This Week in Effect - 141

Effect shipped its 141st weekly ecosystem update, adding a native McpClient, an effect/persistence/CircuitBreaker module, Schema.toStandardJSONSchemaV1, a TextDiff module for minimal edit scripts and unified diffs, and Cloudflare AI Gateway support to the TypeScript library. The release also encrypts EventLog entries in batches with hybrid logical clock ids and adds EventLog.writeMany, opt-in request batching to the HTTP RPC client protocol, HTTP/2 servers in NodeHttpServer, and OpenAI safety_identifier and prompt_cache_retention request options. The changes matter to developers building concurrent and AI-backed TypeScript services because they add MCP client support, idempotent cluster handling, and new streaming encodings including zip, XML and JsonArray.

Hi Effecters Welcome back to This Week in Effect, your weekly update of the latest developments in the Effect community and ecosystem. Effect is the TypeScript library for the AI era, helping 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 and our guide for installing Effect. Enjoy Recent major updates: New Module of the Week https://effect.website/blog/module-of-the-week/cluster-idempotency post by Maxwell Brown https://x.com/maxwellbrown , delving into Cluster idempotency . At-least-once delivery means you never lose a message, but you'll sometimes get the same one twice. This week learn how to: → Make handlers idempotent → Skip duplicate messages → Deal with the dual write problem Module of the Week: Cluster, Part 4 ↓ A week of new modules and a big push on EventLog , alongside the ongoing stream of fixes across the codebase. Here are the most notable changes. - Additions : Added a native McpClient , effect/persistence/CircuitBreaker , Schema.toStandardJSONSchemaV1 , a TextDiff module for minimal edit scripts and unified diffs, and Cloudflare AI Gateway support. Streaming encodings now include zip, XML and JsonArray for large JSON arrays, and Base64Url.encodePadded was added. Also added typed HTTP date and Retry-After header values to Headers , FileSystem.lstat , Flag.withNegation and Flag.withoutNegation , Command.validate for rules across CLI flags, a skipInitialRun option for seeded effect atoms, and deterministic concurrent property checking for tests. - EventLog : Entries are now encrypted in batches and get ids from a hybrid logical clock, with EventLog.writeMany and monotonic entry ids. Conflicts are ordered by entry id across journals and server, writes are acknowledged rather than echoed to the writer, and compaction can now drop entries only. SqlEventJournal gained upload checkpoints and secondary indexes, and remote replay was sped up with cached conflict payloads, indexed lookups and less per-entry overhead. Also fixed out-of-order unencrypted replication, duplicate encrypted SQL event broadcasts, and several IndexedDB journal and checkpoint issues. - Cluster & workflow : Fixed shard release stalling on a defect restart, ClusterCron initial scheduling recovery, duplicate workflow compensations after memory-engine replays, and interrupts being lost while a workflow run saves its Suspended reply. Stalled shard releases are now warned about repeatedly, with a new releasing-shards gauge and a shard release duration timer. Cluster storage reads also wake up when an entity registers. - HTTP, RPC & platform : Added opt-in request batching to the HTTP RPC client protocol, streaming request payload support to HttpApi , and HTTP/2 servers in NodeHttpServer . Forwarded headers now require a trusted proxy policy. Fixed HttpClient.followRedirects dying on an invalid Location header, basicAuth credentials not being encoded as UTF-8, multipart Content-Disposition filename decoding, and NodeHttpServer ending failed streamed responses as complete. On the runtime side, fixed Bun WebSocket interruption on close, Deno response failures and Socket.readerString corrupting characters split across frames. - SQL & AI : PgClient