where - the free filter

Keep rows matching a deterministic predicate. Free - where never calls a model. Streams, preserves input order, and emits matching rows byte-for-byte.

tail -f app.log \
| smartpipe where 'text has "ERROR"'
cat orders.jsonl \
| smartpipe where 'total > 1000'

Rule of thumb: where for facts, filter for judgment - the filter-early habit is Learn chapter 4.

The predicate language

Form	Meaning
FIELD has "word"	word-bounded match, case-insensitive
FIELD contains "text"	substring, case-insensitive
FIELD matches /re/	Python regex search, case-sensitive
FIELD == VALUE / !=	numeric when both sides are numbers, temporal when both are ISO dates/datetimes, else exact string
FIELD > >= < <=	numeric, or temporal when both sides are ISO dates/datetimes - anything else never matches (and is disclosed)
and · or · not · ( )	not binds tightest, then and, then or

FIELD is a record field name, or text for the whole line (on plain-text input, text is the only field there is). It can also be a field path into nested records - where 'user.plan has "pro" and items[0].total >= 100' - where a literal flat column named user.plan wins first and a path miss counts as an ordinary missing field. Booleans compare by their JSON spelling: pass == true. Temporal comparison (due >= "2026-01-01") kicks in when both sides read as ISO dates/datetimes - a bare date counts as its midnight, so a {due date} field extracted upstream compares as time, not text.

Missing fields

Missing fields evaluate false - streams keep flowing - but the run ends with a disclosure noting which fields were missing:

where: 2,114 of 104,882 matched
note: field 'level' missing on 12,004 rows

Zero matches exits 0 (an empty result is a valid result, like filter). A predicate the grammar can't parse exits 64 with the full operator menu, before any input is read.