About CSV Validator

Validate CSV files with schema checking and error reporting. Part of the DevTools Surf developer suite. Browse more tools in the Data / SQL collection.

Use Cases

• Validate user-uploaded CSV files before database import
• Check exported spreadsheet data for schema conformance before processing
• Verify CSV output from data pipelines meets downstream consumer requirements
• Audit CSV data quality before loading into a BI tool or data warehouse

Tips

• Define a schema with required columns, data types, and constraints before validating — a schema-less validation only catches delimiter and encoding issues
• Use the 'null handling' option to distinguish between empty strings and true null values — many downstream systems treat them differently
• Enable the unique-key validation if your CSV represents a database table — duplicate primary keys are invisible without this check

Fun Facts

• CSV (Comma-Separated Values) has no formal standard — RFC 4180 (2005) documents common usage but acknowledges widespread deviation. This is why CSV parsing fails so often: different tools use different quoting, delimiter, and newline conventions.
• Microsoft Excel's CSV export has a notorious bug: scientific notation is automatically applied to fields that look like numbers (e.g., '1E+10' instead of '1000000000'). This has corrupted gene names in biology research, prompting scientists to rename 20 gene symbols.
• The largest single CSV file known to be regularly used in production belongs to the US Census Bureau's master address file — over 10GB of address data distributed as a single flat file.

FAQ

What are the most common CSV validation failures?

Inconsistent column counts (rows with missing/extra delimiters), unquoted fields containing the delimiter, BOM (byte order mark) at file start causing header parse errors, and mixed line endings (CRLF vs LF). All are detected by this validator.

Should CSV files use commas or semicolons?

RFC 4180 specifies commas. However, European locales that use commas as decimal separators (Germany, France) commonly use semicolons as field delimiters in Excel CSV exports. Always check which convention your data source uses.

How do I handle CSV files with quoted fields containing newlines?

RFC 4180 allows newlines within quoted fields. Most parsers support this, but simple line-by-line processing breaks. Use a proper CSV library (Python's csv module, Papa Parse in JS) rather than splitting on newlines.