Convert CSV to Parquet
Convert CSV files to Parquet with ZSTD compression, locally in your browser. No upload, no signup — typed columns are inferred automatically.
Why convert CSV to Parquet?
CSV is universal but expensive: every read parses text, types are guessed by every consumer independently, and the file compresses poorly. Parquet fixes all three — typed columns, columnar layout and built-in compression — which is why data warehouses, lakehouses, pandas, Polars and DuckDB all read it natively. Converting once and querying many times is almost always worth it.
How this converter works
- Drop a
.csvfile above. - DuckDB's CSV sniffer detects the delimiter, header and column types from a sample of the file.
- The data is written as Parquet with ZSTD compression and downloads automatically.
Everything happens inside your browser — the file is never uploaded, which makes this safe for customer exports, financial data and anything else you would not paste into a cloud tool.
Checking the result
Want to confirm the schema came out right? Open the downloaded file in the Parquet Viewer to see the inferred column types, row count and compression, or run a quick aggregation in the SQL Workbench before shipping the file into your pipeline.
Frequently asked questions
- How are column types decided?
- DuckDB samples the CSV and infers types automatically — integers, floats, dates, timestamps and booleans are detected. Anything ambiguous falls back to text.
- What compression does the output use?
- The output is written with Zstandard (ZSTD) compression, which typically shrinks a CSV to a fraction of its original size while staying fast to read in every modern Parquet reader.
- My CSV uses semicolons or tabs — will it work?
- Yes. The delimiter, quoting style and header row are auto-detected by DuckDB's CSV sniffer, which handles the vast majority of real-world CSV dialects.
- Why is my Parquet file so much smaller than the CSV?
- Parquet stores each column together and compresses it, so repeated values and predictable patterns compress extremely well. A 5-10x size reduction is common.