diff --git a/.env.example b/.env.example
index ebdf694..b54a7d4 100644
--- a/.env.example
+++ b/.env.example
@@ -30,6 +30,13 @@ APPLE_CLIENT_ID=
 APPLE_TEAM_ID=
 APPLE_KEY_ID=
 
+# Local development sign-in. Set an address here and a `dev` provider appears
+# that signs you in as that user without contacting Google, GitHub or Apple, so
+# a checkout can be run end to end without registering an OAuth application.
+# It is ignored unless NODE_ENV is `dev`, and `central:start` hardcodes prod.
+# DEV_AUTH_EMAIL=you@example.com
+# DEV_AUTH_NAME=Local Developer
+
 # ── Relay (DB-free WebSocket relay) ───────────────────────────────────────────
 RELAY_HOST=127.0.0.1
 RELAY_PORT=6970
diff --git a/central/auth/providers.ts b/central/auth/providers.ts
index e6ed915..c30d331 100644
--- a/central/auth/providers.ts
+++ b/central/auth/providers.ts
@@ -11,8 +11,14 @@ import {
   saveLoginState,
 } from "./store";
 
-const PROVIDERS = ["google", "github", "apple"] as const;
+const PROVIDERS = ["google", "github", "apple", "dev"] as const;
 const APPLE_PRIVATE_KEY_FILE = "apple_key.p8";
+/**
+ * Placeholder in the `code` slot of the dev provider's callback. The dev flow
+ * carries no provider code, but the callback route requires a non-empty one,
+ * and the value that actually matters is the single-use `state`.
+ */
+const DEV_AUTHORIZATION_CODE = "dev";
 
 type ProviderStatus = {
   id: AuthProvider;
@@ -28,7 +34,12 @@ type AppleUser = {
 };
 
 export function listProviders(): ProviderStatus[] {
-  return PROVIDERS.map((id) => ({ id, enabled: isProviderEnabled(id) }));
+  return PROVIDERS.map((id) => ({ id, enabled: isProviderEnabled(id) })).filter(
+    // The dev provider is an artefact of a local checkout, not a sign-in option
+    // users should ever hear about. Omitting it while disabled keeps this
+    // response byte-identical to what a production instance returned before.
+    (provider) => provider.id !== "dev" || provider.enabled,
+  );
 }
 
 export function isProviderEnabled(provider: AuthProvider): boolean {
@@ -44,6 +55,11 @@ export function isProviderEnabled(provider: AuthProvider): boolean {
           env.APPLE_KEY_ID &&
           hasApplePrivateKey(),
       );
+    case "dev":
+      // Two independent gates. NODE_ENV is set by the start script rather than
+      // by .env (`central:start` hardcodes prod), so a production instance
+      // cannot switch this on through configuration alone.
+      return env.NODE_ENV === "dev" && Boolean(env.DEV_AUTH_EMAIL);
   }
 }
 
@@ -84,6 +100,22 @@ function createOAuthAuthorizationUrl(
   ensureProviderEnabled(provider);
   const state = arctic.generateState();
 
+  if (provider === "dev") {
+    saveLoginState(state, provider, {
+      callbackUrl: options.callbackUrl,
+      purpose: options.purpose,
+      userId: options.userId,
+    });
+    // There is no external authorization server to visit, so the
+    // "authorization URL" is our own callback. Everything downstream of the
+    // callback (state consumption, exchange codes, browser cookies, deep
+    // links) is then the same code path every real provider takes.
+    const url = new URL(callbackUrl("dev"));
+    url.searchParams.set("code", DEV_AUTHORIZATION_CODE);
+    url.searchParams.set("state", state);
+    return url.toString();
+  }
+
   if (provider === "google") {
     const codeVerifier = arctic.generateCodeVerifier();
     saveLoginState(state, provider, {
@@ -131,6 +163,23 @@ export async function getProfileFromCallback(
   ensureProviderEnabled(provider);
   const loginState = consumeLoginState(state, provider);
 
