table of Contents
- What the Tool Checks
- How to Use It, Step by Step
- How the Check Works
- Worked Example
- How to Read the Results
- List Items and the Colon Check
- Limitations and Assumptions
- FAQs About the YAML Validator
What the Tool Checks
The YAML Validator reads your text one line at a time. It looks for two problems and counts a few things for you.
- Tab Indentation: it flags a line indented with a tab, since YAML wants spaces.
- Missing Space After Colon: it flags a key with no space between the colon and its value.
- Total Lines: the total number of lines, including blank lines and comments.
- Keys Identified: a count of lines that hold a real key and a mapping colon.
- Validation Status: it reads Passed, a count of issues, or Empty.
The tool does not read the full document. A Passed result means no tab or spacing issue was found, nothing more.
How to Use It, Step by Step
- Open the tool. A sample config with a server, database, and tags block is already loaded.
- Delete the sample and paste your own YAML into the Raw YAML Input box.
- Watch the Validation Report on the right update as you type.
- Read the three cards at the top for line count, key count, and status.
- Fix any flagged line, then check that the status turns green again.
- Use Clear to empty the box, or Copy Report to copy the result text.
How the Check Works
The tool splits your text on each line break. It skips blank lines and lines that start with a hash mark. For every other line, it runs two simple tests.
Each Line→Skip Blank or Comment→Tab Check Plus Colon Space Check=Report
- Tab test: if the leading whitespace holds a tab, the line is flagged.
- Colon test: it finds the first colon on the line, then checks for a space after it.
- Key count: it strips any leading dash, then counts a real mapping colon.
A mapping colon is one that ends the line or has a space after it. So a colon inside a value, like a web address, does not count as a key. The colon test is skipped on any line that starts with a dash.
Worked Example
Priya pastes a short config to check her spacing. Here is what the tool reports for part of it.
| Input Line | Result |
|---|
| server: | Counted as a key, no error |
| host: localhost | Counted as a key, space after colon is fine |
| port: 8080 | Counted as a key, no error |
| database: | Counted as a key, no error |
| name: main_db | Counted as a key, no error |
The full sample has 10 lines and 8 keys, and the status reads Passed. The report says it found no tab or colon-spacing issue.
If Priya changes one line to name:main_db with no space, the report shows one issue on line 5. That broken line no longer counts as a key, so the key total drops to 7. The status then reads 1 Issue in red.
If she adds a tab in front of a line, the tool flags it. The message reads Tabs used for indentation (YAML requires spaces).
How to Read the Results
Total Lines is every line in the box. Blank lines and comment lines are part of this total, so it is not a count of fields.
Keys Identified is a tally of real keys. It now includes keys written inside dashed list items, such as a name under a list.
Validation Status is the quick verdict. A green Passed means both checks found nothing, while a red count lists each flagged line by number.
List Items and the Colon Check
A list item with a URL or a clock time holds a colon inside its value. An earlier version read that colon and flagged the valid line by mistake.
To stop those false errors, the tool now skips the colon test on any line that starts with a dash. So a line like - http://example.com passes cleanly.
A key with a URL value is still checked, since its first colon sits right after the key name. The line website: http://example.com passes with no error. If you want tidy spacing first, the YAML Formatter cleans up indentation. The YAML Viewer shows a large file in a clear layout.
Limitations and Assumptions
- This is a line checker, not a full YAML parser. It tests only tabs and colon spacing.
- Many broken files still pass, since the two checks cannot judge real structure.
- The colon test is skipped on list items, so it reads only key lines for spacing.
- Total Lines includes blank and comment lines, so it is not a count of fields.
- A blank box shows an Empty status and asks you to enter content.
For real schema or type checks, run your file through your own build tools. If you move data between formats, the YAML to JSON and JSON to YAML tools handle that step. To check structured data in another syntax, the JSON Validator may help. More utilities live in the Developer Tools hub.
FAQs About the YAML Validator
Why Does the Status Read Passed Instead of Valid?
The tool runs only two checks, so it cannot promise real YAML validity. The status reads Passed to show those checks found nothing. A real parser may still reject the file.
Does It Catch Every Missing Space?
No. The tool skips the colon test on lines that start with a dash. So a missing space inside a list item, like a dashed key with no space, is not flagged.
What Does Keys Identified Leave Out?
It skips a colon inside a value, such as a web address or a clock time. It also skips a key line that has no space after the colon, since that line is broken.
Can It Find Duplicate Keys or Missing Brackets?
No. Duplicate keys, broken nesting, and unclosed brackets are never checked. A file with those problems can still show a green Passed status here.
Does My YAML Leave the Browser?
No. The check runs with JavaScript on your own device. Nothing you paste is sent to a server or saved after you close the tab.
What Does the Copy Report Button Do?
It copies the report text to your clipboard and shows a Copied note. If your browser blocks that, it falls back to an older copy method.
This calculator gives general estimates only and is not professional advice. Reviewed for general accuracy by Prof. Dr. Khalil Mudassar, PhD.