CSV ↔ JSON Converter

The 'CSV ↔ JSON Converter' is a completely free, browser-based online data transformation utility essential for data analysts, backend engineers, marketers, and anyone who regularly works with CSV (Comma-Separated Values) files and JSON (JavaScript Object Notation) data.

In modern data workflows, CSV is the standard export format for spreadsheet applications like Excel and Google Sheets, while JSON serves as the de facto global standard for data exchange in Web APIs and NoSQL databases (MongoDB, Firestore). Converting between these two formats is one of the most frequently performed tasks in data migration and analysis pipelines.

In CSV-to-JSON mode, this tool features a high-precision parser that is fully compliant with RFC 4180 (the international standard specification for CSV), correctly handling double-quoted fields containing commas, line breaks, and escaped quotation marks (""). When Excel data contains Japanese addresses like "東京都千代田区丸の内1丁目1番1号" with embedded commas, the tool accurately identifies field boundaries and produces perfect JSON arrays.

In JSON-to-CSV mode, it automatically collects all keys (column names) from every object in the JSON array and fills missing values with empty strings, providing flexible and robust conversion logic. The delimiter is configurable between comma (CSV) and tab (TSV), and JSON indentation width can be adjusted freely between 2-space, 4-space, or minified output. An additional "Parse Numbers" option enables automatic type conversion like "123" → 123 and "true" → true.

Conversion results can be copied to the clipboard with a single click for immediate pasting into Excel or API request bodies. All processing runs entirely within your browser's JavaScript engine, so there is absolutely no need to transmit customer lists, sales data, or personally identifiable information to any server—making it safe for use in even the most compliance-strict enterprise environments.