CSV to JSON Converter
Handle Million Rows in Your Browser

Convert CSV files to JSON format instantly in your browser. Handles million-row files with zero upload.

Drag & drop your file here, or browse

Accepts: .csv (up to 500 MB)

Your data stays in your browser. By using this tool, you agree to our Terms and Privacy Policy.

How to Convert CSV to JSON (Large File Support)

Drag and drop your CSV file onto the drop zone at the top of the page, or click to browse and select a file.

Conversion starts automatically and a preview is displayed.

Click the "Download JSON" button to save the converted result.

Key Features of This CSV to JSON Converter

100% Local Processing: Your files are never uploaded to a server. All conversion happens in your browser using WebAssembly, so your sensitive data stays private.
Handles Millions of Rows: Powered by DuckDB-WASM, this tool converts CSV files with over 1 million rows in seconds. Files over 150MB are handled in stable processing mode.
Free with No Limits: No row limits, no file count restrictions, and no account required. Start converting right away.

CSV vs JSON: Differences and Benefits of Converting

CSV (Comma-Separated Values) is a simple tabular format widely compatible with Excel and spreadsheets. JSON (JavaScript Object Notation) represents data as key-value pairs, supporting nested structures and distinct data types.

	CSV	JSON
Structure	Flat table (rows × columns)	Key-value pairs (nestable)
Readability	Easy to view in spreadsheets	Easy to consume in code
Data types	Everything is a string	Strings, numbers, booleans, null
Common use	Data exchange, Excel	Web APIs, config files, NoSQL

Benefits of Converting CSV to JSON

Directly usable in Web APIs and JavaScript applications
Data types (numbers, booleans, null) are preserved, eliminating post-processing
Enables flexible data design with nested structures

Frequently Asked Questions

Is my data uploaded to a server?

No. Your file never leaves your browser. All processing happens locally using WebAssembly. No data is sent to any server.

Is it free?

Yes, this tool is completely free with no row limits.

Can I convert a large CSV file with millions of rows to JSON?

Yes. This tool uses DuckDB-WASM to process files entirely in your browser. It can handle millions of rows without crashing or uploading your data, and supports large files depending on your device's available memory. Files over 150MB automatically switch to "stable processing mode," which writes the output directly to disk to avoid browser memory pressure.

Does the tool handle different text encodings (prevent garbled text)?

Yes. Our tool automatically detects and converts most global text encodings on the fly. We fully support UTF-8, UTF-16, Windows-1252, ISO-8859-1 (Latin-1), and various other international formats, ensuring your data is parsed perfectly without broken characters.

What JSON format is the output?

The output is an array of objects, where each object represents a row and keys are the column headers from your CSV.

How large will the JSON file be after converting from CSV?

JSON includes column names for every row, so the output is larger than CSV. Here are rough estimates:

CSV	JSON (estimate)
10MB	30–50MB
50MB	150–250MB
100MB	300–500MB
200MB	600MB–1GB
300MB	900MB–1.5GB
500MB	1.5–2.5GB

* Actual size varies depending on the number of columns and data content.

What is the file size limit for CSV to JSON conversion?

The limit is 500MB for CSV to JSON conversion. Since JSON output includes column names for every row, the output file can be 2-3x larger than the input CSV, so we limit input size to prevent browser memory issues.

Can I remove columns or filter data before converting?

This page is a dedicated conversion tool. If you need to remove unnecessary columns, filter data by conditions, or merge multiple files before converting, try the data analysis platform LeapRows. No account required — start using it right in your browser.

Can I use this on a smartphone or tablet?

Yes, it works on any device with a modern browser. However, for large file processing and easier file management after download, we strongly recommend using a desktop or laptop computer.

What browsers are supported?

Any modern browser that supports WebAssembly: Chrome, Firefox, Edge, Safari (14+). Chrome is recommended for best performance with large files.