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Effect Documentation

This Week in Effect - 2026-03-13

Davide Scognamiglio
Davide Scognamiglio
Project Manager
 Mirela Prifti
Mirela Prifti
Community Manager
 Michael Arnaldi
Michael Arnaldi
BDFL

Hi Effecters!

Welcome back to This Week In Effect (TWIE) - your weekly update of the latest developments in the Effect community and ecosystem.

Effect is a powerful TypeScript library that helps developers build complex, synchronous, and asynchronous programs. One key feature that sets Effect apart is how it leverages structured concurrency to provide features such as async cancellation and safe resource management, making it easier to build robust, scalable, and efficient programs.

To get started, below you’ll find links to our documentation as well as our guide for installing Effect. Enjoy!

Recent major updates:

 

Technology

Effect v4 Beta Updates

Here are the most notable changes that landed in effect-smol.

  • AI & toolkit improvements: Added support for toolkit unions in LanguageModel options, fixed toolkit tool requirements inference, fixed fragmented streaming tool calls in openai-compat, and added handling for OpenAI keepalive stream events. HttpClient requests now abort properly after partial stream consumption.

  • CLI & RPC: Added a new effect/unstable/cli/Completions module for shell autocompletion, made Layer.mock a dual API, fixed CLI subcommand context, and ensured RpcGroup.toLayer includes handler dependencies.

  • Schema & Duration: Applied Schema.Json type to toCodecJson and HTTP JSON properties, aligned Schema.toTaggedUnion.match with Data.taggedEnum, fixed Schema.isUUID to make the version parameter optional, and introduced a DurationObject to Duration.Input.

  • Bug fixes & internals: Fixed Cause.hasInterruptsOnly returning false for empty causes, fixed consolePretty ignoring explicit colors in non-TTY environments, made HttpClientResponse pipeable, preserved default logger message item ordering when logging a Cause, fixed Ndjson Uint8Array typing regression, and added a message option to Effect.ignore and Effect.ignoreCause.

You can follow the full changelog directly in the effect-smol repository.

 

Here are all the technical changes from the past week.

Effect AI

 

Community Highlights

  • t3-code is built with Effect 🔥.

 

 

 

  • Effect beats plain TS for agentic coding on multiple fronts, including better token efficiency, as Rhys pointed out.
    Rhys
    Rhys
    @RhysSullivan
    · Follow

    this is why you should be using Effect, in the long term it's much more token efficient than writing standard TS your AI gets knowledge about how your whole system works, what errors can happen, and can leverage the o11y to debug it all

    Image
    Brian Giori
    Brian Giori
    @_bgiori

    What’s the benefit of this over standard TS? Models are already trained on “vanilla” typescript this seems a bit superfluous?

    675
    Reply
    Read 34 replies

 

 

  • effect-htmx – An Effect-first integration for building HTMX-powered applications. Project by Tate Barber.

 

  • effect-atom-jsx – A JSX-based approach to building reactive UIs with Effect atoms. Project by Patrick G.

 

  • Foldkit UI just shipped 14 accessible, unstyled components, making it more practical to build frontend applications where Effect is the foundation. Project by Devin Jameson.

 

Effect Content Update

  • STM in Effect + Community Q&A | Effect Office Hours 20 🔥
Play

 

  • Effect CLI v4 Beta 🚀
Play

 

  • Refactoring with Effect v4 Beta
Play

 

  • Fiber Keep-Alive in Node.js Effect’s Runtime from v3 to v4 | Effect v4 Beta 🚀
Play

 

  • Schedule, Layer, Channel | Effect v4 Beta 🚀
Play

 

  • Filter module, Result module, Layer | Effect v4 Beta 🚀
Play

 

  • Effect Schema v4, Effectful Schemas, Schema Representations
Play

 

Cause & Effect Podcast

Don’t forget to listen to our Cause & Effect podcast hosted by Johannes Schickling and available on YouTube, X(Twitter), and audio platforms like Spotify and Apple Podcast.

Adam Rankin, CTO at Warp, joined Johannes Schickling to talk about using Effect to bring structure and composability to a growing TypeScript codebase, enabling a small, fast-moving team to stay productive while shipping reliable payment & payroll systems.

Play

 

Effect Job Opportunities

More and more companies are adopting Effect in their projects. Here’s a list of companies looking for software engineers with Effect experience:

Disclaimer: Please note that these job postings are shared for informational purposes, and we encourage applicants to verify details directly with the hiring companies.

 

Effect Merch Store

The Effect Merch Store offers a selection of Effect-branded items designed for the community. All orders are processed and fully managed through Printful.

 

Closing Notes

That’s all for this week. Thank you for being a vital part of our community. Your feedback is highly valued as we fine-tune this format. Feel free to share your thoughts, and we’ll do our best to tailor it to the needs of our community.

Effect Community Team

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