How do I write multi-line strings in YAML correctly?

YAML provides two multi-line string syntaxes: the literal block scalar (|) which preserves newlines exactly, and the folded block scalar (>) which folds newlines into spaces for wrapping long strings. Use | for shell scripts, SQL queries, and configuration text where line breaks are meaningful, and > for long prose descriptions where you want to wrap lines in the YAML source without introducing actual newlines. Both styles support chomping indicators (+ to keep trailing newlines, - to strip them).

Can I convert between YAML and JSON without data loss?

Most YAML documents convert to JSON without data loss, but YAML supports features that have no JSON equivalent including comments, anchors and aliases for deduplication, multi-document streams separated by ---, and custom tags. These features are silently dropped or converted to their scalar representations during YAML-to-JSON conversion. JSON-to-YAML conversion is fully lossless since all JSON constructs map directly to YAML syntax.

Why does the YAML validator accept my file but my application rejects it?

Syntactically valid YAML may still fail application parsing because of schema restrictions — Kubernetes, for example, rejects YAML with duplicate keys or extra fields not in the resource schema even though they are syntactically valid. Type coercion differences also cause issues: a YAML boolean 'true' may be passed to a field that your application expects as the string 'true', causing a type error at the application layer rather than the parser layer. Validate against your application's specific schema after confirming basic YAML syntax.

What is the correct way to use tabs versus spaces in YAML?

The YAML specification forbids tab characters for indentation entirely — you must use spaces. Most editors that do not have YAML-specific configuration will silently insert tabs when you press the Tab key, creating files that look correct visually but fail to parse. Configure your editor to insert spaces (not tabs) for YAML files and enable whitespace visibility to see the difference. A consistent indentation width of 2 spaces is the most common convention in Kubernetes, GitHub Actions, and most YAML-based tooling.

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YAML Formatter

Format, validate, and convert YAML data. Clean syntax highlighting.

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Formatted YAML

How to Use

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Paste your YAML

Paste YAML content into the input area. The formatter handles nested mappings, sequences, anchors, aliases, and multi-line strings.

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Format and validate

Click Format to normalize indentation and spacing. Validation catches syntax errors like incorrect indentation, invalid characters, or duplicate keys.

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Copy formatted YAML

Click Copy to grab the clean YAML output. Ideal for reviewing Kubernetes manifests, CI/CD configs, Docker Compose files, or any YAML-based configuration.

What is YAML Formatter?

YAML Formatter is an online tool that validates and formats YAML files for correct syntax and consistent indentation, and converts between YAML and JSON formats bidirectionally. It solves the pain of debugging indentation-sensitive YAML configuration files where a single misaligned space causes cryptic parsing errors. DevOps engineers, backend developers, and platform engineers use YAML formatting constantly when working with Kubernetes manifests, GitHub Actions workflows, and Docker Compose files.

Why use YAML Formatter?

YAML's significant whitespace rules make it uniquely error-prone — the formatter catches mixed tabs and spaces, incorrect list indentation, and misaligned mapping keys that are invisible to the naked eye in most text editors. Bidirectional YAML-to-JSON conversion lets you paste YAML configuration into tools that expect JSON and vice versa without manually rewriting the structure. In-browser processing ensures Kubernetes secrets and CI/CD pipeline configurations containing credentials are never transmitted to a remote server.

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How it works

DevOps engineers paste GitHub Actions workflow YAML into the formatter to diagnose indentation errors that cause the workflow runner to fail with confusing step-skipping behavior rather than a clear syntax error. Platform engineers convert Helm chart values.yaml files to JSON for use with JSON Schema validators that enforce configuration contracts across deployment environments. Backend developers format OpenAPI specification files written in YAML to normalize indentation before committing to version control and running contract testing tools.

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Pro Tip

Never use tabs in YAML files — the spec technically allows them in some positions but most YAML parsers including those used by Kubernetes reject tab-indented content entirely, so always configure your editor to insert spaces for YAML file types. When converting between YAML and JSON, be aware that YAML supports a richer type system including custom tags and multi-line string literals that do not have a direct JSON equivalent and will be converted to their string representation.

Frequently Asked Questions

YAML's type inference is surprisingly aggressive — bare values like yes, no, true, false, on, off are all interpreted as booleans in YAML 1.1, and values like 1.0 or 1e3 are parsed as numbers. Country codes like 'NO' for Norway or port numbers like '8080' can be misinterpreted if not quoted. Always quote string values that could be confused with YAML scalars, and use the formatter to inspect the parsed type of ambiguous values before relying on them in code.

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