#275 · Developer Tool

CSV Column Type Guesser

Profile CSV columns and infer likely booleans, integers, decimals, dates, JSON values, URLs, emails, or plain text from the observed nonempty cells. Samples nonempty cells in each CSV column and assigns the narrowest type that matches every observed value. Everything runs in the current browser tab, so you can examine the result before copying it into a script, test fixture, migration, or data pipeline.

Developer Input

CSV
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How to use this developer tool

  1. Paste the CSV input or load a local file.
  2. Choose the options that match the source format.
  3. Select Guess Column Types or press Ctrl/Cmd + Enter.
  4. Review the summary and export the output you need.

What this developer tool does

This page samples nonempty cells in each CSV column and assigns the narrowest type that matches every observed value. The main output is ready to copy, while the structured exports retain the diagnostic fields used in the summary.

Integer, decimal, boolean, ISO date, email, URL, and JSON checks run before the text fallback. Empty cells affect nullability but not the guessed type.

Type inference is heuristic. IDs with leading zeroes and locale-specific dates should usually remain text.

Example

Input

id,active,price,created,email
1,true,12.50,2026-07-01,ada@example.com
2,false,8.00,2026-07-02,lin@example.com
3,,9.25,,invalid

Running the sample produces a tool-specific report in the output panel, with counts that correspond to the parsed records or nodes.

Use cases

  • Check incoming CSV before an import or migration.
  • Create repeatable fixtures for parser and ETL tests.
  • Inspect structure without installing a command-line package.
  • Export a compact report for code review or issue tracking.

Tips for reliable output

  • Keep an untouched copy of the source before transforming it.
  • Test one representative edge case as well as the happy path.
  • Review quoted fields, Unicode, and empty values explicitly.
  • Use the JSON export when another program will consume the report.
  • Re-run the tool after changing any parsing option.

Processing details

Integer, decimal, boolean, ISO date, email, URL, and JSON checks run before the text fallback. Empty cells affect nullability but not the guessed type. Processing time is measured in the browser and the original input is left unchanged.

Type inference is heuristic. IDs with leading zeroes and locale-specific dates should usually remain text.

Frequently asked questions

What input does CSV Column Type Guesser accept?

Paste delimited text with a header where the operation requires one. Files are processed locally in the browser.

Does it upload my data?

No. The core processing runs in this page and does not send the pasted content to an API.

How are malformed inputs handled?

The tool stops and shows an error instead of silently returning a partial result.

Can I export the result?

Yes. Copy the main output or download it, and use CSV or JSON export when the structured report is available.

What should I verify before production use?

Type inference is heuristic. IDs with leading zeroes and locale-specific dates should usually remain text.

Output fields

AreaIncluded result
Main outputCopy-ready TXT or text
SummaryCounts and processing note
ExportsCSV and JSON when rows are available

Data & Format Tools

Browse parsers, converters, validators, and format inspection utilities.