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YAML Formatter & Validator

Format, validate and convert YAML instantly

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🔒 No upload — runs entirely in your browser. Your data never leaves your device.

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What is the YAML Formatter?

The YAML Formatter parses any YAML document and rewrites it with consistent 2-space indentation, standardized spacing, and normalized structure — then validates it for syntax errors at the same time. It also converts between YAML and JSON in both directions, which is essential when you need to pass YAML configuration data to a JavaScript function, REST API, or tool that only accepts JSON.

YAML (YAML Ain't Markup Language) is the dominant format for human-edited configuration files: Kubernetes manifests, Docker Compose files, GitHub Actions workflows, CircleCI pipelines, Ansible playbooks, Helm chart values, and application config files in Ruby on Rails, Symfony, and many other frameworks all use YAML. Because YAML relies on indentation — rather than delimiters like curly braces — for structure, a single misaligned line silently breaks the entire file. The formatter catches these problems before they reach your deployment pipeline.

Everything runs entirely in your browser. Your YAML content — which often contains database connection strings, API keys, Kubernetes secrets, and other sensitive configuration — is never transmitted to any server. You can safely paste production config files without any data leaving your device.

How to Use the YAML Formatter

  1. 1.Choose a mode: Format to pretty-print and reindent, Validate to check syntax without changing the document, YAML → JSON to convert to JSON, or JSON → YAML to convert from JSON.
  2. 2.Paste your YAML (or JSON, in JSON → YAML mode) into the left panel. The formatter processes it automatically as you type.
  3. 3.If the input is invalid, a red error panel shows the exact syntax error description, which typically pinpoints the problematic line and the nature of the issue.
  4. 4.Click Copy in the output panel header to copy the formatted result to your clipboard.
  5. 5.Use Load Sample to insert an example YAML document if you want to explore the tool before pasting your own data.

Example: copy a Kubernetes Deployment manifest from your terminal with kubectl get deployment myapp -o yaml, paste it here, and click Format to normalize the indentation before adding it to your Git repository.

YAML vs. JSON: Key Differences

YAML and JSON represent the same underlying data model — objects (key-value maps), arrays, strings, numbers, booleans, and null — but they look and behave quite differently in practice.

Syntax. JSON uses curly braces for objects, square brackets for arrays, commas to separate items, and double quotes around all keys and string values. YAML uses indentation for nesting, dashes for list items, and colons to separate keys from values. Most string values do not need quotes in YAML unless they contain special characters. This makes YAML significantly more readable for complex, deeply nested configuration.

Comments. JSON has no comment syntax. YAML supports comments starting with #, which is why configuration files favor YAML — you can document why a value is set without hacking it into a dummy key. When you convert YAML to JSON with this tool, comments are dropped since JSON cannot represent them.

Type coercion. YAML performs implicit type conversion. The value true, yes, on, and True all parse as boolean true. The value 0755 parses as an octal integer. Bare strings that look like numbers parse as numbers. This convenience can cause surprising bugs — for example, country codes like NO (Norway) parse as boolean false in YAML 1.1. Quoting the value prevents implicit conversion.

Multi-document files. A single YAML file can contain multiple independent documents separated by ---. Kubernetes manifests often use this to bundle multiple resources (a Deployment and a Service) in one file. JSON has no equivalent — each JSON file contains exactly one value.

Common YAML Syntax Errors and How to Fix Them

The validator shows the exact error from the YAML parser. Here are the most frequent errors and how to resolve them.

  • Tabs in indentation.YAML strictly forbids tab characters for indentation — only spaces are allowed. If your editor inserts tabs, the parser throws immediately. Replace all tabs with the appropriate number of spaces. Most editors have a "convert tabs to spaces" setting; set it globally for YAML files.
  • Inconsistent indentation. Each level of nesting must add the same number of spaces throughout the document. If you use 2 spaces at one level and 4 at another, the parser misinterprets the hierarchy. Paste into this formatter and click Format to automatically normalize to 2-space indentation.
  • Missing space after colon. key:value is invalid; it must be key: value with a space. The exception is inside a flow mapping ({key: value}) where the colon-space rule still applies.
  • Unquoted special characters. Values that start with :, {, [, #, |, >, *, &, or ! must be quoted: url: "https://example.com".
  • Incorrect multi-line string syntax. YAML has two block scalar indicators: | (literal, preserves newlines) and > (folded, folds newlines to spaces). The content must be indented by at least one more space than the key, and the indentation must be consistent throughout the block.
  • Duplicate keys. YAML technically allows duplicate keys but most parsers either error or silently keep the last value. Always use unique keys within a mapping. Helm chart values and Kubernetes annotations are frequent sources of accidental duplicate keys when merging templates.

