YAML Formatter & Validator

Clean and validate YAML for configs, Docker, and Kubernetes.

Privacy-first: your YAML never leaves your device. No uploads, no server. 100% client-side.

Format on paste, Ctrl+Enter to format, drag-drop .yaml/.yml/.txt (max 2MB). Autosave to localStorage.

IndentationIndentation:
Ctrl/Cmd + Enter · Runs in your browser
1 lines · 0 chars

Paste YAML and click Format YAML or press Ctrl+Enter. Formatted output will appear here.

YAML Formatting Examples

Badly formatted YAML

name:my-app
version: 1.0.0
env:production
ports:
-8080
-8443

Missing spaces after colons, inconsistent list style.

Correctly formatted output

name: my-app
version: 1.0.0
env: production
ports:
  - 8080
  - 8443

Consistent indentation (2 spaces), spaces after colons.

Kubernetes example

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  key: value

Manifests use 2-space indentation by convention.

Docker Compose example

services:
  web:
    image: nginx:alpine
    ports:
      - "80:80"
  app:
    build: .

Services and keys indented under services.

Why use a YAML formatter?

YAML is used everywhere: Kubernetes manifests, Docker Compose, GitHub Actions, Ansible, and CI/CD configs. Messy indentation or mixed styles make files hard to read and review. A formatter normalizes indentation (2 or 4 spaces), aligns key-value pairs, and keeps list items consistent so your configs are readable and version-control friendly.

This tool runs in your browser—no uploads, no server. Your YAML stays private. Use it alongside our JSON formatter and TOML formatter for a consistent workflow.

Common YAML mistakes

Indentation: YAML uses spaces, not tabs. Inconsistent indent (mixing 2 and 4 spaces) causes parse errors. Missing colons: Keys must be followed by a colon and a space (key: value). Lists: Use a consistent style—either - item with proper indent or inline [a, b]. Quotes: Unclosed or mixed quotes in strings break parsing. The validator highlights the line and column so you can fix quickly.

Use Validate YAML before applying configs to catch these issues in the browser with no upload.

YAML vs JSON

YAML is often used as a more readable alternative to JSON for config files: no quotes on keys, comments allowed, and multi-line strings are easier. Both represent the same tree of data. This tool can Copy as JSON so you can paste YAML-derived data into APIs or tools that expect JSON. Formatting and validation use the same parser logic so behavior is consistent.

For pure JSON workflows, use our JSON formatter; for YAML configs (Kubernetes, Docker, CI/CD), this formatter keeps everything client-side and private.

Kubernetes YAML formatting

Format Kubernetes manifests (Deployments, Services, ConfigMaps, Secrets) with consistent indentation. Paste your YAML and get clean, readable output that follows common style guides. Validation catches indentation and syntax errors before you apply with kubectl.

This YAML formatter online runs entirely in your browser—no uploads, so your cluster configs stay private. For other config formats, try our JSON formatter or TOML formatter.

Docker Compose YAML formatting

Clean up docker-compose.yml and Compose V2 YAML files. Fix indentation for services, volumes, and networks so your file is easy to read and version control.

Validate syntax before running docker compose up to avoid runtime errors.

CI/CD and config YAML

Format GitHub Actions, GitLab CI, CircleCI, and other CI/CD YAML configs. Pretty-print and validate workflow files so they are easier to review and debug. Supports multi-document YAML (documents separated by ---).

Privacy-first browser formatting means your pipelines and secrets never leave your machine. Explore more developer tools for formatting, validation, and encoding.

By Muhammad Abdullah Rauf · Founder, EverydayTools.proUpdated 2026-05-18

Quick answers

Concise answers for common searches — definitions, steps, and comparisons.

Why does kubectl fail on YAML that validates in a formatter?

YAML formatters check syntax (parseable structure). Kubernetes additionally validates against OpenAPI schemas per apiVersion/kind. A file can be valid YAML yet rejected because a field name is misspelled, a required field is missing, or a numeric field received a string. Workflow: validate syntax here → format for readable diffs → dry-run apply (kubectl apply -f file.yaml --dry-run=server) for schema. For pure config repos, add kubeconform or yaml-language-server schema association in CI.

What is the difference between YAML anchors and JSON there is no equivalent?

YAML anchors (&id) and aliases (*id) let one block be defined once and referenced multiple times in the same file — useful for repeating environment variables or volume mounts. The parser expands aliases before producing the final object tree. JSON has no anchor syntax; duplication must be explicit or handled by templating (Helm, Kustomize). Overuse of anchors hurts readability in git diffs — many teams prefer Helm charts or Kustomize patches instead of heavy anchor graphs.

How do you safely convert Kubernetes YAML to JSON for an API?

Parse YAML to a native object (Python yaml.safe_load, JavaScript yaml package with schema limits), then JSON.stringify the result. Never concatenate strings manually. Watch type coercion: unquoted yes/no may become booleans in YAML 1.1 parsers. Quote country codes and version strings. After conversion, validate JSON with a JSON validator before POSTing to admission webhooks or REST APIs that accept JSON-only bodies.

How to use YAML Formatter & Validator

  1. Paste your YAML

    Paste or type YAML content into the editor. The tool accepts any YAML — configuration files, data files, Kubernetes manifests, GitHub Actions workflows, Docker Compose files.

  2. Click Validate

    The validator runs a full YAML parse. If the YAML is invalid, it shows the error message with the line number and column position of the problem.

