Required libraries

This is a list of third-party libraries used by the Crystal compiler and the standard library.

Core runtime dependencies

The libraries in this section are always required by Crystal’s stdlib runtime. They must be present for building or running any Crystal program that uses the standard library. Avoiding these dependencies is only possible when not using the standard library (--prelude=none compiler option).

System library

A major component is the system library. Selection depends on the target platform and multiple are supported. This usually includes the C standard library as well as additional system libraries such as libdl, libm, libpthread, libcmt, or libiconv which may be part of the C library or standalone libraries. On most platforms all these libraries are provided by the operating system.

Other runtime libraries

Optional standard library dependencies

These libraries are required by different parts of the standard library, only when explicitly used.

Regular Expression engine

Engine implementation for the Regex class. PCRE2 support was added in Crystal 1.7 and it’s the default since 1.8 (see Regex documentation).

Big Numbers

Implementations for Big types such as BigInt.

Internationalization conversion

This is either a standalone library or may be provided as part of the system library on some platforms. May be disabled with the -Dwithout_iconv compile-time flag. Using a standalone library over the system library implementation can be enforced with the -Duse_libiconv compile-time flag.

TLS

TLS protocol implementation and general-purpose cryptographic routines for the OpenSSL API. May be disabled with the -Dwithout_openssl compile-time flag.

Both OpenSSL and LibreSSL are supported and the bindings automatically detect which library and API version is available on the host system.

Other stdlib libraries

Compiler dependencies

In addition to the core runtime dependencies, these libraries are needed to build the Crystal compiler.