RFC 4180 CSV Validation: The Complete Guide

What is RFC 4180?

RFC 4180 (also written RFC4180) is a memo published by the Internet Engineering Task Force (IETF) that defines the common format and MIME type for Comma-Separated Values (CSV) files. While not a formal standard, RFC 4180 is the de facto specification that most CSV parsers and validators use as their reference.

RFC 4180 compliance means your CSV file follows the rules defined in this specification—making it reliably parseable by any compliant CSV parser, regardless of platform or programming language.

Key RFC 4180 Rules

Comma Delimiter Only

RFC 4180 specifies the comma (,) as the field delimiter. Tab-separated (TSV), semicolon-separated, and pipe-separated files are not RFC 4180 compliant CSV files—they are different formats entirely.

Double-Quote Field Enclosure

Fields containing commas, line breaks, or double-quote characters must be enclosed in double quotes ("). Single quotes are not valid field enclosures under RFC 4180.

Double-Quote Escaping (No Backslash)

A double-quote character within a quoted field must be escaped by doubling it: "". Backslash escaping (\") is invalid under RFC 4180 and will cause parsing failures in compliant parsers.

Consistent Column Counts

Every record (row) in an RFC 4180 compliant file must contain the same number of fields. Rows with more or fewer fields than the header row are a compliance violation.

CRLF or LF Line Endings

RFC 4180 specifies CRLF (\r\n) as the line terminator, but LF (\n) is also widely accepted. CR-only (\r) line endings are not supported and will cause the file to be treated as a single line.

Optional Header Row

RFC 4180 allows an optional header row as the first record. When present, the header row must contain the same number of fields as all other records. CSV Workbench requires a header row and validates that column names are unique and non-empty.

Common RFC 4180 Violations

Violation	Example
Backslash quote escaping	\"value\"
Unquoted field with comma	1,000,000
Inconsistent column count	Row 5 has 3 fields, header has 4
CR-only line endings	File treated as single line
Non-UTF-8 encoding	Latin-1 or Windows-1252 characters
Unmatched quote character	"unclosed field

How CSV Workbench Validates RFC 4180 Compliance

CSV Workbench enforces strict RFC 4180 (RFC4180) compliance automatically when you add a CSV file. The WebAssembly-powered validation engine checks:

UTF-8 encoding validation
Comma delimiter enforcement (no tabs, semicolons, or pipes)
Double-quote field enclosure and escaping rules
Consistent column counts across all rows
CRLF or LF line ending compliance (CR-only rejected)
Header row presence, uniqueness, and non-empty column names
CSV injection protection (fields starting with =, +, -, @, |)

If any RFC 4180 violation is detected, CSV Workbench provides a detailed error report with the exact row and column location of each issue, along with actionable suggestions for fixing the problem. Files that fail RFC 4180 validation cannot be saved as references until the issues are resolved.

RFC 4180 Validation vs. CSV Schema Validation

RFC 4180 validation checks the structure of a CSV file—is it a valid CSV? CSV Schema validation goes further, checking the content—do the values match the expected data types and constraints?

RFC 4180 validation: Is this a well-formed CSV file? (structure, encoding, delimiters, quoting)
CSV Schema validation: Does this CSV file contain the right data? (types, ranges, patterns, required fields)

CSV Workbench performs both automatically. RFC 4180 validation runs first when you add a file; CSV Schema validation runs when you click Validate Data with an associated schema.