Is there a way to limit the number of CPU cores Bazel uses?

some examples for your .bazelrc

build --local_ram_resources=HOST_RAM*.5 --local_cpu_resources=HOST_CPUS-1 (leave one core free)

or

build --local_cpu_resources=1 (use a single core)

See https://docs.bazel.build/versions/master/command-line-reference.html#flag--local_cpu_resources

The currently accepted answer is deprecated.

From Bazel User Manual

--local_resources availableRAM,availableCPU,availableIO

This option, which takes three comma-separated floating point arguments, specifies the amount of local resources that Bazel can take into consideration when scheduling build and test activities. Option expects amount of available RAM (in MB), number of CPU cores (with 1.0 representing single full core) and workstation I/O capability (with 1.0 representing average workstation). By default Bazel will estimate amount of RAM and number of CPU cores directly from system configuration and will assume 1.0 I/O resource.

If this option is used, Bazel will ignore both --ram_utilization_factor.