CSV to JSON Converter

CSV is a general-purpose table format, but in many modern development scenarios, JSON is the data format of choice:

• API development: Communication protocols such as RESTful API, GraphQL, and WebSocket all use JSON as the standard format. CSV needs to be converted to JSON before importing it into the API.
• NoSQL database: MongoDB, Firebase, etc. use JSON files, and CSV needs to be converted before importing.
• JavaScript / TypeScript： Front-end and Node.js projects natively support JSON, which can be directly import or JSON.parse()。
• Python data science: Pandas can read CSV, but many API responses with ML model input require JSON.
• AI/LLM workflow: AI model training data, prompt templates, and Function Calling structure definitions usually use JSON.

CSV is essentially all text, but JSON supports multiple data types. Autotype determination identifies the best type for each value:

name,age,active,score
Gary,30,true,95.5

{
  "name": "Gary",
  "age": 30,
  "active": true,
  "score": 95.5
}

Conversion rules:

• "true" / "false" → Bollinger value
• "30"、"95.5"、"-5" → numbers
• "null" → null
• Null value → According to the set null value processing method
• The rest → String

💡 Select the "Treat all as string" mode to retain the original text in the CSV without any type conversion.

When the CSV field name contains a period (e.g. profile.age、address.city), Nested Object mode will automatically expand them into nested JSON objects:

profile.age,profile.city 30,Taipei

{ "profile": { "age": 30, "city": "Taipei" } }

Comparison of three output modes:

• Object Array — One object for each piece of data, forming an array. The most versatile preset mode.
• Key-Value Object — Use the specified field as the Key and the entire data as the Value to output an entire object.
• Nested Object — Automatically expand point notation fields into multi-layered nested objects.

💡 When a dot notation field is detected, a blue prompt will be displayed at the top of the tool: "Nested field detected (dot notation)".

Correctly setting the delimiter and BOM is the key to successfully parsing CSV:

• Delimiter: Standard CSV uses a comma (,), but some spreadsheet tools (such as the European version of Excel) use a semicolon (;). If the data contains a lot of commas, Tab (\t) is a safer choice. This tool automatically parses the CSV based on the delimiters you choose.
• UTF-8 BOM automatic detection: Some software (such as CSV exported by Excel) will add a BOM tag at the beginning of the file (). After "Automatic BOM Detection" is enabled, the tool will automatically identify and remove the BOM to avoid abnormal characters in the first column name.
• Trim blank: When enabled, the blank characters before and after each field will be automatically cleared to avoid unnecessary spaces causing data comparison errors.

💡 If there are unusual characters at the beginning of the first column name of the CSV, please enable "Automatic BOM Detection".

This tool automatically checks the CSV for common problems and displays the line number and reason:

• The number of fields is inconsistent: If the number of columns in a row does not match the title column (or first row), the tool will pinpoint the specific row number and display the difference between that row and the expected number of columns.
• Empty fields: Check if there is a blank field value and display the position (row and column).
• Repeat Header: If there are duplicate field names in the title column, the duplicate Key will be renamed (e.g. name → name_2) to ensure JSON Key uniqueness.
• Grammar issues: Check whether the quotation mark pairing is complete, whether there are unexpected line breaks, etc.

All errors are displayed in the Errors panel at the top of the tool, with precise line and column numbers so you can fix them quickly.

100% safe. This tool adopts a pure front-end (Client-side) architecture, and all CSV parsing and JSON conversion are completed in your browser.No data will be uploaded to any server。

This means:

• Your customer data, API responses, and trade secrets never leave your computer
• No internet connection is required to perform the conversion (except when loading the page for the first time)
• No backend servers store or process your content
• Even ToolHub administrators cannot access the data you enter

Whether you're working with customer lists, exporting database query results or converting confidential information, it's safe to do it here.