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The YAML to JSON tool converts YAML (YAML Ain’t Markup Language) documents into JSON format. It handles both single-document and multi-document YAML files, making it essential for working with configuration files, CI/CD pipelines, and data interchange.

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Use Cases

  • Converting Kubernetes manifests to JSON for programmatic processing
  • Transforming CI/CD configs (GitHub Actions, GitLab CI) to JSON
  • Parsing YAML config files for API consumption
  • Validating YAML syntax by converting to JSON
  • Processing multi-document YAML (e.g., Kubernetes resources with --- separators)
  • Data interchange between YAML-based and JSON-based systems

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How It Works

The tool uses the js-yaml library to parse YAML syntax and convert it to JavaScript objects, then serializes to JSON:
  1. Parse YAML using yamlLoadAll() (supports multi-document)
  2. Detect document count:
    • Single document → Output single JSON object
    • Multiple documents → Output JSON array of objects
  3. Serialize to JSON with 2-space indentation
The tool automatically detects multi-document YAML (documents separated by ---) and outputs a JSON array when multiple documents are found.

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Input Format

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Single-Document YAML

name: John Doe
age: 30
address:
  street: 123 Main St
  city: New York
  zip: "10001"
hobby:
  - reading
  - hiking
  - coding

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Multi-Document YAML

---
kind: Deployment
metadata:
  name: app-deployment
spec:
  replicas: 3
---
kind: Service
metadata:
  name: app-service
spec:
  type: ClusterIP
  ports:
    - port: 80

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Output Format

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Single Document → JSON Object

{
  "name": "John Doe",
  "age": 30,
  "address": {
    "street": "123 Main St",
    "city": "New York",
    "zip": "10001"
  },
  "hobby": [
    "reading",
    "hiking",
    "coding"
  ]
}

​
Multiple Documents → JSON Array

[
  {
    "kind": "Deployment",
    "metadata": {
      "name": "app-deployment"
    },
    "spec": {
      "replicas": 3
    }
  },
  {
    "kind": "Service",
    "metadata": {
      "name": "app-service"
    },
    "spec": {
      "type": "ClusterIP",
      "ports": [
        { "port": 80 }
      ]
    }
  }
]

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Examples

Input:
app:
  name: MyApp
  version: 1.2.3
  debug: true
  features:
    - auth
    - api
    - admin

Output:
{
  "app": {
    "name": "MyApp",
    "version": "1.2.3",
    "debug": true,
    "features": ["auth", "api", "admin"]
  }
}

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Technical Details

Located in lib/tools/engine.ts:497-501
The tool uses js-yaml (YAML 1.2 parser): 
import { loadAll as yamlLoadAll } from 'js-yaml';

const docs = yamlLoadAll(input);
if (docs.length === 1) {
  return { output: JSON.stringify(docs[0], null, 2) };
}
return { output: JSON.stringify(docs, null, 2) };

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YAML Features Supported

  • Scalars: strings, numbers, booleans, null
  • Collections: sequences (arrays), mappings (objects)
  • Multi-line strings: literal (|) and folded (>) blocks
  • Anchors and aliases: &anchor and *alias references
  • Comments: Parsed but not preserved in JSON output
  • Multi-document files: Separated by ---

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Type Conversion

YAMLJSON
true, false, yes, notrue, false
123, 0x1A, 0o17123 (decimal)
1.23, 1.23e4, .inf1.23, 12300, null
null, ~null
"quoted", unquoted"string"
2024-03-04"2024-03-04" (string)
YAML date objects (e.g., 2024-03-04) are converted to ISO 8601 strings in JSON, not Date objects. YAML binary data (!!binary) is converted to base64 strings.

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YAML Syntax Tips

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Preserving Numeric Strings

Quote numbers that should remain strings: 
zip_code: "10001"  # String, not number
port: 8080         # Number

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Multi-line Strings

# Literal block (preserves newlines)
description: |
  Line 1
  Line 2
  Line 3

# Folded block (collapses newlines to spaces)
summary: >
  This is a long
  sentence that will
  be on one line.

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Anchors and Aliases

defaults: &defaults
  timeout: 30
  retries: 3

service1:
  <<: *defaults
  name: Service 1

service2:
  <<: *defaults
  name: Service 2
Converts to: 
{
  "defaults": {"timeout": 30, "retries": 3},
  "service1": {"timeout": 30, "retries": 3, "name": "Service 1"},
  "service2": {"timeout": 30, "retries": 3, "name": "Service 2"}
}

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Common Errors

YAML is indentation-sensitive (like Python). Use consistent spaces (2 or 4) for indentation. Do not mix tabs and spaces.
# ❌ Incorrect (mixed indentation)
parent:
    child: value

# ✅ Correct (consistent 2-space indentation)
parent:
  child: value
Ensure colons (:) are followed by a space:
# ❌ Incorrect (no space after colon)
key:value

# ✅ Correct
key: value
The separator --- must be on its own line:
# ❌ Incorrect
doc1: value ---
doc2: value

# ✅ Correct
doc1: value
---
doc2: value

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