+  if (provider === "dev") {
+    const email = required(env.DEV_AUTH_EMAIL, "DEV_AUTH_EMAIL");
+    return {
+      loginState,
+      profile: {
+        provider,
+        // Derived from the address so that changing DEV_AUTH_EMAIL yields a
+        // different account rather than renaming the existing one.
+        providerAccountId: `dev:${email.toLowerCase()}`,
+        email,
+        emailVerified: true,
+        name: env.DEV_AUTH_NAME ?? "Local Developer",
+        avatarUrl: null,
+      },
+    };
+  }
+
   if (provider === "google") {
     if (!loginState.codeVerifier) {
       throw new BadRequestError("Invalid sign-in request.");
diff --git a/central/auth/store.ts b/central/auth/store.ts
index 2d22d55..d0e6283 100644
--- a/central/auth/store.ts
+++ b/central/auth/store.ts
@@ -7,7 +7,7 @@ import {
 import { nanoid } from "nanoid";
 import { createToken, hashToken } from "./crypto";
 
-export type AuthProvider = "google" | "github" | "apple";
+export type AuthProvider = "google" | "github" | "apple" | "dev";
 
 export type AuthLinkedAccount = {
   provider: AuthProvider;
diff --git a/central/env.ts b/central/env.ts
index f0c2358..b7c0424 100644
--- a/central/env.ts
+++ b/central/env.ts
@@ -30,6 +30,14 @@ const envSchema = sharedEnvSchema.extend({
   APPLE_CLIENT_ID: z.string().optional(),
   APPLE_TEAM_ID: z.string().optional(),
   APPLE_KEY_ID: z.string().optional(),
+  /**
+   * Enables the `dev` sign-in provider, which signs in as this address without
+   * contacting any external identity provider. Ignored unless NODE_ENV is
+   * `dev`, so setting it on a production instance does nothing.
+   */
+  DEV_AUTH_EMAIL: z.email().optional(),
+  /** Display name for the `dev` provider's user. */
+  DEV_AUTH_NAME: z.string().optional(),
 });
 
 export const env = envSchema.parse(process.env);
diff --git a/docs/oauth-flow.md b/docs/oauth-flow.md
index d7de12e..7b4e795 100644
--- a/docs/oauth-flow.md
+++ b/docs/oauth-flow.md
@@ -21,6 +21,14 @@ Provider settings:
 
 For Apple, the private key is the PKCS#8 `.p8` file from Apple Developer. Place it at `server/apple_key.p8`; this file is ignored by git and read directly by the server.
 
+### Local development without an OAuth application
+
+Registering a Google, GitHub or Apple application is a prerequisite for signing in at all, which makes a fresh checkout impossible to run end to end. For that case there is a fourth provider, `dev`.
+
+Set `DEV_AUTH_EMAIL` (and optionally `DEV_AUTH_NAME`) and a `dev` entry appears in `GET /auth/providers`. Choosing it signs you in as that address: no external identity provider is contacted, the "authorization URL" is the server's own callback, and everything after the callback (single-use state, exchange codes, browser cookies, deep links) is the same code path the real providers take. The account is upserted by email like any other, so it behaves as a normal user afterwards.
+
+Two independent gates keep it out of production. It is enabled only when `NODE_ENV` is `dev`, which the `central:start` script hardcodes to `prod`, and only when `DEV_AUTH_EMAIL` is set. While disabled it is omitted from `GET /auth/providers` entirely, so a production response is unchanged. Note that `NODE_ENV=dev` already relaxes host verification, CORS and the trusted-web-origin check, so an instance running in that mode was never safe to expose; this provider does not widen that.
+
 Provider redirect URLs to register:
 
 - Google: `{AUTH_PUBLIC_BASE_URL}/auth/oauth/google/callback`
diff --git a/readme.md b/readme.md
index c8029a6..7c551c3 100644
--- a/readme.md
+++ b/readme.md
@@ -62,6 +62,8 @@ pnpm run relay:pm2:restart
 
 See [docs/oauth-flow.md](docs/oauth-flow.md) for provider setup, token lifecycle, and the app/WebSocket authentication flow.
 
+To run a checkout end to end without registering an OAuth application, set `DEV_AUTH_EMAIL` in `.env`. A `dev` provider then appears and signs you in as that address. It is ignored unless `NODE_ENV` is `dev`.
+
 ## App WebSocket Authentication
 
 The app no longer sends access tokens or device metadata in the `/app` WebSocket URL. Instead: