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// EFFECT DAYS 2026

This Week in Effect - 143

Effect LSP adds 16 new rules and tsrs --lint support. Effect v4 gains an exact Rational type and OpenRPC document generation. New Effect Days speakers revealed!

Davide Scognamiglio Project Manager Mirela Prifti Community Manager

Hi Effecters! Welcome back to This Week in Effect, your weekly roundup of news from the Effect community and ecosystem.

Recent major announcements:

Technology

  • More news coming to the Effect LSP: 16 new rules and tsrs --lint support!

Effect v4 updates.

New additions in RPC, Schema and persistence alongside the usual round of fixes.

  • Additions: Added an exact Rational numeric type alongside BigDecimal, OpenRPC document generation for RPC groups, and a per-offer deduplicate mode with untilExecuted for PersistedQueue. XML start-element events can now include opt-in source positions, Schema.TaggedUnion and Schema.brand derive their Iso types from the member Iso, and RPC handlers can fail with their middlewareโ€™s errors. Command.validate can now fail with domain errors, and completed cluster requests can be cleaned up by retention.

  • Performance: Large RPC groups are cheaper to type-check in RpcClient and AtomRpc, SchemaBinary encodes large Uint8Array payloads faster, Base64, Base64Url and Hex use the native Uint8Array methods when the runtime provides them, and TestClock is built faster and with less memory.

  • Cluster & workflow: Fixed interrupted defecting cluster requests stalling other entities. Transient persistence failures are now retried for durable clocks, durable deferreds and child workflow starts, and layerMemory replay finalizers are deferred after a defect.

  • AI & MCP: Improved Anthropic support for web fetch and code execution results, including encrypted results, tool search deferral, containers without skills and documents without citations. Fixed OpenAI shell tool results and commentary messages in structured output, streamed shell tool call IDs in stored chats, and empty streamed content deltas in OpenRouter. On the MCP side, requests are now traced with the OpenTelemetry MCP semantic conventions, tool parameters and results go through their JSON codec, and stdio protocols are no longer shared across servers. The Skills extension is restricted to protocol 2026-07-28.

  • HTTP, SQL & platform: Bun servers now close connections after the graceful shutdown timeout, and Bun and Deno servers answer 503 instead of 404 when they have no app. Fixed Bun filesystem writes ignoring the cursor after a seek and child-process interruption hanging on backpressured stdin. Also fixed NodeHttpServer leaving unupgraded upgrade connections open, crashes when collecting encoded Node streams, and HttpClient.withScope now scoping by execution instead of request. PgClient keeps typed SQL errors when the server ends a session in a transaction, MySQL statement cancellation and pool waits are interruptible, and SqlClient driver services stay in the requirements when SqlClient is provided. Migration guidance now covers SQL driver clients no longer extending SqlClient.

  • Core & Schema fixes: The audit continued with Effect race losers now interrupted as soon as the race settles, zero-capacity queues keeping backpressure after batch offers, sliding queues with zero capacity waking waiting takers, RcMap measuring idle time on its makerโ€™s clock, and ScopedCache finalizers no longer retaining requester spans. Also fixed capped fixed-window rate limits, leading U+FEFF in encoded strings, JavaScriptCore Error metadata in Equal and Hash, parser sentinels shared across module copies in Schema, and SchemaBinary accepting non-numbers in f64 runs. Schema.toEquivalence and Schema.toFormatter now derive consistently from the decoded type side, including records with transformed keys, and imported JSON Schema contentSchema annotations that contain references are omitted to avoid dangling references. Also fixed effects hanging when Scheduler.MaxOpsBeforeYield is set to 1 or 2, Request equality depending on field order, and idle OTLP log and trace exporters keeping a timer pending.

You can follow the full changelog in the effect repository.

Other technical updates from the past week.

Effect Core

Effect AI

Effect OpenTelemetry

Community Highlights

  • TanStack AI ๐Ÿค Effect
  • Absolutely insane engineering!
  • ๐Ÿš€

  • Poor Manโ€™s Effect-like DI blog post by Max Khramtsov.

  • live-comments - code comments that cite the ticket or doc behind each business rule. Built on Effect. By BicameralAI.

  • effetch-query - effectful queries and mutations for Effect 4. By monarcode.

  • graft - a hot-swappable plugin framework for Effect. By graftland.

  • strider - browser automation for Effect: scripts, tests and agents that drive Chromium, Firefox or WebKit. By usestrider.

  • return - a minimal file-based router for Effect 4.1 that generates an HttpApi from route.ts files. By chr33s.

  • feeblo - an open-source customer feedback platform with feature request boards, a public roadmap and changelog, an embeddable widget, and a Public API with MCP tools, built on Effect. By G3root.

  • pyfect - Effect for Python: typed errors and dependencies, a fiber runtime with structured concurrency, and layers, checked by pyright. By tylergibbs1.

  • mail-router - a Cloudflare Email Routing Worker that forwards each inbound message to multiple destinations, deployed with Alchemy and built on Effect. By astronautfa.

Effect Job Opportunities

New this week by Aware.

Explore Effect jobs โ†’

Community Events

Visit our Effect Community Events calendar and subscribe for updates on upcoming Effect events.

Effect Team Content Update

  • Effect Office Hours 53 ๐Ÿ”ฅ
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  • Software engineering in the AI era // Cause & Effect 10
Play
  • Community Review: add McpTask for long-running Tools // Office Hours 51
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Cause & Effect Podcast

Donโ€™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.

John A. De Goes, the creator of ZIO, as well as CEO of Ziverge and Golem Cloud, joins Johannes Schickling and Michael Arnaldi to discuss how AI is reshaping software engineering, what developers should still learn, and why Effectโ€™s primitives are especially valuable for coding agents.

Play

Effect Adoption Partner

Weโ€™re thrilled to announce Ziverge as the first Effect Adoption Partner!

New to Effect?

Effect is a TypeScript library for building reliable applications, with built-in concurrency, cancellation, and safe resource management. Explore the documentation and installation guide below to get started.

Effect Community Team

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