`sniff`

Reports file properties: detected or assumed encoding, field types, record count, and the CSV delimiter currently in use.

sniff does not auto-detect the CSV delimiter. The CLI default is --delimiter ,. A semicolon-separated file is reported as a single column unless you pass --delimiter ";". Use analyze when you need delimiter auto-detection.

Encoding is often unknown when sniff cannot determine it; pass --encoding to override.

# Report file properties (text output)
undatum sniff data.csv

# Semicolon CSV: pass the delimiter
undatum sniff data.csv --delimiter ";"

# Output as JSON (also --format-out json, or --output ending in .json)
undatum sniff data.jsonl --format-out json

# Output as YAML
undatum sniff data.csv --format-out yaml --output sniff.yaml
undatum sniff nested.jsonl --flatten-nested --format-out json

Reference

Reads: any readable format · Writes: report (see --format-out) · Memory: bounded: the beginning of the file · Engines: python

undatum sniff [OPTIONS] INPUT_FILE

Argument	Description
`INPUT_FILE`	Path to input file. (required)

Option	Description	Default
`-o`, `--output` TEXT	Optional output file path. If not specified, prints to stdout.
`-O`, `--format-out` TEXT	Output format: 'text' (default), 'json', or 'yaml'. Also inferred when --output ends in .json/.yaml/.yml.
`-d`, `--delimiter` TEXT	CSV delimiter character (auto-detected when omitted).
`--quotechar` TEXT	CSV quote character (iterabledata default '"' when omitted).
`--encoding` TEXT	File encoding (e.g., 'utf8', 'latin1').
`--verbose` / `--no-verbose`	Enable verbose logging output.	`--no-verbose`
`-F`, `--format-in` TEXT	Override input file format detection (e.g., 'csv', 'jsonl').
`--table`, `--sheet` TEXT	Table or sheet name for multi-table sources (Excel, SQLite, lakehouse).
`--start-page` INTEGER	Sheet index (0-based) for Excel files.	`0`
`--trust`	Acknowledge pickle deserialization risk when reading pickle sources.
`--on-error` TEXT	Parse-error policy: raise (default), skip, or warn.
`--error-log` TEXT	Append parse errors as JSONL (use with --on-error skip or warn).
`--flatten-nested`	Unfold nested dict / array-of-dict fields into dotted paths (e.g. city.lat).
`--max-nested-depth` INTEGER	With --flatten-nested, maximum nest depth to unfold (engine default 5).
`--keep-nested-parents` / `--no-keep-nested-parents`	With --flatten-nested, keep parent dict/array fields alongside dotted children.	`--keep-nested-parents`
`--json`	Print the result as one JSON document (same as --format-out json).

Deprecated spellings (removed in 2.0): --format → --format-out.

Reference​

Reference