bazel query Command Reference

Inspect the Bazel dependency graph to scope what a change affects.

bazel query answers questions about the target graph: dependencies, reverse dependencies, and which targets a change touches. CI uses it to build and test only what changed.

What it does

bazel query evaluates a query expression against the loaded build graph and prints matching targets. Functions like deps(), rdeps(), and kind() let you find what depends on a changed file, the basis of affected-target CI.

Common flags and usage

'deps(//path:target)': targets a target depends on
'rdeps(//..., //path:lib)': targets that depend on a target
--output=label|package|graph: output format
kind('.*_test', //...): filter by rule kind

Example

shell

# Find and test only what depends on a changed library
TARGETS=$(bazel query 'rdeps(//..., //lib:core)')
bazel test --config=ci ${TARGETS}

In CI

Use rdeps to compute the affected test targets for a PR and run only those, cutting CI time on large monorepos. query reads the graph without building, so it is fast and side-effect free.

Key takeaways

query inspects the target graph without building anything.
rdeps finds reverse dependencies for affected-target CI.
Selective build-and-test from query results cuts monorepo CI time.