Practice the CSV cases that break simple comparisons.

Explain the result before revealing it. Three real exercises free; no signup, API or input upload. These are original synthetic fixtures.

Download three free exercises · Follow the quoted-newline walkthrough

Ambiguous keys

Left CSV

id,value
C-01,ready
C-01,draft

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Right CSV

id,value
C-01,ready

Download right CSV

Inspect settings

Reveal expected result and explanation

Expected counts: {"unchanged": 0, "changed": 0, "only_left": 0, "only_right": 0, "ambiguous": 1, "blank_key": 0, "invalid_numeric": 0}

Two source records share an ID. No row is selected silently and no business resolution is inferred.

One record can span lines

Left CSV

id,value
C-01,"first
second"

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Right CSV

id,value

C-01,"first
second"

Download right CSV

Inspect settings

Reveal expected result and explanation

Expected counts: {"unchanged": 1, "changed": 0, "only_left": 0, "only_right": 0, "ambiguous": 0, "blank_key": 0, "invalid_numeric": 0}

A quoted newline belongs to one field. Physical line counts do not equal CSV record counts.

Reject incomplete quoted content

Left CSV

id,value
C-01,"unfinished

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Right CSV

id,value
C-01,ready

Download right CSV

Inspect settings

Reveal expected result and explanation

Expected rejection: unclosed quoted

Repair the input using the system of record. Guessing where a quoted field ends could silently change records.

The complete twelve-case lab

Included	Free sample	Full lab
Fixtures, settings, expected answers	3 cases	12 cases
Local viewer and checker	Included	Included
ExportCheck engine	Same original engine	Same original engine

The nine additional cases cover reordered records, blank keys, leading-zero IDs, field mappings, quoted delimiters, decimal tolerance, mixed delimiters, duplicate headers and uneven fields.

Full learning download: $9 USD through Payhip.

What do I need?

A modern browser to read the viewer. Node.js 22+ only for the optional local checker; no paid service.

Is this a general CSV compliance suite?

No. Twelve teaching cases check this engine’s documented rules. They do not prove exhaustive compliance, security or migration correctness. Libraries can intentionally implement different dialects.