# Remix > Build and review Remix 3 applications using the `remix` npm package and subpath imports. Use when working on Remix app structure, routes, controllers, middleware, validation, data access, auth, sessions, file uploads, server setup, UI components, hydration, navigation, or tests. - Skill: `kentcdodds/remix` (Agent Skill, multi-file: 12 files) - Install (CLI): `npx skillmds@latest add kentcdodds/remix` - Raw SKILL.md: https://api.skillmd.com/api/skills/kentcdodds/remix/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: kentcdodds (https://skillmd.com/u/kentcdodds) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/kentcdodds/remix --- # Build a Remix App Use this skill for end-to-end Remix app work. It should help the agent choose the right layer first, reach for the right package, and avoid the most common Remix-specific mistakes. ## What Remix Is Remix 3 is a server-first web framework built on Web APIs such as `Request`, `Response`, `URL`, and `FormData`. All packages ship from a single npm package, `remix`, and are imported via subpath. There is no top-level `remix` import. A Remix app has four main pieces: - **Routes** in `app/routes.ts` define the typed URL contract and power `href()` generation. - **Controllers and actions** implement that contract and return `Response` objects. - **Middleware** composes request lifecycle behavior and populates typed context via `context.set(Key, value)`. - **Components** render UI with `remix/ui`. This is not React. A component receives a `handle`, reads current props from `handle.props`, and returns a render function. ## When To Use This Skill Use this skill for: - new features or refactors that touch routing, controllers, middleware, data, auth, sessions, UI, or tests - reviewing Remix app code for correctness, architecture, or framework usage - answering "how should this be structured in Remix?" questions - finding the right package, reference doc, or default pattern for a task ## Load Only The References You Need Classify the task first, then load the smallest useful reference set. Each reference file starts with a "What This Covers" section that lists the topics inside it — read that first to confirm the file is relevant before reading the rest. Use the table below to find candidates. Loading more than two or three files at once is usually a sign that the task hasn't been narrowed enough yet. | Task involves... | Start with | | ----------------------------------------------------------------------------- | ------------------------------------------- | | Defining URLs, writing controllers and actions, returning responses | `references/routing-and-controllers.md` | | Composing the request lifecycle, ordering middleware, bridging to a server | `references/middleware-and-server.md` | | Compiling and serving browser modules, asset URL namespaces, preloads | `references/assets-and-browser-modules.md` | | Parsing input, validating with schemas, defining tables, querying, migrations | `references/data-and-validation.md` | | Per-browser state, login flows, route protection, identity | `references/auth-and-sessions.md` | | Component setup, state, lifecycle, updates, `queueTask`, context | `references/component-model.md` | | Event handlers, styles, refs, click/key behavior, simple animations | `references/mixins-styling-events.md` | | `clientEntry`, `run`, ``, navigation, `` | `references/hydration-frames-navigation.md` | | Router tests, component tests, test isolation | `references/testing-patterns.md` | | Spring physics, tweens, layout transitions | `references/animate-elements.md` | | Authoring custom reusable mixins | `references/create-mixins.md` | Common bundles: - **Form or CRUD feature** -> routing, data and validation, testing; add auth if user-specific - **Protected area** -> auth and sessions, routing, testing - **Interactive widget** -> component model, mixins and styling; add hydration only if it runs in the browser - **Browser asset pipeline** -> assets and browser modules, hydration, middleware and server - **File upload** -> middleware and server, data and validation, testing - **Navigation or frames** -> hydration, frames, navigation ## Default Workflow 1. **Classify the change.** Decide whether it changes the route contract, request lifecycle, data model, auth or session behavior, or only UI. 2. **Start from the server contract.** Add or update `app/routes.ts` before wiring handlers or UI. 3. **Put code in the narrowest owner.** Favor route-local code first, then promote only when reuse is real. 4. **Make the server path correct before adding browser behavior.** A route should return the right `Response` via `router.fetch(...)` before you add `clientEntry(...)`, animations, or DOM effects. 5. **Add middleware deliberately.** Keep fast-exit middleware early and request-enriching middleware later. Export a typed `AppContext` from the root middleware stack and use it in controllers. 