YAML Validator will check your YAML syntax instantly, live as you type. Get the exact line and column of any error. No uploads, no storage, no tracking — your data stays in your browser.
Validation Result
✔Valid YAML
Lines: 0Characters: 0Documents: 0
Table of Contents
What Is YAML?
YAML, which stands for “YAML Ain’t Markup Language,” is a way to serialize data that is readable by humans. It was intended to be accessible to the human reader as well as easily interpreted by computers. Instead of braces and brackets, which JSON uses, and opening and closing tags used by XML, configuration files written in YAML are often dramatically shorter and easier to scan due to the use of plain indentation to express structure.
Today YAML is the default language of the DevOps world. YAML is the language used for Kubernetes manifests, Docker Compose files, Ansible playbooks, GitHub Actions workflows, GitLab CI pipelines, Helm charts, and OpenAPI specs. This can be used for comments, multi-line strings, references to reused values (anchors) and multiple documents within a single text file separated by the special separator “—“. The complete grammar is specified in the official YAML specification and is the authoritative source for what is and is not a valid YAML.
When Do You Need a YAML Validator?
Always have a YAML syntax checker handy when you get a configuration that won’t apply and the error message doesn’t point anywhere. The Kubernetes cluster will be happy to tell you a manifest is invalid and not reference the extra tab at line 47. Editors help, but if the issue is not in the editor but in the file, then having a file going to a validator gives you an independent and parser-accurate verdict, which comes in handy when you are reviewing another person’s pull-request and don’t have the tooling easily available.
Why Use Our YAML Validator?
YAML appears to be straightforward, and it is! Just a single extra space, tab or un-quoted value might silently alter the meaning of an entire configuration file. If that file is a Kubernetes manifest, a Docker Compose stack or a CI/CD pipeline, then the error becomes apparent during deployment. Our free YAML validator helps with that – it can detect those issues at a glance online.
This tool validates live as you type, unlike most YAML checkers that require pasting your content and click a button. Each keystroke is re-parsed instantly, and a single error provides you with the exact line and column location of the error, as well as a small portion of the offending line, to help you immediately see which line and column contains the error. If every’s correct, a clear green indicates that your YAML is valid. Your configuration files, typically containing internal hostnames, environment names and more that you might not want to be uploaded to any server, are not uploaded to any server at all with the tool!
How to Use the YAML Validator
Type or paste your YAML into the left-hand text box.
Observe the result panel on the right: the validation is automatic and takes place each time the result is changed (without pressing a button).
If the YAML is not valid, the panel turns red, and displays the line number, column, parser message, and the text of the failed line with a caret indicating the error.
If your syntax is correct, the panel switches back to green.
Load Sample to view a valid Kubernetes deployment or Load Broken Example to view errors reported. The numbers below the result show the number of characters, documents and lines that you are tracking.
Most Common YAML Errors
Almost every YAML failure traces back to a handful of recurring mistakes. Knowing them saves hours of debugging:
Error
What Happens
Fix
Tab characters
YAML forbids tabs for indentation — parsers reject the file outright.
Configure your editor to insert spaces (2 is the convention).
Inconsistent indentation
Mixing 2-space and 4-space nesting shifts keys to the wrong level or breaks parsing.
Pick one indent size per file and apply it everywhere.
Colon in a value
time: 12:30 splits the value unexpectedly because : starts a new mapping.
Quote the value: time: "12:30".
Unquoted booleans
In YAML 1.1, yes, no, on, and off parse as true/false, not strings.
Quote them when you mean text: "no".
Missing space after colon
key:value is read as a plain string, not a key-value pair.
Always write key: value with a space.
Duplicate keys
The same key twice in one mapping — one value silently wins.
Merge the entries or rename one key.
YAML vs JSON: What to Use?
YAML actually is a superset of JSON — every valid JSON is also a valid YAML — so they have many similarities. It is more strict and efficient to parse than XML so is more suitable for APIs and machine-to-machine data transfer. YAML relaxes that strictness in favor of readability: comments, more tidy nesting, and multi-line strings mean it is the more human-readable file format to work with by hand. The basic rule that most teams follow is to make configuration files in YAML, and exchange data in JSON. Because YAML’s readability is achieved through indentation, a YAML lint tool such as this is the safety net that ensures hand-edited files are kept honest.
FAQs
Is this YAML validator really free?
Yes. There is no sign up, no file size limits imposed by us, no caps placed on usage – it is 100% free. All operations are done in your browser.
Do I have my YAML file deployed to a server?
No. JavaScript YAML parser is used within your browser to validate. All that you paste is not sent, logged, stored — even internal information is safe in configuration files.
What is the difference between a YAML validator and a YAML linter?
A validator validates the correctness of your YAML: syntactic correctness, that your YAML can be used by a parser. A linter takes it further and applies style rules such as consistency of the size of the indentation or removal of trailing spaces. This tool is just for syntax validation, a file may be correct YAML but still have problems with respect to a team’s style guide.
My YAML is valid but Kubernetes rejects it. Why?
Syntax validity and schema validity are different things. You can have a perfectly well parseable YAML file that lacks field(s) that Kubernetes expects, like apiVersion or kind, or has a field name that it does not recognize. This validator checks the syntax, the error message by the API server details the schema.
Is it possible to validate more than one YAML document in a file?
Yes. A group of documents separated by lines of — are read together. In the stats area, it displays the number of documents it has found, and if there is any error, it displays the line and column.
Why not allow tabs in YAML to be used for indentation?
The specification did not include tabs, as they are displayed at different widths in different editors and would make it ambiguous what structure a file has. Indentation is always what it means, and the spaces are always the same width.
