RFC 4180 defines a CSV file as records separated by line breaks, with fields separated by commas. A field that contains a comma, a double quote or a line break is enclosed in double quotes, and a literal quote is doubled.
01The rules that matter
The delimiter is a single character; CSV uses a comma, TSV a tab and PSV a pipe.
A quoted field may contain the delimiter, a newline or a doubled quote.
Records end with CRLF, LF or CR; a UTF-8 BOM may precede the first field.
Cells are text: CSV has no types, so numbers and booleans are strings.
02Detecting a dialect
When the dialect is unknown, score each candidate delimiter by how consistently the column count holds across the sampled records and choose the most consistent one.
Frequently asked questions
Why are my numbers strings?
A CSV cell is text by definition; any typing is an inference applied afterwards.
What ends a record?
CRLF, LF or CR. The parser tolerates all three and reports mixed endings.
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