6. **Validate input at the boundary.** Parse and validate `Request`, `FormData`, params, cookies, and external payloads before they reach rendering or persistence logic. 7. **Hydrate only when necessary.** Prefer server-rendered UI. Use `clientEntry(...)` and `run(...)` only for real browser interactivity or browser-only APIs. 8. **Test the narrowest meaningful layer.** Prefer router tests for route behavior. Use component tests when the behavior is truly interactive or DOM-specific. 9. **Finish with verification.** Re-read the route flow, confirm auth and authorization boundaries, and run the smallest relevant test and typecheck loop. ## Project Layout Use these root directories consistently: - `app/` for runtime application code - `db/` for migrations and local database files - `public/` for static assets served as-is - `test/` for shared helpers, fixtures, and integration coverage - `tmp/` for uploads, caches, local session files, and other scratch data Inside `app/`, organize by responsibility: - `assets/` for client entrypoints and client-owned browser behavior - `controllers/` for route-owned handlers and route-local UI - `data/` for schema, queries, persistence setup, migrations, and runtime data initialization - `middleware/` for request lifecycle concerns such as auth, sessions, uploads, and database injection - `ui/` for shared cross-route UI primitives - `utils/` only for genuinely cross-layer helpers that do not clearly belong elsewhere - `routes.ts` for the route contract - `router.ts` for router setup and wiring ### Placement Precedence When code could live in multiple places: 1. Put it in the narrowest owner first. 2. If it belongs to one route, keep it with that route. 3. If it is shared UI across route areas, move it to `app/ui/`. 4. If it is request lifecycle setup, keep it in `app/middleware/`. 5. If it is schema, query, persistence, or startup data logic, keep it in `app/data/`. 6. Use `app/utils/` only as a last resort for truly cross-layer helpers. ### Route Ownership - Use a flat file in `app/controllers/` for a simple leaf action, such as `app/controllers/home.tsx` - Use a folder with `controller.tsx` when a route owns nested routes or multiple actions, such as `app/controllers/account/controller.tsx` - Mirror nested route structure on disk, such as `app/controllers/auth/login/controller.tsx` - Keep route-local UI next to its owner, such as `app/controllers/contact/page.tsx` - Move shared UI to `app/ui/` - If a flat leaf grows child routes or multiple actions, promote it to a controller folder ### Layout Anti-Patterns - Do not create `app/lib/` as a generic dumping ground - Do not create `app/components/` as a second shared UI bucket when `app/ui/` already owns that role - Do not put shared cross-route UI in `app/controllers/` - Do not put middleware or persistence helpers in `app/utils/` when they have a clearer home - Do not create folders for simple leaf actions unless they are real controllers ## Core Remix Rules - Import from `remix/`, never `import { ... } from 'remix'` - Treat `app/routes.ts` as the source of truth for URLs. Use `routes..href(...)` for redirects, links, tests, and internal URL construction - Controllers and actions should return explicit `Response` objects, including redirects, 404s, and validation failures. At the route boundary, prefer returning a `Response` for expected outcomes (validation errors, conflicts, not found) over throwing for control flow - Model HTTP behavior explicitly. Status codes, headers, redirects, cache rules, and content types are part of the route contract - Make the server route correct first. A POST should already return the right HTML, redirect, or error response on its own before `clientEntry(...)` layers interactivity on top - Validate input at the boundary using `remix/data-schema` (and `remix/data-schema/form-data` for forms). `parseSafe` makes the failure path a return value instead of an exception - Derive `AppContext` from the root middleware stack so `get(Database)`, `get(Session)`, `get(Auth)`, and similar keys stay typed. If the controller never reads from context, it doesn't need the harness - Outside actions and controllers, only use `getContext()` when `asyncContext()` is in the middleware stack - Remix Component is not React: read props from `handle.props`, keep state in setup-scope variables, call `handle.update()` explicitly, and do DOM-sensitive work in event handlers or `queueTask(...)`, not in render - Prefer host-element mixins via `mix={mixin(...)}` for behavior and styling instead of inventing custom host prop conventions. Use `mix={[...]}` only when composing multiple mixins - Hydrated `clientEntry(...)