  3. Format the YAML

    Click Format to reindent the YAML with consistent 2-space indentation, add appropriate quoting, and normalise line endings. The formatted output is semantically identical to the input.

  4. Convert to JSON (optional)

    Use the YAML → JSON button to convert the parsed YAML to equivalent JSON. Useful for APIs that require JSON but configs are written in YAML.

Who uses YAML Formatter & Validator?

Common real-world scenarios where this tool saves time.

DevOps engineers

Validate Kubernetes, Docker Compose, and Helm charts

YAML syntax errors in Kubernetes manifests cause cryptic deployment failures. Validating before applying (kubectl apply) prevents common errors.

Developers working with CI/CD pipelines

Debug GitHub Actions and GitLab CI YAML

GitHub Actions workflows are YAML files where a single indentation error disables the entire pipeline. Validate workflow files before committing to catch errors immediately.

Configuration management teams

Standardise YAML formatting across a codebase

Format all configuration files to a consistent style before code review, making git diffs cleaner and reducing review friction caused by pure whitespace changes.

Workflow guides

Step-by-step chains that connect related tools for common tasks.

GitHub Actions workflow: validate → format → commit

  1. Paste workflow YAML here after editing — fix parse errors using line:column.
  2. Format for consistent 2-space indent before opening a PR.
  3. If a step outputs JSON env vars, validate embedded JSON fragments with JSON Validator in a separate paste.

K8s manifest triage: YAML → JSON → schema

  1. Format the manifest to see nesting of containers, env, and volumeMounts.
  2. Convert to JSON when debugging operators or admission webhooks that log JSON patches.
  3. Generate a schema from an example JSON export with JSON Schema Generator to document expected config shape for microservices.

YAML Formatter & Validator examples

Validate a Docker Compose file

Input

services:\n  web:\n    image: nginx\n  ports:\n    - '80:80'

Output

Error: Line 4 — 'ports' is indented under the root level, not under 'web'

YAML indentation errors are silent in some parsers but cause runtime failures. The validator flags the misalignment before the file is deployed.

Format a Kubernetes deployment manifest

Input

Unformatted YAML with inconsistent indentation

Output

Consistently indented YAML with 2-space nesting

Consistent indentation makes YAML readable and diff-friendly in git. The formatter normalises all indentation without changing the data structure.

When to use YAML Formatter & Validator vs related tools

Related toolUse this tool whenUse related tool when
JSON FormatterSource config is YAML (Actions, Helm values, docker-compose).Source is already JSON (package.json, API body).
JSON ValidatorValidating YAML syntax and indentation.Validating JSON converted from YAML or native JSON files.

Common mistakes to avoid

Indenting with tabs

YAML 1.2 forbids tab indentation. Configure the editor to insert spaces only (usually 2 per level for Kubernetes).

Unquoted * or & in plain scalars

These start aliases/anchors. Quote the value: "*" or use block scalars for multiline strings.

Assuming JSON tooling accepts YAML comments

Strip comments or use a YAML-aware parser before JSON.parse — comments are invalid in strict JSON.

Troubleshooting

did not find expected key at line N

Likely cause: Child key aligned with parent sibling instead of nested under parent.

Fix: Increase indent of child keys by exactly two spaces relative to the parent key line.

found character tab where indentation is expected

Likely cause: Tab character in margin.

Fix: Convert tabs to spaces across the file; many CI linters fail on tabs in YAML.

Kubernetes rejects valid-looking YAML

Likely cause: Schema validation failed — wrong apiVersion/kind or forbidden fields.

Fix: Syntax validation here only checks parseability. Run kubectl apply --dry-run=server or kubeconform for schema.

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Frequently Asked Questions

What are the most common YAML syntax errors?

1. Tabs instead of spaces — YAML requires spaces only. Tabs cause immediate parse failure. 2. Incorrect indentation depth — child nodes must be indented consistently relative to their parent. 3. Missing space after colon — key: value requires a space after the colon. 4. Unquoted special characters — strings starting with { [ @ | > : & * # ? must be quoted. 5. Duplicate keys — YAML allows them but parsers may ignore the second value silently.

Can YAML use tabs for indentation?

No. YAML explicitly prohibits tab characters for indentation. This is a deliberate design choice to avoid the ambiguity of tab width interpretation. If a YAML file uses tabs, it will fail to parse. Configure your editor to use spaces (not tabs) for YAML files.

What is the difference between YAML and JSON?

JSON is a strict subset of YAML 1.2 — all valid JSON is valid YAML. YAML adds: comments (#), multi-line strings (| and > operators), anchors and aliases for reuse (&anchor, *alias), and less punctuation (no double-quotes required for most strings). YAML is preferred for human-edited configs; JSON for machine-to-machine APIs.

Why does YAML sometimes interpret numbers and booleans unexpectedly?

YAML 1.1 (older parsers) treats yes/no/on/off/true/false as booleans and 0o744 as octal. This causes bugs when these values are meant as strings (e.g. a country code 'NO' being interpreted as false). YAML 1.2 fixed most of these. Always quote values that should be strings: 'yes', 'no', 'true', '0744'.

Related Tools

More free tools for the same workflow.

TOML Formatter

Format and validate TOML config files like Cargo.toml and pyproject.toml instantly in your browser. Syntax highlighting, error detection, no upload required.

JSON Schema Generator

Free JSON Schema generator — paste sample JSON and instantly generate a JSON Schema Draft-7 with inferred types, required fields, and nested object definitions. No signup.

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Reviewed by EverydayTools Editorial Team.