Bazel flag cheat sheet

Navigating Bazel's extensive list of command line flags can be a challenge. This page focuses on the most crucial flags you'll need to know.

Useful general options

The following flags are meant to be set explicitly on the command line.

Flag Description

--config

 You can organize flags in a .bazelrc file into configurations, like ones for debugging or release builds. Additional configuration groups can be selected with --config=<group>.

--keep_going

 Bazel should try as much as possible to continue with build and test execution. By default, Bazel fails eagerly.

--remote_download_outputs

 When using remote execution or caching (both disk and remote), you can signal to Bazel that you want to download all (intermediate) build artifacts as follows: 
--remote_download_outputs=all
By default, Bazel only downloads top-level artifacts, such as the final binary, and intermediate artifacts that are necessary for local actions.

--stamp

 Adds build info (user, timestamp) to binaries.

Uncover Build & Test Issues

The following flags can help you better understand Bazel build or test errors.

Flag Description

--announce_rc

 Shows which flags are implicitly set through user-defined, machine-defined, or project-defined .bazelrc files.

--auto_output_filter

 By default, Bazel tries to prevent log spam and does only print compiler warnings and Starlark debug output for packages and subpackages requested on the command line. To disable all filtering, set --auto_output_filter=none.

--sandbox_debug

 Lets you drill into sandboxing errors. For details on why Bazel sandboxes builds by default and what gets sandboxed, see our sandboxing documentation.

--subcommands (-s)

 Displays a comprehensive list of every command that Bazel runs during a build, regardless of whether it succeeds or fails

Startup

Flag Description

--bazelrc

 You can specify default Bazel options in .bazelrc files. If multiple .bazelrc files exist, you can select which .bazelrc file is used by adding --bazelrc=<path to the .bazelrc file>.

--host_jvm_args

 Limits the amount of RAM the Bazel server uses. For example, the following limits the Bazel heap size to 3GB: 
--host_jvm_args=-Xmx3g

--output_base

 Controls Bazel's output tree. Bazel doesn't store build outputs, including logs, within the source tree itself. Instead, it uses a distinct output tree for this purpose.

Bazel tests

The following flags are related to Bazel test

Flag Description

--java_debug

 Causes Java tests to wait for a debugger connection before being executed.

--runs_per_test

 The number of times to run tests. For example, to run tests N times, add --runs_per_test=N. This can be useful to debug flaky tests and see whether a fix causes a test to pass consistently.

--test_filter

 This flag is particularly useful when iterating on a single test method, such as when a change you made breaks a test. Instead of re-running all the test methods in the test suite, you can focus solely on the specific test(s) that failed. This allows for faster feedback and more efficient debugging. This flag is often used in conjunction with --test_output=streamed for real-time test output.

--test_output

 Specifies the output mode. By default, Bazel captures test output in local log files. When iterating on a broken test, you typically want to use --test_output=streamed to see the test output in real time.

Bazel run

The following flags are related to Bazel run.

Flag Description

--run_under

 Changes how executables are invoked. For example --run_under="strace -c" is commonly used for debugging.

User-specific bazelrc options

The following flags are related to user-specific .bazelrc options.

Flag Description

--disk_cache

 A path to a directory where Bazel can read and write actions and action outputs. If the directory doesn't exist, it will be created. You can share build artifacts between multiple branches or workspaces and speed up Bazel builds by adding --disk_cache=<path> to your command.

--jobs

 The number of concurrent jobs to run. This is typically only required when using remote execution where a remote build cluster executes more jobs than you have cores locally.

--local_resources

 Limits how much CPU or RAM is consumed by locally running actions.

--sandbox_base

 Lets the sandbox create its sandbox directories underneath this path. By default, Bazel executes local actions sandboxed which adds some overhead to the build.

Project-specific bazelrc options

The following flags are related to project-specific .bazelrc options.

Flag Description

--flaky_test_attempts

 Retry each test up to the specified number of times in case of any test failure. This is especially useful on Continuous Integration. Tests that require more than one attempt to pass are marked as FLAKY in the test summary.

--remote_cache

 A URI of a caching endpoint. Setting up remote caching can be a great way to speed up Bazel builds. It can be combined with a local disk cache.

--remote_download_regex

 Force remote build outputs whose path matches this pattern to be downloaded, irrespective of the --remote_download_outputs setting. Multiple patterns may be specified by repeating this flag.

--remote_executor

 HOST or HOST:PORT of a remote execution endpoint. Pass this if you are using a remote execution service. You'll often need to Add --remote_instance_name=<name>.

--remote_instance_name

 The value to pass as instance_name in the remote execution API.

--show-timestamps

 If specified, a timestamp is added to each message generated by Bazel specifying the time at which the message was displayed. This is useful on CI systems to quickly understand what step took how long.

--spawn_strategy

 Even with remote execution, running some build actions locally might be faster. This depends on factors like your build cluster's capacity, network speed, and network delays.