Does YAML indentation require spaces?

Yes, the YAML specification strictly forbids using tabs for indentation. All indentation levels must consist of one or more spaces. This tool automatically detects illegal characters to help you troubleshoot parse failures caused by tab characters.

Does YAML support comments?

Yes. YAML uses a hash sign (#) at the start of a line for comments — this is one of its key advantages over JSON and makes it excellent as a configuration file format.

How do I handle multi-line strings?

YAML provides the pipe symbol (|) to preserve newlines and the greater-than symbol (>) to fold newlines. These are particularly useful when defining Kubernetes ConfigMaps or script blocks.

Can JSON and YAML be converted between each other?

In theory, JSON is a subset of YAML, so all valid JSON is also valid YAML. This tool supports converting complex YAML objects to formatted JSON, and vice versa (you can paste JSON directly into the input to achieve JSON-to-YAML conversion).

What implicit type coercion pitfalls exist in YAML?

YAML 1.1 (still the default for most parsers including js-yaml) automatically coerces yes/no/on/off to boolean true/false, date-like strings (2024-01-15) to Date objects, and 0-prefixed numbers to octal. This causes surprising failures in Kubernetes configs, GitHub Actions branch name comparisons, and version string handling. Fix with explicit quoting: port: "8080", branch: "on". YAML 1.2 resolved most of this, but parser defaults are slow to change.

How do you safely represent strings with special characters in YAML?

When a string contains colons, hash signs, brackets, or braces, wrap it in quotes. Single-quoted strings are fully literal with no escape processing; double-quoted strings support backslash escape sequences for newlines and tabs. Key rule: a bare colon followed by a space is always parsed as a key-value separator — any string containing this pattern must be quoted. Example: nginx:1.24 is safe (no space after the colon), but on: on must be written as on: "on" to prevent boolean coercion.

What is the YAML multi-document separator (---) and when should you use it?

YAML supports multiple documents in a single file, separated by three dashes (---) and optionally ended with three dots (...). This is standard in Kubernetes, where a single .yaml file holds a Deployment, Service, and ConfigMap together, all applied at once via kubectl apply -f. GitHub Actions workflow files conventionally begin with --- to mark the document start. This tool validates single-document YAML; for multi-document files, validate each section individually.

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YAML Validator

Real-time YAML syntax validation, YAML ↔ JSON conversion, and syntax highlighting.

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YAML Input

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Enter YAML on the left to see the result here

What is the YAML Validator?

YAML (YAML Ain't Markup Language) is a human-friendly data serialization standard widely used for configuration files (Kubernetes, Docker Compose, GitHub Actions, etc.). While YAML is more readable than JSON, its strict indentation rules frequently cause syntax errors that are difficult to spot by eye.

This tool provides real-time YAML syntax checking with precise error location. It also supports converting YAML to standard JSON format, making it easy to debug data across different systems. All processing happens locally in your browser, ensuring your configuration data remains private and secure.

How to use this tool

Paste or write your YAML content in the left editing area. The status bar gives instant feedback on whether the syntax is valid, with specific error descriptions if not. Click "Load Example" to see a standard YAML structure.

When the YAML is valid, you can switch the output mode between "YAML" and "JSON". The right panel displays the result with syntax highlighting based on your selection. Click "Copy Result" to save the processed content to your clipboard in one click.

Typical Production Scenarios

Kubernetes Resource Config Debugging

Before running kubectl apply, paste Deployment, Service, or Ingress YAML here to catch syntax errors early. Indentation errors cause kubectl to report "mapping values are not allowed," while field name typos only surface after apply via kubectl describe. This tool catches syntax-layer issues before you commit the change.

Docker Compose File Check

Validate indentation and field structure in compose.yml service definitions. Common errors include inconsistent indentation in ports and volumes lists, wrong nesting depth in environment blocks, and depends_on formats that do not conform to Compose v2/v3 spec. Paste the content here to catch these issues before running docker compose up.

GitHub Actions Workflow Validation

Workflow file (.github/workflows/*.yml) syntax errors only surface on the GitHub UI after a push triggers the job — making for slow debug cycles. Pasting the workflow here validates the basic YAML structure and lets you confirm that jobs/steps indentation is correct before the CI pipeline is triggered.

Helm values.yaml Syntax Check

Before helm install or helm upgrade, validate the YAML syntax of values.yaml. One common root cause of Helm rendering errors is indentation mistakes or unquoted values that trigger YAML type coercion (for example, boolean-like strings not wrapped in quotes). Confirm the YAML is valid here before running helm template.

YAML Common Pitfalls

Tab vs Space Indentation: YAML completely forbids tab characters for indentation. When pasting YAML from an editor with auto-indent conversion disabled, tab characters are easily introduced, causing the parser to fail with "found a tab character where an indentation space is expected." Set your IDE to enforce space-only indentation for .yaml/.yml files (VS Code: editor.insertSpaces: true) to prevent this at the source.

Implicit Type Coercion: YAML auto type inference frequently produces surprises in config contexts. Boolean-like values (yes/no/on/off/true/false) are parsed as Boolean, which breaks Ansible playbooks and Docker Compose condition fields. Numbers prefixed with 0 may be parsed as octal, and date-format strings (2024-01-15) become Date objects rather than strings. Always quote values that could trigger inference: on: "on", version: "1.0".

Anchor and Alias Merge Pitfalls: YAML anchors (&name) and aliases (*name) with merge keys (<< : *base) have subtle behavior — keys defined after the merge override the anchored values, which is the opposite of what many developers expect. Additionally, libraries like js-yaml expand all alias references on serialization, potentially inflating the output size significantly. For production config files, prefer explicit repetition over anchors to ensure compatibility across the toolchain.

Convert YAML to JSON Online

Converting YAML to JSON is one of the most frequent debugging needs: many APIs, logging systems, and frontends only accept JSON, while configuration is authored in YAML. This tool includes a built-in online YAML to JSON converter — once validation passes, switch the output mode to JSON to get standard, syntax-highlighted, copy-ready JSON, with no need to install yq or write a throwaway python -c "import yaml,json" script.

Be aware of what changes during conversion: YAML comments are lost when converting to JSON because JSON has no comment syntax; anchors and aliases are expanded into full repeated content; and YAML block scalars (the literal and folded styles) are collapsed into single-line JSON strings with escaped newlines. The reverse JSON-to-YAML conversion is always lossless, since JSON is a strict subset of YAML.

Why Use an Online YAML Validator

The biggest advantage of an online YAML validator is zero environment setup: validating locally with yamllint requires installing Python and a pip package, and IDE plugins are tied to a specific editor. A free online YAML validator only needs a browser, making it ideal for quickly triaging CI failures, double-checking config on a production bastion host, or working on a colleague's machine that has no dev environment.

Compared with command-line tools, this online validator adds instant visual feedback: validate-as-you-type, line-and-column error locations, syntax highlighting, and one-click YAML-to-JSON comparison. And because it runs entirely in your browser, it combines the convenience of an online tool with the privacy of a local one — your config data never leaves your machine.