` props must be serializable. Do not pass functions, class instances, or opaque runtime objects ## Security And Session Defaults - Never ship demo secrets. In non-test environments, require session and provider secrets from the environment and fail fast if they are missing - Use hardened cookies: `httpOnly` always, `sameSite` by default, and `secure` when serving over HTTPS - Regenerate session IDs on login, logout, and privilege changes - Use `requireAuth()` to protect authenticated route areas, but still authorize resource ownership inside handlers and data writes - Add CSRF protection when browser forms mutate state using cookie-backed sessions - Add CORS only for endpoints that must be called cross-origin. Prefer same-origin by default - Prefer JSX or `remix/html-template` for HTML generation so escaping stays correct - Validate uploads for size, type, and destination. Treat filenames and content as untrusted input ## Testing Defaults - Prefer server and router tests first. Drive the app with `router.fetch(new Request(...))` and assert on the returned `Response` - Build a fresh router per test or per suite so sessions, in-memory storage, and database state stay isolated - Use `routes..href(...)` in tests so URLs stay coupled to the route contract - For auth or session scenarios, use a test cookie and `createMemorySessionStorage()` instead of production storage - Use component tests only for interactive or DOM-specific behavior. Render with `createRoot(...)`, interact with the real DOM, and call `root.flush()` between steps - Prefer one representative behavior test over many repetitive assertion variants ## Common Mistakes To Avoid - Treating Remix Component like React and reaching for hooks or implicit rerendering - Importing from a top-level `remix` entry instead of a subpath - Adding `clientEntry(...)` before the server-rendered route behavior is correct - Passing non-serializable props into `clientEntry(...)` - Calling `getContext()` without `asyncContext()` in the middleware stack - Getting middleware order wrong; fast exits like static files belong early, request enrichment later - Skipping boundary validation and trusting raw `FormData`, params, cookies, or external payloads - Letting route-local domain errors leak out of the controller. Translate expected outcomes (validation, conflicts, not-found) into the HTTP `Response` the route means to return rather than throwing a custom `Error` subclass and catching it elsewhere - Reaching for `createCookie` when a tamper-sensitive or server-managed per-browser fact really wants `remix/session`. If editing the value would be a bug, use a session - Building a JSON-only RPC layer when a normal form POST, redirect, or resource route would be simpler. Fetch-from-the-client is a layer on top of sound route behavior, not a replacement for it - Treating JSON state endpoints and `` reloads as mutually exclusive patterns. Pick the lightest sync mechanism that fits the UX; small widgets may reasonably poll a JSON endpoint - Assuming authentication is enough without per-resource authorization checks - Dropping shared code into vague buckets like `utils.ts`, `helpers.ts`, or `common.ts` when ownership is known - Writing only component tests for a feature whose main behavior is really an HTTP route concern ## Package Map Use this map to find the right package quickly. Each entry says what the package is for, not just what it exports. Open the linked reference file when you need full examples. ### Routing, Server, and Responses - `remix/router` — the router itself. Use for `createRouter`, controller and middleware types, and registering routes. A URL that matches a route pattern but not the request method gets `405 Method Not Allowed` with an `Allow` header (it does not reach `defaultHandler`); register an `ANY` route for a per-URL catch-all. `GET` routes also serve `HEAD` with the same status and headers and an empty body — do not add explicit `HEAD` routes just for that - `remix/routes` — declarative route builders. Use for `route`, `get`, `post`, `put`, `del`, `form`, `resources` when defining `app/routes.ts` - `remix/node-fetch-server` — adapter from Node's `http` module to a Fetch-style router. Use for `createRequestListener` in `server.ts` - `remix/assets` — browser asset server. Use for `createAssetServer` when serving compiled scripts and styles. Scripts resolve imports through import maps: read `getScriptEntry()` and render `` (from `remix/ui/server`) before the preloads and module script; use `fingerprint: true` (content hashes) plus `files.cacheKey` for persistent caches, and directory `mounts` (default `{ app, npm }`). Shared compiler options such as `target`, `sourceMaps`, `sourceMapSourcePaths`, and `minify` live at the top level. Kody's origin website does not use this: hydration URLs come from Pitlane `?assets=` - `remix/multiple-import-maps-polyfill` — `importModule()`, `detectMultipleImportMapSupport()`, `preloadShim()` for browsers without native multiple-import-map support. Only relevant with `remix/assets` - `remix/middleware/render` — pairs `createAssetServer` with frame rendering for Node apps. Do not use it on the origin Worker; Kody owns `renderToStream` plus Workers Assets - `remix/spa` — client-only `run(router)` for apps with no server document. Kody keeps a custom client router on top of server-rendered HTML: it runs the destination's loader before committing the URL, and route components read the payload through `createRouteData` (`#client/route-data.tsx`) so the previous page stays until the next one is ready — see `docs/contributing/no-flash-navigation.md` before adding a client route - `remix/headers` — typed header parsers and builders. Use when reading `Accept`, `Cookie`, or setting `CacheControl`, `Vary`, etc., instead of hand-formatting strings - `remix/response/redirect` — `redirect(href, status?)