External dependencies

CRuby has very few hard dependencies on external software at build time. The list grows considerably if you enable the optional C extensions in ext/.

Core build (no extensions)

Dependency	Purpose	Required?
C compiler (C99 or newer)	Compile the interpreter	Required
make (GNU make works; BSD make also OK)	Drive the build	Required
autoconf	Regenerate configure from configure.ac (only when editing configure.ac)	Recommended for development
Ruby (any recent version)	Bootstrap; runs Lrama and Ruby-implemented build helpers	Required (BASERUBY)
dlopen/dlsym (or Windows equivalent)	Load C extensions at runtime	Required for shared-extension builds
POSIX threads (pthread)	Backing native threads	Required on POSIX
libm	math functions	Required

That's it for a minimal ./configure --without-ext --disable-yjit --disable-zjit --disable-install-doc build. No GMP, no zlib, no OpenSSL — everything else is optional.

Optional core dependencies

Dependency	Used by	Effect of absence
libffi	Fiddle, Etc callbacks (limited)	Some functionality unavailable
Clang / GCC builtins	YJIT/ZJIT bindgen	Slower or missing JIT
Rust (≥ 1.85.0)	YJIT, ZJIT	JITs not built (with --enable-yjit requires Rust)

For a JIT-enabled build:

Rust ≥ 1.85.0          # see Cargo.toml's rust-version
cargo (bundled with Rust)

The Rust dependency is only required if you build with --enable-yjit or --enable-zjit.

C extension dependencies

Each extension in ext/ may need OS headers and libraries. The build skips extensions whose dependencies aren't present (with a warning) and continues. The most commonly-required external libraries:

Extension	External library	Notes
ext/openssl	OpenSSL ≥ 1.0.2 (or LibreSSL ≥ 3.x)	TLS, hashing, crypto
ext/psych	libyaml ≥ 0.1.7	YAML 1.1
ext/zlib	zlib	Compression
ext/digest/*	OpenSSL (optional)	Falls back to built-in implementations if absent
ext/socket	libnsl, libsocket (Solaris); built-in elsewhere	Sockets
ext/readline (where built)	GNU readline OR libedit	Interactive line editing
ext/gdbm (where built)	gdbm	DBM database
ext/dbm (where built)	various dbm	DBM database
ext/syslog (where built)	libsyslog (most platforms have it built-in)	syslog(3)
ext/etc	(none — uses libc)	Unix /etc/passwd
ext/pty	various tty libraries (most built-in)	PTY allocation
ext/json	(none — pure C)	JSON

tool/extlibs.rb can fetch and build several of these from source for offline / hermetic builds. The list of bundled builders is in tool/extlibs.rb (e.g., openssl, gmp, libffi, libyaml).

RDoc / documentation

Dependency	Purpose	Required?
rdoc	Generate API docs	Built-in (vendored under lib/rdoc/)
groff	Render manpages	Optional (only make install uses it)

--disable-install-doc skips RDoc generation entirely; this is the fastest install option.

Test dependencies

Dependency	Purpose	Notes
test-unit	make test-all runner	Vendored at tool/lib/test/unit.rb
mspec	make test-spec runner	Vendored at spec/mspec/
bundler	make test-bundled-gems	Vendored as default gem

All test dependencies are vendored — no network access required.

Bundled gems (installed alongside Ruby)

Bundled gems are not sources — they're fetched as gems at install time. The list pinned for the current build is in gems/bundled_gems:

minitest 6.0.5
power_assert 2.x
rake 13.4.2
test-unit 3.7.7
rexml 3.x
rss 0.x
matrix 0.x
prime 0.x
bigdecimal 3.x
mutex_m 0.x
csv 3.x
fiddle 1.x
logger 1.x
ostruct 0.x
pstore 0.x
benchmark 0.x
getoptlong 0.x
debug 1.x
racc 1.x
tsort 0.2.0
win32-registry 0.1.2

These are downloaded from rubygems.org (or a configured mirror) at install time. They're not required for the build itself.

Default gems (shipped vendored in lib/ and ext/)

Every default gem is vendored — its source is in this repo and synced from upstream by tool/sync_default_gems.rb. A non-exhaustive list with their upstream:

Gem	Upstream
prism	github.com/ruby/prism
optparse	github.com/ruby/optparse
uri	github.com/ruby/uri
psych	github.com/ruby/psych
json	github.com/ruby/json
irb	github.com/ruby/irb
reline	github.com/ruby/reline
rdoc	github.com/ruby/rdoc
rubygems / bundler	github.com/rubygems/rubygems
did_you_mean	github.com/ruby/did_you_mean
error_highlight	github.com/ruby/error_highlight
syntax_suggest	github.com/ruby/syntax_suggest
forwardable	github.com/ruby/forwardable
delegate	github.com/ruby/delegate
pathname	github.com/ruby/pathname
fileutils	github.com/ruby/fileutils
tempfile	github.com/ruby/tempfile
tmpdir	github.com/ruby/tmpdir
time	github.com/ruby/time
timeout	github.com/ruby/timeout
prettyprint	github.com/ruby/prettyprint
pp	github.com/ruby/pp
set	github.com/ruby/set
singleton	github.com/ruby/singleton
monitor	github.com/ruby/monitor
weakref	github.com/ruby/weakref
ipaddr	github.com/ruby/ipaddr
resolv	github.com/ruby/resolv
securerandom	github.com/ruby/securerandom
cgi	github.com/ruby/cgi
erb	github.com/ruby/erb
net-protocol, net-http, net-smtp, net-imap	github.com/ruby/net-*
openssl	github.com/ruby/openssl
digest	github.com/ruby/digest
socket	github.com/ruby/socket
etc, fcntl, pty, zlib, stringio, strscan, date	github.com/ruby/

The full mapping is in tool/sync_default_gems.rb's REPOSITORIES hash.

Cargo dependencies (YJIT / ZJIT)

Cargo.toml at the repo root declares no required runtime dependencies:

[dependencies]
yjit = { path = "yjit", optional = true }
zjit = { path = "zjit", optional = true }

yjit/Cargo.toml and zjit/Cargo.toml declare optional dev-time dependencies (capstone for disassembly, bindgen for FFI codegen). Release builds use rustc directly without Cargo, sidestepping these.

Vendored licenses

Third-party code shipped in the tree:

• Onigmo (reg*.c) — BSD-style. Original Oniguruma copyright by K. Kosako; Onigmo additions by various.
• st.c — Originally a public-domain hash table by Peter Moore; heavily modified.
• siphash.c — by Jean-Philippe Aumasson and Daniel J. Bernstein. CC0.
• vsnprintf.c — BSD-licensed snprintf implementation.
• CCAN (ccan/) — small utility code from the Comprehensive C Archive Network. Various BSD-style licenses.
• prism — MIT (Shopify).
• YJIT/ZJIT — Same license as Ruby itself.
• MMTk binding — MIT (the binding); MMTk itself is MIT.

The full inventory is in LEGAL (~56 KB). The top-level COPYING file is the standard Ruby license (a dual BSDL / Ruby's own license).