gained an onAcquire hook and an acquireTimeout , PostgreSQL server errors are preserved when the connection closes, and SqlClient callbacks now run after the outermost transaction commits. SQL PersistedQueue settlements are fenced by acquisition. On the AI side, added the OpenAI safety identifier and prompt cache retention request options plus prompt cache breakpoints on image and file input, and fixed composed tool failure causes being lost and retry classification for provider response decoding failures. - Core, Schema & collections : The audit kept going with fixes for Cause.pretty on cyclic cause chains, Fiber.runIn and Effect.forkIn hanging, scoped forks running after scope closure, Effect.repeat turning a Done failure into a success, and Stream.retry slowing down on every retry. Defects now take precedence over typed failures in more recovery operators. Schema fixes cover Schema.Tuple encoding with omitted optional elements, Unicode casing checks, Schema.toFormatter and Schema.toTaggedUnion . Layers are now memoized by identity, and finite number and base64 validation run in linear time. - Config, CLI & parsers : Fixed YAML block scalars with tabs, Ini.parse dropping a trailing backslash, TOML empty quoted keys, Config.schema dropping record keys for non-string key schemas, OTEL RESOURCE ATTRIBUTES values containing = , and several CLI lexer edge cases with clustered short options. Also fixed DateTime.formatIsoDate for extended years, zoneFromString rejecting GMT , and nanosecond precision in Duration strings and inputs. You can follow the full changelog in the effect repository https://github.com/Effect-TS/effect/commits/main . To catch up on more updates, check out Effect v4 Updates https://www.effect.website/blog?category=effect-v4-updates , starting from the recently published Effect v4 RC: September 2026 Updates https://effect.website/blog/effect-v4-rc-september-recap . Other technical updates from the past week. - Render inherited CLI flags in their own help section with formatter collapse options https://github.com/Effect-TS/effect/pull/9276 Bug Fix, next-minor - Add schema-aware streaming CSV encoding and decoding https://github.com/Effect-TS/effect/pull/9291 Feature, next-minor - Expose migration-free encoded SQL message storage construction https://github.com/Effect-TS/effect/pull/9330 Feature, next-minor - Set column to undefined on CSV header errors https://github.com/Effect-TS/effect/pull/9427 Bug Fix, next-minor - Add Unhandled logging option to ignore combinators https://github.com/Effect-TS/effect/pull/9510 Bug Fix, next-minor - Report unobserved resource release defects https://github.com/Effect-TS/effect/pull/9388 Bug Fix, next-minor - Fix sql.insert and sql.updateValues crashing on an empty list https://github.com/Effect-TS/effect/pull/9453 Bug Fix, next-minor - Add Glob module and portable FileSystem.glob https://github.com/Effect-TS/effect/pull/9438 Feature, next-minor - Fix TOML inline tables and arrays being extended after definition https://github.com/Effect-TS/effect/pull/9537 Bug Fix, next-minor - Fix TOML multiline strings that end with quotes before the delimiter https://github.com/Effect-TS/effect/pull/9532 Bug Fix, next-minor - Detect unsupported FetchHttpClient streaming request bodies https://github.com/Effect-TS/effect/pull/9567 Bug Fix, next-minor - Replace effect/Crypto with per-family effect/crypto modules https://github.com/Effect-TS/effect/pull/9126 Feature, next-minor - Fix http : send stored cookies only to the matching host https://github.com/Effect-TS/effect/pull/9614 Bug Fix, next-minor - Add terminal resize stream https://github.com/Effect-TS/effect/pull/9639 Bug Fix, next-minor - Allow database clock lag in PersistedQueue SQL delay tests https://github.com/Effect-TS/effect/pull/9642 Bug Fix, next-minor - Add encrypted remote compaction to the event log https://github.com/Effect-TS/effect/pull/9571 Improvement, next-minor - Add McpTest in-memory client