YAML Formatter & JSON Converter — Format YAML Free in Your Browser

YAML is the configuration language of modern infrastructure — Kubernetes manifests, Docker Compose files, GitHub Actions workflows, Ansible playbooks, and countless application configs. SimpleTools YAML Formatter formats, validates, and converts YAML to/from JSON, entirely in your browser.

What the YAML Formatter Does

Validation: Checks YAML syntax and reports errors with line numbers — a missing colon, incorrect indentation, or invalid YAML construct is caught immediately.

Formatting: Normalises indentation, quote styles, and multi-line string formatting to produce consistent, readable YAML.

YAML → JSON conversion: Convert YAML configuration to equivalent JSON — useful for APIs that accept JSON, for debugging, or for developers more comfortable with JSON.

JSON → YAML conversion: Convert JSON back to YAML — cleaner, more readable for configuration management.

Before and After: YAML Formatting

Before:

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

After formatting:

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

Consistent 2-space indentation, no extra spaces after colons, properly aligned nesting.

YAML Validation Rules

YAML has strict indentation rules and a few common pitfalls:

1. Indentation matters: YAML uses spaces (not tabs) for structure — mixing causes parse errors
2. Colon + space: key: value — the space after the colon is required
3. String quoting: Values starting with special characters ({, [, :, #) need quoting
4. Multi-line strings: | for literal blocks, > for folded blocks — easy to mix up
5. Boolean trap: yes, no, on, off, true, false are all YAML booleans — quote them if you mean strings
6. Tabs forbidden: YAML does not allow tab characters for indentation

Features

• Syntax validation: Real-time validation with line/column error positions
• Format/beautify: Consistent indentation and normalised formatting
• YAML → JSON: Convert YAML to formatted JSON
• JSON → YAML: Convert JSON to clean YAML
• Minify YAML: Compact output for embedding in scripts or CLI commands
• Highlight mode: Syntax highlighting for keys, values, comments, and anchors
• Anchor/alias support: Handles &anchor and *alias YAML features
• Multi-document YAML: Handles --- document separators

Why Process Config Files in Your Browser?

YAML configuration files often contain:

• Database connection strings with credentials
• API keys and secrets embedded in config
• Infrastructure topology revealing internal architecture
• Kubernetes secrets (though these should be managed by a secrets manager)
• CI/CD pipeline logic revealing deployment processes

Sending these to a cloud-based YAML tool is an unnecessary security risk.

SimpleTools YAML Formatter:

✅ Your YAML never leaves your browser
✅ Works offline — format configs without internet
✅ No account or API key needed
✅ Free for files of any size

How It Works

The tool uses js-yaml — the most widely-used JavaScript YAML parsing library:

import yaml from 'js-yaml';

// Parse YAML to JavaScript object
const parsed = yaml.load(yamlString);

// Convert to JSON
const json = JSON.stringify(parsed, null, 2);

// Convert back to YAML
const reformatted = yaml.dump(parsed, { indent: 2 });

The yaml.load() function validates and parses the YAML. Any syntax error throws an exception with a line/column reference. The yaml.dump() function re-serialises the parsed object to normalised YAML.

How to Use the YAML Formatter

1. Visit simpletools.one/yaml-formatter
2. Paste your YAML in the input panel
3. Validation errors appear immediately in the error panel
4. Click Format to normalise the YAML
5. Click → JSON to convert to JSON
6. Click → YAML (in JSON mode) to convert back to YAML
7. Click Copy or Download to save the result

Common YAML Errors and Fixes

Use Cases

• Kubernetes YAML: Validate manifests before applying with kubectl apply
• Docker Compose: Format and validate docker-compose.yml before deploying
• GitHub Actions: Debug workflow YAML indentation issues
• Ansible: Validate playbooks and role files
• Application config: Format and check app config files (config.yaml, settings.yml)
• API testing: Convert between YAML test data and JSON request bodies

Format and validate your YAML at simpletools.one/yaml-formatter — private, instant, and completely free.