Date Column Validator
Pick one CSV column and a date format, then find the exact rows whose dates do not match. Presets for ISO, US, EU, ISO date-time, and RFC 3339, plus custom strftime patterns, delimiter auto-detect, headers or indexes, and JSON output.
About this tool
Date Column Validator checks that every value in one CSV date column parses against a date format you choose, and reports the exact rows that do not. It is useful before importing spreadsheets, partner exports, or analytics feeds into a system that expects a strict date format.
Pick the column by header name (for example joined) or by 0-based index (for example 1 for the second column), choose a format, and run. The report shows how many values were checked, how many are valid, how many are invalid, and — for each offending cell — its data-row number, its line number in the original text, the value, and why it failed.
Formats you can check against
- ISO date —
YYYY-MM-DD, such as2021-06-01(the default). - US date —
MM/DD/YYYY, such as06/15/2021. - EU date —
DD/MM/YYYY, such as15/06/2021. - ISO date-time —
YYYY-MM-DDThh:mm:ss, such as2021-06-01T12:30:00. - RFC 3339 — a full date-time with offset, such as
2021-06-01T12:30:00Z. - Custom pattern — any chrono/strftime pattern in the Custom pattern field, such as
%d-%b-%Yfor01-Jun-2021,%Y%m%dfor20210601, or%H:%M:%Sfor a time of day.
Common specifiers for a custom pattern: %Y four-digit year, %m month, %d day, %b short month name, %H:%M:%S time.
Worked example
Input data:
name,joined
Ada,2021-06-01
Bo,2021/06/02
Cy,2021-13-40
Column joined, format ISO date. The report checks 3 rows, marks 2 valid and 2 invalid: row 2 2021/06/02 uses slashes instead of dashes, and row 3 2021-13-40 is not a real calendar date (month 13, day 40). Impossible calendar dates — month 13, February 30, bad leap days like 2021-02-29 — are rejected, not just badly shaped strings.
CLI example:
gizza tool date-column-validate data="name,joined
Ada,2021-06-01
Bo,2021/06/02" column=joined preset=iso-date has_header=true allow_blank=true delimiter=auto max_issues=50 output=text
Limits and edge cases
The parser handles quoted fields, doubled quotes, delimiters inside quotes, quoted newlines, and blank physical lines. It auto-detects comma, tab, semicolon, and pipe delimiters from the first non-blank line, or you can set the delimiter yourself. Blank cells count as valid by default; turn off Allow blank cells to flag them. The invalid list is capped by Max issues to list (1–1000) so large files stay readable, but the summary always reports the full invalid count. This tool validates one date column at a time and does not fix, reformat, or convert values — it is a report-only checker.
FAQ
How do I validate a CSV that has no header row?
Turn off First row is a header and refer to the column by 0-based index. For example, 0 is the first column and 1 is the second. A numeric value in the Column field is always read as a 0-based index, even when a header is present.
What date formats can I check against?
Presets cover ISO YYYY-MM-DD, US MM/DD/YYYY, EU DD/MM/YYYY, ISO date-time YYYY-MM-DDThh:mm:ss, and full RFC 3339. For anything else, choose Custom pattern and supply a chrono/strftime pattern such as %d-%b-%Y, %Y%m%d, or %H:%M:%S.
Does it catch impossible dates like February 30?
Yes. Values are parsed as real calendar dates, so month 13, day 40, 2021-02-30, and a non-leap 2021-02-29 are all reported as invalid even though they have the right shape.
Are blank cells treated as valid?
By default, yes — blank cells are skipped and counted as valid. Turn off Allow blank cells to report every blank cell in the column as invalid instead.
Why does the report list fewer invalid rows than the invalid count?
The listed rows are capped by Max issues to list (1–1000, default 50) so a large file stays readable. The summary's Invalid count is never capped, so it always reflects the true total; raise the cap to list more offending rows.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool date-column-validate "name,joined
Ada,2021-06-01
Bo,2021/06/02
Cy,2021-13-40" 'column=joined'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/date-column-validate/?data=name%2Cjoined%0AAda%2C2021-06-01%0ABo%2C2021%2F06%2F02%0ACy%2C2021-13-40&column=joined&preset=iso-date&format=%25d-%25b-%25Y&has_header=true&allow_blank=true&delimiter=auto&max_issues=50&output=textMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.