`. Use for the canonical "POST then redirect" pattern and other location changes - `remix/response/html` — `createHtmlResponse`. Use when you need an HTML `Response` from a string or stream without rendering through `remix/ui` - `remix/response/compress` — `compressResponse`. Use when compressing one-off responses outside the global `compression()` middleware - `remix/response/file` — file-download responses. Use for `Content-Disposition: attachment` responses - `remix/route-pattern` — low-level URL matching and generation. Use when working with raw patterns outside the router (custom matchers, scripts) - `remix/fetch-proxy` — Fetch-based HTTP proxying. Use to forward a request to another origin; pass `xForwardedHeaders` when the upstream needs forwarded proto, host, and port ### Data, Validation, and Persistence - `remix/data-schema` — schema builders for runtime validation. Use for `parse` and `parseSafe` to validate any input that crosses a trust boundary, and `.transform(...)` when validated output should map to a different value or type - `remix/data-schema/checks` — common check helpers (`email`, `minLength`, `maxLength`, etc.). Use to compose into a schema - `remix/data-schema/coerce` — coercion helpers for strings, numbers, booleans, dates, and ids. Use when input arrives as a string but should be a typed value - `remix/data-schema/form-data` — `f.object` and `f.field` for parsing `FormData` directly. Use in actions that read browser forms - `remix/data-table` — typed tables and a `Database` interface. Use for `table`, `column`, and `new Database(driver)` when modeling persisted data - `remix/data-table/sqlite`, `remix/data-table/postgres`, `remix/data-table/mysql` — official drivers. Use `createSqliteDatabase(...)` for Node, Bun, and compatible synchronous SQLite clients. Remix does not ship a D1 factory; Kody owns `D1DatabaseDriver` and passes it to `new Database` - `remix/data-table/migrations` — migration authoring and runners. Use for `createMigration`, `createMigrationRunner` - `remix/data-table/migrations/node` — `loadMigrations` from disk. Use in startup scripts that apply migrations - `remix/data-table/operators` — query operators such as `inList(...)`. Use when `where` clauses need set or comparison logic ### Auth, Sessions, and Cookies - `remix/session` — the `Session` object: `get`, `set`, `flash`, `unset`, `regenerateId`. Use for any per-browser state where tampering would be a bug (login, "I submitted this form already", cart, flash messages) - `remix/middleware/session` — `session(cookie, storage)`. Use to wire a session cookie and storage backend into the root middleware stack - `remix/session-storage/fs`, `remix/session-storage/memory`, `remix/session-storage/cookie` — storage backends. Use `fs-storage` for single-process apps, `memory-storage` for tests, `cookie-storage` for stateless deployments where data fits in a cookie - `remix/session-storage/redis` — Redis-backed storage. Use for multi-process or multi-host deployments - `remix/session-storage/memcache` — Memcache-backed storage. Same multi-host use case as Redis - `remix/cookie` — `createCookie` for plain signed/unsigned cookies. Use for non-sensitive preferences where the client is allowed to control the value (theme, locale, dismissed banner). For state where tampering matters, prefer `remix/session` - `remix/auth` — credentials, OAuth, and OIDC providers. Use to define how identity is verified, start/finish external login, and refresh stored OAuth/OIDC token bundles with `refreshExternalAuth(...)`. Use `OAuthTokens`. There is no built-in Atmosphere/atproto provider. - `remix/middleware/auth` — `auth({ schemes })`, `requireAuth`, the `Auth` context key. Use to resolve identity into the request context and to gate routes ### UI, Hydration, and Browser Behavior - `remix/ui` — the component runtime: components, core mixins, `clientEntry`, `run`, ``, navigation helpers, and `createRoot`. Use for app UI behavior. Framework attributes are `data-rmx-*` (`data-rmx-target`, `data-rmx-document`, `data-rmx-history`, …). Listen with native `target.addEventListener(type, listener, { signal })`; there is no `addEventListeners()` helper. Server-rendered `