YAML in Kubernetes, Docker Compose, and CI/CD Pipelines

Kubernetes, the container orchestration platform used by most production cloud applications, uses YAML for all of its configuration objects: Deployments, Services, ConfigMaps, Secrets, Ingresses, PersistentVolumeClaims, and more. A typical production cluster might have hundreds of YAML manifests, each needing consistent formatting and strict syntax validity. A single indentation error in a Kubernetes manifest causes kubectl apply to fail with an opaque error, often without pointing directly to the line that caused the problem. Formatting your manifests before applying them prevents this class of deployment failure entirely.

Docker Compose uses a YAML file (docker-compose.yml or compose.yaml) to define multi-container applications. Services, volumes, networks, and environment variables are all specified in YAML. Unlike Kubernetes, Docker Compose provides reasonably clear error messages, but formatting first helps when sharing Compose files across a team with different editor configurations.

GitHub Actions workflow files (.github/workflows/*.yml) define CI/CD pipelines entirely in YAML. A syntax error in a workflow file silently prevents the workflow from running at all — GitHub just shows a yellow warning icon in the Actions tab without a clear error. Validating workflow files locally before pushing saves the round-trip of discovering the error after a commit.

Ansible playbooks, Helm chart values files (values.yaml), OpenAPI 3.0 specifications, and AWS CloudFormation templates in YAML format all benefit from the same formatting and validation workflow.

Best Practices for Writing YAML Configuration Files

A few habits make YAML files easier to maintain across a team and less likely to cause unexpected behavior.

Use 2-space indentation consistently. Two spaces is the de facto standard for YAML, used by Kubernetes, GitHub Actions, and most YAML generators. Four spaces or mixed indentation works technically but introduces friction when merging files or running them through automated generators.

Quote values that could be misinterpreted. Country codes (NO, YES, ON, OFF), octal-looking numbers like file permissions (0755), version strings like 1.0, and empty strings should always be quoted to prevent implicit type coercion.

Use comments liberally. Unlike JSON, YAML supports # comments. Document what each key does, why a value was chosen, and any environment-specific overrides that future maintainers need to know about. This context would be lost in a JSON config.

Avoid anchors and aliases in files shared across tools. YAML anchors (&anchor_name) and aliases (*anchor_name) let you reference one value from multiple places. While they reduce duplication, they are not supported by all YAML parsers (Kubernetes ignores them, for example) and make files harder to read at a glance.

Validate before committing. Add a YAML linting step to your CI pipeline (yamllint or prettier --check) so that malformed YAML is caught automatically on every pull request. For quick one-off validation during development, this formatter is the fastest option.

Worked Example: Formatting a Kubernetes Deployment

Here is a realistic before-and-after example of what the YAML formatter does. Suppose a developer copies a Kubernetes Deployment manifest from a web tutorial and pastes it into their repository. The tutorial used 4-space indentation, but the rest of their manifests use 2-space. The formatter normalizes the indentation in one click.

Before formatting (4-space, inconsistent):

apiVersion: apps/v1
kind: Deployment
metadata:
    name: my-app
    labels:
        app: my-app
spec:
    replicas: 3
    selector:
        matchLabels:
            app: my-app
    template:
        metadata:
            labels:
                app: my-app
        spec:
            containers:
            - name: my-app
              image: my-app:1.0.0

After clicking Format (2-space, consistent):

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
  labels:
    app: my-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
        - name: my-app
          image: my-app:1.0.0

The data is identical — only the indentation changed. Running kubectl apply -f deployment.yaml accepts both, but the 2-space version is consistent with the rest of the project and passes automated YAML linting checks without configuration overrides. You can also click YAML → JSON on this same manifest to get a JSON representation that you can pass to the Kubernetes API directly via kubectl apply --server-side -f - or use in a JavaScript program that calls the Kubernetes API with the official client library, which expects JSON rather than YAML.

