The Crystal Programming Language

Crystal talk at FOSDEM 2026

2026-01-23T00:00:00+00:00

I’m giving a talk about Crystal at FOSDEM 2026 in Brussels: Crystal: A language for humans and computers. It’s in the Declarative and Minimalistic Computing track, on Sunday, 1 February 2026 at 09:00 in room UB4.136.

The talk is going to be an introduction into some concepts of Crystals. If you are already familiar with the language, I hope it will still be worthwhile.

If a couple of people are interested in a Crystal meetup, maybe we can arrange to gather somewhere during FOSDEM. Let me know in the comments. I’ll bring some Crystal merch.

Hope to see you in Brussels!

In case you can’t make it, the talk is being recorded.

UPDATE: The talk recording is now available. Thanks to the video team at FOSDEM!

Crystal 1.19.1 is released!

2026-01-20T00:00:00+00:00

We are announcing a new Crystal release 1.19.1 with two regressions fixed.

See the release notes of 1.19.0 for all the changes introduced in Crystal 1.19.

Pre-built packages are available on GitHub Releases and our official distribution channels. See crystal-lang.org/install for installation instructions.

This release includes 2 changes since 1.19.0 by 1 contributor. We thank all the contributors for all the effort put into improving the language! ❤️

This patch release fixes regressions in timer conversions from absolute to relative time (#16581, #16583) that led sleep(seconds) to immediately trigger instead of waiting on some platforms (Darwin, BSDs, Windows) — both introduced in 1.19.0.

For more details, visit the full changelog.

Thanks

We have been able to do all of this thanks to the continued support of 84codes and every other sponsor. To maintain and increase the development pace, donations and sponsorships are essential. OpenCollective is available for that.

Reach out to crystal@manas.tech if you’d like to become a direct sponsor or find other ways to support Crystal. We thank you in advance!

Contribute

Crystal 1.19.0 is released!

2026-01-15T00:00:00+00:00

We are announcing a new Crystal release 1.19.0 with several new features and bug fixes.

Pre-built packages are available on GitHub Releases and our official distribution channels. See crystal-lang.org/install for installation instructions.

This release includes 237 changes since 1.18.2 by 24 contributors. We thank all the contributors for all the effort put into improving the language! ❤️

Below we list the most remarkable changes in the language, compiler and stdlib. For more details, visit the full changelog.

We do not expect any breaking changes in existing code. If you notice any unexpected issues, please let us know in the issue tracker or forum.

The following changes break prior behavior of the compiler, but we expect them to not have much effect in existing code. If you notice any unexpected issues, please let us know in the issue tracker or forum.

The flag? macro is now aware of name-value mappings in the form of name=value where flag?(:name) will now return the respective value as a StringLiteral (#16310). A key without a value returns true as implicit value, as before.

Instead of returning a BoolLiteral the flag? macro might now return a StringLiteral which might be unexpected. The value is still truthy and shouldn’t cause issues in practice.

For example, the value printed by `` may now be:

(not defined) => false
-Dname => true
-Dname=value => "value"
-Dname=some,other,data => "some,other,data"

Thanks, @straight-shoota

The monotonic clock has been adjusted on Linux and macOS to include suspended time, when they previously counted the system uptime.

UNIX targets still use CLOCK_MONOTONIC except for Linux that now uses CLOCK_BOOTTIME (#16516) and macOS that now uses CLOCK_MONOTONIC_RAW instead of mach_absolute_time that internally used CLOCK_UPTIME_RAW (#16516, #16492).

The change is affecting Time.measure for example, that should now include suspended time across the different targets, rather than sometimes including it, and sometimes not.

Execution contexts from RFC 0002 continue as a final preview feature with opt-in with compiler flags -Dpreview_mt -Dexecution_context and we plan to finally enable the feature by default in the 1.20 release!

There has not been huge developments to the feature, but corrections to fix the remaining thread safety issues in the standard library, for example:

Add thread safety to default random (#16174)
Closing system fd is thread unsafe (#16289)
Thread safety of Exception::Callstack (#16504)

We started to merge synchronization primitives from ysbaddaden/sync into the standard library as well:

Add Sync::Mutex and Sync::RWLock (#16399)
Add Sync::ConditionVariable (#16440)
Add Sync::Exclusive and Sync::Shared (#16487)

This effort is part of the ongoing project to improve multi-threading support with the help of 84codes.

Thanks, @ysbaddaden

Introduces the Time::Instant type to represent instants on the monotonic timeline as defined in RFC 0015 instead of overloading the Time::Span type that represents a duration, not an instant (#16490). We expect a clearer and safer API:

Time::Instant represents a single point on the monotonic timeline.
Time::Span continues to represent a duration.
Subtracting two Time::Instant instances yields a Time::Span.
Adding/subtracting a Time::Span to/from an Time::Instant yields a new Time::Instant.

We also adjusted the monotonic clock (#16516), applied the changes (#16498) and deprecated Time.monotonic (#16545).

