CSV to JSON for API Fixtures 日本語ガイド

CSV is often how sample data arrives. JSON is often how developers need to use it.

For API mocks, tests, and documentation, a header row usually maps well to JSON object keys:

id,name,active
1,Ada,true

[
  {
    "id": 1,
    "name": "Ada",
    "active": true
  }
]

Type inference is a choice

Turning "1" into 1 and "true" into true can be useful for fixtures. But it can be dangerous for:

• Account IDs with leading zeros
• ZIP or postal codes
• Large numeric identifiers
• Codes that look like numbers but are really strings

Disable type inference when exact text matters.

API fixture checklist

• Use stable header names that match the API contract.
• Keep row counts small for unit tests.
• Preserve strings when IDs or codes need exact formatting.
• Validate the final JSON with a formatter or schema when the payload matters.

Key takeaway

CSV → JSON is not just a format change. It is a schema decision: keys, types, nulls, and arrays should match the target API.

Use the CSV Converter with type inference on and off to compare fixture output.