for McpServer registrations https://github.com/Effect-TS/effect/pull/9657 Feature, next-minor - Add opt-in RFC 9457 Problem Details to HttpApi https://github.com/Effect-TS/effect/pull/9706 Feature, next-minor - Add RpcServer onDisconnect option https://github.com/Effect-TS/effect/pull/9688 Bug Fix, next-minor - Fix Toml.parse accepting out of range dates and times https://github.com/Effect-TS/effect/pull/9648 Bug Fix, next-minor - Add request-aware visibility to McpServer https://github.com/Effect-TS/effect/pull/9661 Improvement, next-minor - Restore Anthropic spec fetching and schema regeneration https://github.com/Effect-TS/effect/pull/9509 Bug Fix, next-minor - Raise pnpm fetch timeout for large CI tarball downloads https://github.com/Effect-TS/effect/pull/9627 Bug Fix, next-minor - Wait for failure-suspended workflow activity replay in test https://github.com/Effect-TS/effect/pull/9456 Bug Fix, next-minor - Parameterize OpenAPI client with error/requirements generics https://github.com/Effect-TS/effect/pull/6402 Feature, next-minor - Fix opentelemetry : keep optional trace sdk peers out of the root entrypoint https://github.com/Effect-TS/effect/pull/9689 Bug Fix, next-minor - Bound synchronous Node readable and socket drains https://github.com/Effect-TS/effect/pull/9327 Bug Fix, next-minor - Add Glob module and portable FileSystem.glob https://github.com/Effect-TS/effect/pull/9438 Feature, next-minor - Replace effect/Crypto with per-family effect/crypto modules https://github.com/Effect-TS/effect/pull/9126 Feature, next-minor - Add terminal resize stream https://github.com/Effect-TS/effect/pull/9639 Bug Fix, next-minor - Default Bun idle timeouts to off and document streaming timeouts https://github.com/Effect-TS/effect/pull/9705 Bug Fix, next-minor - Fix sql-mssql : keep interrupted requests leased until Tedious settles them https://github.com/Effect-TS/effect/pull/9636 Bug Fix, next-minor - If you’re thinking of joining Effect Days 2026 https://effect.website/effect-days this December in Italy, you’d better hurry.Huge thanks to all our sponsors for helping us bring the Effect community together in Italy this December. 🤍 We're so happy to have you on board @zivergetech https://twitter.com/zivergetech @EffectfulTech https://twitter.com/EffectfulTech @warpdotco https://twitter.com/warpdotco @executorsh https://twitter.com/executorsh @academind real https://twitter.com/academind real @Cloudflare https://twitter.com/Cloudflare @novelcrafter https://twitter.com/novelcrafter effect.website/effect-days sp… https://effect.website/effect-days sponsors - All three Effect Miami speakers have been announced The meetup is scheduled for Nov 9. 🚀 Excited to announce John De Goes @jdegoes https://twitter.com/jdegoes as our main speaker for Effect Miami 3 It’s a real honor to welcome John, one of the most influential voices in modern functional programming. Creator of ZIO, founder of Ziverge, and Golem Cloud, his work has helped shape how we🚀 Excited to welcome 𝗛𝗮𝗿𝗿𝘆 𝗦𝗼𝗹𝗼𝘃𝗮𝘆 @harrysolovay https://twitter.com/harrysolovay to 𝗘𝗳𝗳𝗲𝗰𝘁 𝗠𝗶𝗮𝗺𝗶 𝟯 I first discovered Harry through his incredible hardcore TypeScript tutorials on YouTube. His depth of knowledge, creativity, and ability to push the boundaries of the type system🚀 Excited to welcome 𝗗𝗲𝘃𝗶𝗻 𝗝𝗮𝗺𝗲𝘀𝗼𝗻 @devinjameson https://twitter.com/devinjameson to 𝗘𝗳𝗳𝗲𝗰𝘁 𝗠𝗶𝗮𝗺𝗶 𝟯 Devin is the creator of @foldkit https://twitter.com/foldkit , an ambitious open-source frontend framework built on Effect and inspired by The Elm Architecture. Foldkit rethinks frontend development around - Effect Warsaw 2 https://luma.com/k5o7m2pg is coming up on November 17 Effect Warsaw 2 is coming next month 👉 Sam is going to talk about full stack effect. More talks, 🍕 and 🍻 coming too luma.com/k5o7m2pg https://luma.com/k5o7m2pg - Effect Office Hours 🔥 every Wednesday at 10:00 AM ET / 16:00 CET on our YouTube channel https://www.youtube.com/@effect-ts . Visit our Effect Community Events calendar