EC
CSV::MalformedCSVError
RubyERRORNotableParsing

CSV input is not valid

Quick Answer

Rescue CSV::MalformedCSVError and log the offending line; consider using liberal_parsing: true for lenient mode.

What this means

Raised by the CSV library when input cannot be parsed according to CSV rules — typically due to unclosed quotes, illegal quoting, or characters that violate the configured delimiter/quote settings.

Why it happens
  1. 1Unclosed double-quote in a field
  2. 2Mismatched or illegal use of the quote character
  3. 3File encoding mismatch causing multi-byte sequences to look like stray quotes

Fix

Enable liberal_parsing for tolerant mode

Enable liberal_parsing for tolerant mode
require 'csv'

CSV.parse(data, liberal_parsing: true) do |row|
  process(row)
end

Why this works

liberal_parsing relaxes strict RFC 4180 compliance, accepting many common real-world deviations.

Code examples
Reproducing the errorruby
require 'csv'
CSV.parse('a,"b,c
d,e')
# CSV::MalformedCSVError: Unclosed quoted field on line 1.
Liberal parsingruby
CSV.parse(messy_data, liberal_parsing: true) { |row| puts row }
Rescue per-lineruby
File.foreach('data.csv').with_index(1) do |line, num|
  begin
    CSV.parse_line(line)
  rescue CSV::MalformedCSVError => e
    warn "Line #{num} skipped: #{e.message}"
  end
end
Sources
Official documentation ↗

Ruby Standard Library Documentation

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