For example:

timeout = 5.seconds
start = Time.instant

while start.elapsed < timeout
  # do something
end

In order to migrate existing code to Time::Instant, replace calls to Time.monotonic with Time.instant. If the instant time reading is stored in an explicitly typed variable (e.g. an instance variable), change the type from Time::Span to Time::Instant. The APIs of these types are very similar so most use cases should not need any further adaptions.

Finally, we made some further adjustments:

Treat GMT as a legacy alias of UTC (#16292)
Add /etc/zoneinfo to zoneinfo lookup paths (#16463)
Add support for $TZDIR (#16466)

Thanks, @straight-shoota

A long refactor of spawning sub-processes has started. It encompasses a tedious cleanup and safety fixes related to finding the command as well as building the arguments and environment variables, to eventually move on from the classic fork then exec to the more modern posix_spawn on UNIX targets.

Process.run and Process.exec now look up the target executable in the environment of the parent process (ENV["PATH"]) instead of in the environment of the child process (env["PATH"]) on all platforms (#16340). This is usually the expected and specified behaviour for spawning a new process, but it only worked correcly on Windows until now. Consider using a full path (possibly resolved via Process.find_executable) if you want to look up the executable in a different path. With shell: true, the target executable is also looked up in env["PATH"] because the shell process sits in between.

Create argv before fork (#16286, #16321)
Move make_envp before fork (#16351)
Use execvpe when available (#16294, #16311)
Replace Dir.cd with a non-raising alternative in pre-exec (#16352, #16369)
Fix reset directory if Process.exec fails (#16383)
Disable process cancellation during fork (#16446)

Thanks, @straight-shoota

New methods:

Add NamedTuple#reverse_merge (#16229)
Add Set#map! (#16271)
Add Hash#transform_keys! (#16280)
Add OpenSSL::SSL::Context::Server#on_server_name for SNI (#16452, #16525)
Add IPSocket#ipv6_only (#16347)
Add Int.from_digits as inverse of Int#digits (#16237)
Add BigInt.from_digits (#16259)
Add Int#tdivmod (#16258)
Add Random.next_bool and Random.next_int (#16297)
Add Random#split and Random.split for splittable PRNGs (#16342, #16495)
Add Pointer#fill (#16338)
Add Process.debugger_present? for Windows and Linux (#16248)
Add Path#relative? (#16473)
Add YAML::Nodes.parse_all (#16247)
Add ::exit(Process::Status) (#16436)

Enhancements:

Support large JSON files (#16211)
Support deserialization of YAML anchors of value types (#16186)
Add end locations to scalars and aliases in YAML::Nodes.parse (#16187)
Set JSON::SerializableError#attribute when appropriate (#16158)
Add remove_empty parameter to String#each_line (#16232)
Add weeks parameter to Time::Span.new (#16208)
Support 0X, 0O, 0B prefixes in string to integer conversion (#16226)

Thanks, @andrykonchin, @carlhoerberg, @HertzDevil, @ysbaddaden, @straight-shoota, @RX14, @Sija, @spuun

The memory management model for libxml2 changed in Crystal 1.17 to become manual instead of integrating the GC. The change introduced some memory leaks that have now been fixed.

Memory leak in XML.parse and XML.parse_html methods (#16414)
Memory leak in XML::Document#finalize (#16418)
Memory leak in XML::Node#content= (#16419)
Fix use after unlink in XML::Node (#16432)

Thanks, @toddsundsted

New methods:

Thanks, @Blacksmoke16, @HertzDevil

All overloads of ArrayLiteral#[] return nil on out of bounds (#16453)

The Crystal Programming Language

Crystal talk at FOSDEM 2026

Crystal 1.19.1 is released!

Stats

Changes

Crystal 1.19.0 is released!

Stats

Changes

Breaking

Compiler flags now have values

Adjust monotonic clocks

Execution contexts

Time

Process

Standard library

Macros

Compiler

Infra

Dependencies

Deprecations

Crystal 1.18.2 is released!

Stats

Changes

Crystal 1.18.1 is released!

Stats

Changes

Crystal 1.18.0 is released!

Stats

Changes

Execution contexts

Deprecation warnings

Time

Time#inspect

Time::Location

Serialization

Standard library

Networking

Type restrictions

Code Cleanup

Macros

Compiler

Interpreter

Infra

Dependencies

Deprecations

Wind of change (or maybe not)

Crystal 1.17.1 is released!

Stats

Changes

Crystal 1.17.0 is released!

Stats

Changes

Breaking

Colorize only on TTY by default

Manual memory management for libxml2

Blocking behaviour of file descriptors

SystemError.from_errno

Execution Contexts and Multi-Threading

Windows Support

Language

Standard library

Time zone database

Scoped IPv6 addresses

Ensuring string suffix and prefix

Time.month_week_date

Helper methods for subclasses

Compiler

Compiler tools

Infrastructure

Dependencies

Deprecations

Crystal Compass

`Time#inspect`

`Time::Location`

`Colorize` only on TTY by default

Manual memory management for `libxml2`

`SystemError.from_errno`

`Time.month_week_date`