Data Format Converter
Convert local CSV, JSON, JSONL and Parquet files, choose column types and preview the result without uploading your data.
Your inputs and files stay in your browser
Source file
Source file
CSV, TSV, JSON array, JSONL or Parquet. One file at a time.
Separator and header settings apply to CSV. Encoding applies to text input. Reopen the file after changing these settings.
File processing stays in this browser. Input, results and SQL are not saved in browser storage or sent to a server.
Input is limited to 1 GiB per file; non-UTF-8 transcoding to 128 MiB. DuckDB has a 512 MiB working-memory budget, not a guarantee that every file fits. JSON/JSONL is decoded as a complete in-memory flat-record set, not in chunks. Text output streams to a supported save picker; Blob fallback is limited to 256 MiB. Parquet output is buffered and capped at 512 MiB. Canceling releases the session.
Columns and result
CSV columns start as text to preserve identifiers and leading zeros. Choose numeric or date types explicitly. Invalid conversions fail instead of becoming null; numeric casts can round values. Keep source types when exact representation matters.
Text output uses UTF-8. JSON is an array of records; JSONL contains one record per line. CSV keeps raw values: formula-like text may execute when opened in spreadsheet software. Parquet output is buffered, not streamed during encoding.
On this page
Convert structured local files between CSV, JSON, JSONL and Parquet without a server upload.
Detailed Functionality
Choose the source format and CSV options, inspect the inferred columns, and select explicit column types where needed. Preview a bounded sample before exporting all records. Conversion runs in a browser worker with DuckDB-WASM loaded only when needed. Text exports use UTF-8; Parquet keeps typed columns. Working memory remains limited by the browser.
Practical Examples
Convert a CSV report to Parquet for analysis. Turn a JSON array into JSONL for line-oriented processing. Export selected Parquet columns to CSV. Preserve identifiers as VARCHAR when leading zeros matter.