CRYSTAL-BUILD(1) Crystal Compiler Command Line Reference Guide CRYSTAL-BUILD(1)

crystal-build - Compile a Crystal program

crystal build [options] [programfile] [--] [arguments]

--cross-compile

Generate an object file for cross compilation and prints the command to build the executable. The object file should be copied to the target system and the printed command should be executed there. This flag mainly exists for porting the compiler to new platforms, where possible run the compiler on the target platform directly.

-d, --debug

Generate the output with symbolic debug symbols. These are read when debugging the built program with tools like lldb, gdb, valgrind etc. and provide mappings to the original source code for those tools.

--no-debug

Generate the output without any symbolic debug symbols.

-D FLAG, --define FLAG

Define a compile-time flag. This is useful to conditionally define types, methods, or commands based on flags available at compile time. The default flags are from the target triple given with --target-triple or the hosts default, if none is given.

--emit [asm|llvm-bc|llvm-ir|obj]

Comma separated list of types of output for the compiler to emit. You can use this to see the generated LLVM IR, LLVM bitcode, assembly, and object files.

--x86-asm-syntax [att|intel]

Select the assembly dialect for --emit=asm. The default is att, which stands for the AT&T syntax supported by tools like the GNU Assembler. intel selects the Intel syntax which is preferred for Windows tools.

--frame-pointers [auto|always|non-leaf]

Control the preservation of frame pointers. The default value, --frame-pointers=auto, will preserve frame pointers on debug builds and try to omit them on release builds (certain platforms require them to stay enabled). --frame-pointers=always will always preserve them, and non-leaf will only force their preservation on non-leaf functions.

-f text|json, --format text|json

Format of output. Defaults to text. The json format can be used to get a more parser-friendly output.

--error-trace

Show full error trace. Disabled by default, as the full trace usually makes error messages less readable and may not always deliver relevant information.

--ll

Dump LLVM assembly file to output directory.

--link-flags FLAGS

Pass additional flags to the linker. Though you can specify those flags on the source code, this is useful for passing environment specific information directly to the linker, like non-standard library paths or names. For more information on specifying linker flags on source, you can read the "C bindings" section of the documentation available on the official web site.

--mcpu CPU

Specify a specific CPU to generate code for. This will pass a -mcpu flag to LLVM, and is only intended to be used for cross- compilation. For a list of available CPUs, pass --mcpu help when building any Crystal source code. Passing --mcpu native will pass the host CPU name to tune performance for the host.

--mattr CPU

Override or control specific attributes of the target, such as whether SIMD operations are enabled or not. The default set of attributes is set by the current CPU. This will pass a -mattr flag to LLVM, and is only intended to be used for cross-compilation. For a list of available attributes, invoke llvm-as < /dev/null | llc -march=xyz -mattr=help.`

--mcmodel default|kernel|tiny|small|medium|large

Specifies a specific code model to generate code for. This will pass a --code-model flag to LLVM.

--no-color

Disable colored output.

--no-codegen

Don’t do code generation, just parse the file.

-o FILE, --output FILE

Specify output path. If a directory, the filename is derived from the first source file (default: current directory)

--prelude

Specify prelude to use. The default one initializes the garbage collector. You can also use --prelude=empty to use no preludes. This can be useful for checking code generation for a specific source code file.

-O LEVEL

Optimization mode: 0 (default), 1, 2, 3. See OPTIMIZATIONS for details.

--release

Compile in release mode. Equivalent to -O3 --single-module

-s, --stats

Print statistics about the different compiler stages for the current build. Output time and used memory for each compiler process.

-p, --progress

Print statistics about the progress for the current build.

-t, --time

Print statistics about the execution time.

--single-module

Generate a single LLVM module. By default, one LLVM module is created for each type in a program. --release implies this option.

--threads NUM

Maximum number of threads to use for code generation. The default is 8 threads.

--target TRIPLE

Enable target triple; intended to use for cross-compilation. See llvm documentation for more information about target triple.

--verbose

Display the commands executed by the system.

--static

Create a statically linked executable.

--stdin-filename FILENAME

Source file name to be read from STDIN.
2026-07-23 crystal 1.21.0