Frequently Asked Questions

What is a YAML formatter?+
A YAML formatter parses a YAML document and rewrites it with consistent indentation, standardized spacing around colons and dashes, and normalized quoting. It also validates the document against YAML syntax rules and reports the exact line and description of any errors. Use it to clean up inconsistently indented config files, spot typos before deploying to Kubernetes or CI/CD pipelines, and convert YAML to JSON for use in APIs or JavaScript applications.
What is the difference between YAML and JSON?+
YAML (YAML Ain't Markup Language) and JSON (JavaScript Object Notation) represent the same kinds of data — objects, arrays, strings, numbers, booleans, and null — but with different syntax. YAML uses indentation and newlines to define structure, supports comments with #, and does not require quotes for most strings. JSON uses curly braces, square brackets, and commas, requires all strings to be double-quoted, and has no comment syntax. YAML is more readable for human-edited configuration files; JSON is more compact and universally supported by programming languages and APIs. The two formats are interconvertible, which is why this tool includes YAML-to-JSON and JSON-to-YAML conversion.
How do I fix a YAML indentation error?+
YAML uses indentation to define hierarchy, and indentation must be consistent within a file — either always 2 spaces or always 4 spaces; tabs are not allowed. When the formatter reports an indentation error, look at the flagged line and verify that its indentation is a multiple of the indentation unit used by the file. Common causes are: mixing tabs and spaces (use only spaces), inconsistent levels (a child key indented 3 spaces when the parent uses 2-space increments), and block scalar content accidentally unindented. Paste your YAML into this formatter and click Format to automatically reindent the document with consistent 2-space indentation.
How do I convert YAML to JSON?+
Paste your YAML into the input panel and click the "YAML → JSON" button. The tool parses the YAML and outputs the equivalent JSON with 2-space indentation. All YAML data types map to their JSON equivalents: YAML strings become JSON strings, YAML integers and floats become JSON numbers, YAML booleans (true/false/yes/no/on/off) become JSON booleans, YAML null/~ becomes JSON null, YAML sequences become JSON arrays, and YAML mappings become JSON objects. Note that YAML comments are dropped during conversion since JSON has no comment syntax.
What are the most common YAML syntax errors?+
The most frequent YAML syntax errors are: (1) tabs instead of spaces — YAML forbids tab characters for indentation; replace all tabs with spaces; (2) inconsistent indentation — each level must add the same number of spaces throughout the file; (3) missing space after a colon — key: value requires a space after the colon, except inside quoted strings; (4) unquoted special characters — values starting with %, @, `, |, >, or & should be quoted or escaped; (5) duplicate keys — YAML allows duplicate keys but parsers typically warn or error; (6) incorrect block scalar indentation — literal (|) and folded (>) block scalars require their content to be indented relative to the indicator; (7) unmatched flow indicators — every { must have a matching } and every [ must have a matching ].
Does this YAML formatter work with Kubernetes, Docker Compose, and GitHub Actions files?+
Yes. Kubernetes manifests, Docker Compose files, GitHub Actions workflows, CircleCI configs, Ansible playbooks, and Helm chart values are all standard YAML and are fully supported by this formatter. You can paste a Kubernetes Deployment or Service manifest, a docker-compose.yml, or a .github/workflows/*.yml file into the input panel and click Format to reindent it consistently or Validate to check for syntax errors before committing. The formatter handles multi-document YAML (files with --- separators) correctly.
Is my YAML data safe when using this tool?+
Yes. The YAML Formatter on Nutilz runs entirely in your browser using JavaScript. Your YAML content — which may include API keys, database passwords, Kubernetes secrets, or other sensitive configuration — is never sent to any server. All parsing, formatting, validation, and conversion happens locally in your browser. Once you close the tab, nothing is stored. This makes it safe to use with production configuration files that contain credentials.