diff --git a/packages/app/index.html b/packages/app/index.html
index d71535182c81..c772f86209af 100644
--- a/packages/app/index.html
+++ b/packages/app/index.html
@@ -7,11 +7,11 @@
       content="width=device-width, initial-scale=1, interactive-widget=resizes-content, viewport-fit=cover"
     />
     <title>OpenCode</title>
-    <link rel="icon" type="image/png" href="/favicon-96x96-v3.png" sizes="96x96" />
-    <link rel="icon" type="image/svg+xml" href="/favicon-v3.svg" />
-    <link rel="shortcut icon" href="/favicon-v3.ico" />
-    <link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon-v3.png" />
-    <link rel="manifest" href="/site.webmanifest" />
+    <link rel="icon" type="image/png" href="favicon-96x96-v3.png" sizes="96x96" />
+    <link rel="icon" type="image/svg+xml" href="favicon-v3.svg" />
+    <link rel="shortcut icon" href="favicon-v3.ico" />
+    <link rel="apple-touch-icon" sizes="180x180" href="apple-touch-icon-v3.png" />
+    <link rel="manifest" href="site.webmanifest" />
     <meta name="theme-color" content="#fafafa" />
     <meta name="mobile-web-app-capable" content="yes" />
     <meta name="apple-mobile-web-app-capable" content="yes" />
@@ -19,6 +19,7 @@
     <meta property="og:image" content="/social-share.png" />
     <meta property="twitter:image" content="/social-share.png" />
     <script id="oc-theme-preload-script" src="/oc-theme-preload.js"></script>
+    <script id="oc-base-path" type="application/json">/</script>
   </head>
   <body class="antialiased overscroll-none text-12-regular overflow-hidden bg-v2-background-bg-deep">
     <noscript>You need to enable JavaScript to run this app.</noscript>
diff --git a/packages/app/src/app.tsx b/packages/app/src/app.tsx
index 4ab0a95c23e0..8e2fa92b24f4 100644
--- a/packages/app/src/app.tsx
+++ b/packages/app/src/app.tsx
@@ -467,6 +467,7 @@ export function AppInterface(props: {
   servers?: Array<ServerConnection.Any>
   router?: Component<BaseRouterProps>
   disableHealthCheck?: boolean
+  basePath?: string
 }) {
   // The visual new layout lives in the router root so it remains mounted across
   // route changes. Draft and session routes override only their server-bound data
@@ -492,6 +493,7 @@ export function AppInterface(props: {
             <Show when={useSettings().general.newLayoutDesigns().toString()} keyed>
               <Dynamic
                 component={props.router ?? Router}
+                base={props.basePath || undefined}
                 root={(routerProps) => (
                   <TabsProvider>
                     <NotificationProvider>
diff --git a/packages/app/src/entry.tsx b/packages/app/src/entry.tsx
index c41c1bb4b63e..929ea19c986d 100644
--- a/packages/app/src/entry.tsx
+++ b/packages/app/src/entry.tsx
@@ -99,11 +99,33 @@ if (!(root instanceof HTMLElement) && import.meta.env.DEV) {
   throw new Error(getRootNotFoundError())
 }
 
+/**
+ * Read the runtime base path injected by the server into the <script
+ * id="oc-base-path" type="application/json"> tag. This allows the frontend to
+ * know its mount point (e.g. "/opencode/") without a rebuild — the server
+ * rewrites the tag content on every response.
+ *
+ * Returns "" when the app is served from "/" (the common case), so that
+ * concatenation with origin yields a clean URL.
+ */
+const getBasePath = () => {
+  const el = document.getElementById("oc-base-path")
+  if (!el?.textContent) return ""
+  try {
+    const raw = JSON.parse(el.textContent) as string
+    // Normalize: ensure leading slash, no trailing slash, or empty for root
+    if (raw === "/" || !raw) return ""
+    return `/${raw.replace(/^\/+|\/+$/g, "")}`
+  } catch {
+    return ""
+  }
+}
+
 const getCurrentUrl = () => {
   if (location.hostname.includes("opencode.ai")) return "http://localhost:4096"
   if (import.meta.env.DEV)
     return `http://${import.meta.env.VITE_OPENCODE_SERVER_HOST ?? "localhost"}:${import.meta.env.VITE_OPENCODE_SERVER_PORT ?? "4096"}`
-  return location.origin
+  return location.origin + getBasePath()
 }
 
 const getDefaultUrl = () => {
@@ -173,6 +195,7 @@ if (root instanceof HTMLElement) {
             canonicalLocalServer={ServerConnection.key(server)}
             servers={[server]}
             disableHealthCheck
+            basePath={getBasePath() || undefined}
           />
         </AppBaseProviders>
       </PlatformProvider>
diff --git a/packages/opencode/src/cli/cmd/web.ts b/packages/opencode/src/cli/cmd/web.ts
index 69a981aada49..7c1ace906a84 100644
--- a/packages/opencode/src/cli/cmd/web.ts
+++ b/packages/opencode/src/cli/cmd/web.ts
@@ -42,13 +42,14 @@ export const WebCommand = effectCmd({
     }
     const opts = yield* resolveNetworkOptions(args)
     const server = yield* Effect.promise(() => Server.listen(opts))
+    const basePath = opts.basePath?.replace(/\/+$/, "") || ""
     UI.empty()
     UI.println(UI.logo("  "))
     UI.empty()
 