https://luma.com/effect-community and subscribe for updates on upcoming Effect events. - Max at Cloudflare Connect @maxwellbrown https://twitter.com/maxwellbrown at cloudflare connect effect cluster on DOs - If we had a penny… i was wrong about effect when @schickling https://twitter.com/schickling bent my ear for an hour at next conf rip 2 years ago i told him it would never happen impossible nobody has time for all that because @EffectTS https://twitter.com/EffectTS is a lifestyle choice, developers resist change, it's too much surface area and - 💯 Opus 5.5 with @EffectTS https://twitter.com/EffectTS is the best combination ever - effect-api-query https://github.com/ueberBrot/effect-api-query - generate typed TanStack Query options and cache keys from Effect RPC and HTTP API contracts. By ueberBrot. - kabuki https://github.com/pkishorez/monorepo/tree/main/packages/kabuki - run your app as a tree of state-machine Actors outside React, built on Effect Schema, scoped Effects, and Layers. By pkishorez. - effect-snowflake https://github.com/RyanCallahan312/effect-extensions/tree/main/packages/effect-snowflake - an Effect v4 Snowflake client built on Apache Arrow ADBC, returning results as Arrow tables and record batches. By RyanCallahan312. - effect-mongodb https://github.com/doubleloop-io/effect-mongodb - Effect-based APIs for working with MongoDB. Version 0.8.0 is out and supports Effect v4. By doubleloop-io. We’re thrilled to announce Ziverge as the first Effect Adoption Partner Here are 3 things we're thrilled to announce, as part of our partnership with @EffectfulTech https://twitter.com/EffectfulTech , creators of @EffectTS https://twitter.com/EffectTS 🔥 ➡️ Ziverge will be sponsoring Effect Days ➡️ We have produced an Effect SDK for @GolemCloud https://twitter.com/GolemCloud ➡️ We've launched an @EffectTS https://twitter.com/EffectTS Training Workshop Sign up for Looking for a role where you can work with Effect? We now have a dedicated Effect jobs page featuring open roles from companies that use Effect. We’ll keep it updated as new opportunities come in. New this week: Bitfocus & Warp are hiring Effect engineers. Explore Effect job opportunities → https://www.effect.website/effect-jobs Disclaimer: Please note that these job postings are shared for informational purposes, and we encourage applicants to verify details directly with the hiring companies. Don’t forget to listen to our Cause & Effect podcast hosted by Johannes Schickling and available on YouTube https://www.youtube.com/@effect-ts , X Twitter https://x.com/EffectTS /status/2085682364315783506 , and audio platforms like Spotify https://open.spotify.com/episode/12L2neeIte6LUYQpzTh9n6 and Apple Podcast https://podcasts.apple.com/us/podcast/software-engineering-in-the-age-of-ai-10/id1781879869?i=1000780438320 . John A. De Goes, the creator of ZIO https://zio.dev/ , as well as CEO of Ziverge https://www.ziverge.com/ and Golem Cloud https://golem.cloud/ , joins Johannes Schickling and Michael Arnaldi to discuss how AI is reshaping software engineering, what developers should still learn, and why Effect’s primitives are especially valuable for coding agents. Play https://youtube.com/watch?v=irmz5X3c7Do - Effect Office Hours 51 🔥 Play https://youtube.com/watch?v=N0XcgJ khjM - Native Arbitraries, Schema Binary, and PostgreSQL | Office Hours 43 Play https://youtube.com/watch?v=7JbRfQQGMrg The Effect Merch Store https://effect.website/merch offers a selection of Effect-branded items designed for the community. All orders are processed and fully managed through Printful https://www.printful.com/ . Effect Merch is here We’re excited to announce the launch of our Effect merch page Grab your favorite swag & show your love for Effect in style 🧢 effect.website/merch https://effect.website/merch 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 Previous Module of the Week - Cluster, Part 4 https://effect.website/blog/module-of-the-week/cluster-idempotency