trpc

tRPC v11

The decisions tRPC forces and how to settle them, written so an agent applies them while writing or reviewing code. Every rule names the wrong default it corrects; there is no rule for what the model already gets right.

Pinned to tRPC v11, verified against `11.18.0` (2026-06-17). There is no v12 — but several APIs here carry @deprecated … will be removed in v12 and still ship today. Peers: typescript >=5.7.2, @tanstack/react-query ^5.80.3, react >=18.2.0.

When to Apply

Use this skill when:

• Code imports initTRPC, createTRPCContext, createTRPCOptionsProxy, createTRPCReact, createTRPCClient, httpBatchLink, httpSubscriptionLink, splitLink, fetchRequestHandler, createCallerFactory, or TRPCError — or defines procedures with .input() / .output() / .use() / .query() / .mutation() / .subscription()
• The user says "everything types as any", "invalidation isn't working", "contextMap[utilName] is not a function", "the transformer property moved", "414 / 413 on the dashboard", "subscriptions won't connect", "the prefetch isn't hydrating", or "it 404s every procedure"
• Migrating a codebase from tRPC v10, or reviewing tRPC code written against v10-era examples — the highest-yield moment, because the recommended React client changed and stale code often still compiles
• Adding the first subscription, the first file upload, or the first RSC prefetch to an existing router — each crosses into a surface where v11 replaced the v10 approach outright
• Reviewing a batched client as the app grows, where the uncapped defaults turn into intermittent production failures

This skill is NOT for:

• General TanStack Query semantics — cache lifetimes, retry, useMutation ergonomics (→ tanstack-query)
• Authoring or migrating the Zod schemas used as validators (→ zod)
• Next.js App Router routing, streaming, or caching beyond the tRPC handler (→ nextjs)
• General TypeScript narrowing and generics (→ typescript)

Rule Categories

Quick Reference

1. React Client Surface

• `client-tanstack-integration` — Build React data fetching on @trpc/tanstack-react-query; createTRPCReact is now the classic path
• `client-invalidate-with-query-filters` — useUtils() does not exist on the new proxy; invalidate via queryClient + pathFilter() / queryFilter()
• `client-derive-query-keys` — getQueryKey() is not on the new proxy; keys come off it as queryKey() / pathKey() / infiniteQueryKey()
• `client-subscription-options` — .useSubscription() is not on the new proxy; feed subscriptionOptions() to useSubscription from @trpc/tanstack-react-query

2. v10 → v11 Drift

• `mig-formdata-is-native` — All six experimental_* upload APIs were removed; FormData is a native input behind a splitLink
• `mig-renamed-type-exports` — AnyRouter → AnyTRPCRouter and friends; inferRouterInputs/Outputs did not change
• `mig-await-get-raw-input` — rawInput is undefined; inputs are lazy, so await getRawInput()
• `mig-typescript-version-floor` — TS >=5.7.2, and an editor on a different TS silently types everything as any

3. Router & Procedure Construction

• `proc-narrow-ctx-in-middleware` — Bare next() leaves ctx.user nullable, so the guard gets cast away with !
• `proc-input-before-use` — .use() before .input() runs middleware against unvalidated input
• `proc-single-trpc-instance` — One initTRPC.create() per app; mismatched instances make mergeRouters throw at runtime
• `proc-merge-only-object-inputs` — Only object schemas merge; anything else silently replaces the earlier parser
• `proc-concat-over-standalone-middleware` — experimental_standaloneMiddleware is deprecated and cannot declare .input(); use .concat()

4. Error & Validation Semantics

• `err-format-standard-schema-issues` — Parser dispatch is ordered, so a Zod-only errorFormatter returns null for Valibot / Effect (StandardSchemaV1Error) and for ArkType (ArkErrors)
• `err-output-strips-fields` — .output() returns the parsed value, so it strips unknown keys; its failure is a 500, not a 4xx
• `err-nullish-cursor` — .optional() cursors 400 only after an invalidate; use .nullish()
• `err-set-isdev-explicitly` — Without an explicit isDev, edge runtimes ship error.data.stack to every client

5. Links, Transport & Serialization

• `link-transformer-on-terminating-links` — The transformer moved into the link; deleting it to clear the branded type error breaks Date at runtime
• `link-route-subscriptions-separately` — httpBatchLink rejects subscription operations outright
• `link-cap-batch-size` — maxItems and maxURLLength default to Infinity; pair them with the server's maxBatchSize
• `link-gate-cache-headers` — Batching plus blanket responseMeta caching lets a CDN serve one user's data to another
• `link-default-to-httpbatchlink` — httpBatchStreamLink cannot set response headers once streaming; it is not the default
• `link-read-batch-headers-from-oplist` — Batch links pass { opList }, not { op }; destructuring wrong makes every request 401
• `link-scope-body-parsers` — A global express.json() drains the stream before tRPC reads it
• `link-endpoint-matches-mount-path` — endpoint is the prefix tRPC strips; a mismatch 404s every procedure

6. SSR, RSC & Server-Side Calls

• `rsc-query-client-per-request` — A module-scope QueryClient serves one user's cache to the next request
• `rsc-dehydrate-pending-queries` — Without the pending override, void prefetchQuery never reaches the client
• `rsc-prefetch-through-options-proxy` — Caller results never enter the cache, so the client fetches it all again
• `rsc-share-logic-not-callers` — A nested caller re-creates context and re-runs the whole middleware chain

7. Subscriptions & Streaming

• `sub-write-async-generators` — observable() is deprecated for removal, and only generators get tracked() reconnect-and-resume
• `sub-keep-credentials-out-of-urls` — connectionParams serializes tokens into the query string, and into every log that sees it
• `sub-enable-sse-keepalive` — ping.enabled is false by default, so idle SSE streams get reaped by proxies and read as a flaky network
• `sub-attach-listener-before-backlog` — Fetching history before attaching the listener drops events only under production load

How to Use

Read a reference file when its decision comes up. Each rule names the wrong default it corrects, then shows the canonical way — with an incorrect/correct contrast only where the wrong way is a real trap.

Two shortcuts worth taking first:

• Reviewing or migrating existing tRPC code? Start with client- and mig-. Stale code frequently still compiles, so nothing points you at these; they are what everything else inherits.
• Hardening something already working? The security-shaped rules are link-gate-cache-headers, rsc-query-client-per-request, err-set-isdev-explicitly, proc-input-before-use, and sub-keep-credentials-out-of-urls.

• Section definitions — category structure and ordering rationale
• Rule template — for adding new rules
• AGENTS.md — auto-built table of contents across all rules

Related Skills

• `tanstack-query` — The query layer tRPC's React client now delegates to; owns cache semantics this skill assumes
• `zod` — Validator authoring and Zod 4 drift, including the .flatten() → z.treeifyError() change this skill only points at
• `typescript` — General type-level work beyond tRPC's inference surface