sniff.md

sniff

Quickly sniff & infer CSV metadata (delimiter, header row, preamble rows, quote character, flexible, is_utf8, average record length, number of records, content length & estimated number of records if sniffing a CSV on a URL, number of fields, field names & data types). It is also a general mime type detector.

Table of Contents | Source: src/cmd/sniff.rs | 📇🌐🤖

Description | Examples | Usage | Arguments | Sniff Options | Common Options

Description ↩

Quickly sniff the first n rows and infer CSV metadata (delimiter, header row, number of preamble rows, quote character, flexible, is_utf8, average record length, number of records, content length and estimated number of records if sniffing a URL, file size, number of fields, field names & data types).

sniff is also a mime type detector, returning the detected mime type, file size and last modified date. If --no-infer is enabled, it doesn't even bother to infer the CSV's schema. This makes it useful for accelerated CKAN harvesting and for checking stale/broken resource URLs.

When qsv is compiled with the optional magika feature, it uses Magika - Google's AI-powered content detection library to identify file types with high accuracy. Magika detects over 200 content types including CSV, parquet, MS Office/Open Document files, JSON, PDF, PNG, JPEG & more. See https://opensource.googleblog.com/2025/11/announcing-magika-10-now-faster-smarter.html.

When the magika feature is not enabled in a build (e.g., MUSL builds, qsvlite, qsvdp), it falls back to the file-format library which provides basic MIME type detection.

NOTE: This command "sniffs" a CSV's schema by sampling the first n rows (default: 1000) of a file. Its inferences are sometimes wrong if the the file is too small to infer a pattern or if the CSV has unusual formatting - with atypical delimiters, quotes, etc.

In such cases, selectively use the --sample, --delimiter and --quote options to improve the accuracy of the sniffed schema.

If you want more robust, guaranteed schemata, use the "schema" or "stats" commands instead as they scan the entire file. However, they only work on local files and well-formed CSVs, unlike sniff which can work with remote files, various CSV dialects and is very fast regardless of file size.

Examples ↩

Sniff a local CSV file

qsv sniff data.csv

Sniff a remote TSV file over HTTPS

qsv sniff https://example.com/data.tsv

Get the mime type of a remote file without inferring the CSV schema

qsv sniff --no-infer https://example.com/data.xlsx

Sniff the first 20 percent of a SSV file

qsv sniff --sample 0.20 data.ssv

For more examples, see tests.

Usage ↩

qsv sniff [options] [<input>]
qsv sniff --help

Arguments ↩

Argument	Description
<input>	The file to sniff. This can be a local file, stdin or a URL (http and https schemes supported).

Sniff Options ↩

Option	Type	Description	Default
‑‑sample	string	First n rows to sample to sniff out the metadata. When sample size is between 0 and 1 exclusive, it is treated as a percentage of the CSV to sample (e.g. 0.20 is 20 percent). When it is zero, the entire file will be sampled. When the input is a URL, the sample size dictates how many lines to sample without having to download the entire file. Ignored when --no-infer is enabled.	1000
‑‑prefer‑dmy	flag	Prefer to parse dates in dmy format. Otherwise, use mdy format. Ignored when --no-infer is enabled.
‑d, ‑‑delimiter	string	The delimiter for reading CSV data. Specify this when the delimiter is known beforehand, as the delimiter inferencing algorithm can sometimes fail. Must be a single ascii character.
‑‑quote	string	The quote character for reading CSV data. Specify this when the quote character is known beforehand, as the quote char inferencing algorithm can sometimes fail. Must be a single ascii character - typically, double quote ("), single quote ('), or backtick (`).
‑‑json	flag	Return results in JSON format.
‑‑pretty‑json	flag	Return results in pretty JSON format.
‑‑save‑urlsample	string	Save the URL sample to a file. Valid only when input is a URL.
‑‑timeout	string	Timeout when sniffing URLs in seconds. If 0, no timeout is used.	30
‑‑user‑agent	string	Specify custom user agent to use when sniffing a CSV on a URL. It supports the following variables - $QSV_VERSION, $QSV_TARGET, $QSV_BIN_NAME, $QSV_KIND and $QSV_COMMAND. Try to follow the syntax here - https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent
‑‑stats‑types	flag	Use the same data type names as stats. (Unsigned, Signed => Integer, Text => String, everything else the same)
‑‑no‑infer	flag	Do not infer the schema. Only return the file's mime type, size and last modified date. Use this to use sniff as a general mime type detector. Note that CSV and TSV files will only be detected as mime type plain/text in this mode.
‑‑just‑mime	flag	Only return the file's mime type. Use this to use sniff as a general mime type detector. Synonym for --no-infer.
‑Q, ‑‑quick	flag	When sniffing a non-CSV remote file, only download the first chunk of the file before attempting to detect the mime type. This is faster but less accurate as some mime types cannot be detected with just the first downloaded chunk.
‑‑harvest‑mode	flag	This is a convenience flag when using sniff in CKAN harvesters. It is equivalent to --quick --timeout 10 --stats-types --json and --user-agent "CKAN-harvest/$QSV_VERSION ($QSV_TARGET; $QSV_BIN_NAME)"

Common Options ↩

Option	Type	Description	Default
‑h, ‑‑help	flag	Display this message
‑p, ‑‑progressbar	flag	Show progress bars. Only valid for URL input.

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Source: src/cmd/sniff.rs | Table of Contents | README