     if (opts.hostname === "0.0.0.0") {
       // Show localhost for local access
-      const localhostUrl = `http://localhost:${server.port}`
+      const localhostUrl = `http://localhost:${server.port}${basePath}`
       UI.println(UI.Style.TEXT_INFO_BOLD + "  Local access:      ", UI.Style.TEXT_NORMAL, localhostUrl)
 
       // Show network IPs for remote access
@@ -58,7 +59,7 @@ export const WebCommand = effectCmd({
           UI.println(
             UI.Style.TEXT_INFO_BOLD + "  Network access:    ",
             UI.Style.TEXT_NORMAL,
-            `http://${ip}:${server.port}`,
+            `http://${ip}:${server.port}${basePath}`,
           )
         }
       }
@@ -67,14 +68,14 @@ export const WebCommand = effectCmd({
         UI.println(
           UI.Style.TEXT_INFO_BOLD + "  mDNS:              ",
           UI.Style.TEXT_NORMAL,
-          `${opts.mdnsDomain}:${server.port}`,
+          `${opts.mdnsDomain}:${server.port}${basePath}`,
         )
       }
 
       // Open localhost in browser
       open(localhostUrl).catch(() => {})
     } else {
-      const displayUrl = server.url.toString()
+      const displayUrl = server.url.toString() + basePath
       UI.println(UI.Style.TEXT_INFO_BOLD + "  Web interface:    ", UI.Style.TEXT_NORMAL, displayUrl)
       open(displayUrl).catch(() => {})
     }
diff --git a/packages/opencode/src/cli/network.ts b/packages/opencode/src/cli/network.ts
index 22040ed41015..7467654e07aa 100644
--- a/packages/opencode/src/cli/network.ts
+++ b/packages/opencode/src/cli/network.ts
@@ -30,6 +30,11 @@ const options = {
     describe: "additional domains to allow for CORS",
     default: [] as string[],
   },
+  "base-path": {
+    type: "string" as const,
+    describe: "base path for the web UI (e.g., /opencode/)",
+    default: "/",
+  },
 }
 
 export type NetworkOptions = InferredOptionTypes<typeof options>
@@ -75,6 +80,7 @@ export function resolveNetworkOptionsNoConfig(args: NetworkOptions, config?: Con
   const configCors = config?.server?.cors ?? []
   const argsCors = Array.isArray(args.cors) ? args.cors : args.cors ? [args.cors] : []
   const cors = [...configCors, ...argsCors]
+  const basePath = args["base-path"] ?? "/"
 
-  return { hostname, port, mdns, mdnsDomain, cors }
+  return { hostname, port, mdns, mdnsDomain, cors, basePath }
 }
diff --git a/packages/opencode/src/server/routes/instance/httpapi/server.ts b/packages/opencode/src/server/routes/instance/httpapi/server.ts
index 61e8df7d11fc..8f0ddd07ed61 100644
--- a/packages/opencode/src/server/routes/instance/httpapi/server.ts
+++ b/packages/opencode/src/server/routes/instance/httpapi/server.ts
@@ -191,16 +191,22 @@ const docRoute = HttpRouter.use((router) => router.add("GET", "/doc", () => Effe
   Layer.provide(authOnlyRouterLayer),
 )
 
-const uiRoute = HttpRouter.use((router) =>
-  Effect.gen(function* () {
-    const fs = yield* FSUtil.Service
-    const client = yield* HttpClient.HttpClient
-    const flags = yield* RuntimeFlags.Service
-    yield* router.add("*", "/*", (request) =>
-      serveUIEffect(request, { fs, client, disableEmbeddedWebUi: flags.disableEmbeddedWebUi }),
-    )
-  }),
-).pipe(Layer.provide(authOnlyRouterLayer))
+const uiRoute = (basePath: string) =>
+  HttpRouter.use((router) =>
+    Effect.gen(function* () {
+      const fs = yield* FSUtil.Service
+      const client = yield* HttpClient.HttpClient
+      const flags = yield* RuntimeFlags.Service
+      yield* router.add("*", "/*", (request) =>
+        serveUIEffect(request, {
+          fs,
+          client,
+          disableEmbeddedWebUi: flags.disableEmbeddedWebUi,
+          basePath,
+        }),
+      )
+    }),
+  ).pipe(Layer.provide(authOnlyRouterLayer))
 
 type RouteRequirements =
   | HttpRouter.HttpRouter
@@ -270,6 +276,7 @@ const app = LayerNode.group([
 
 export function createRoutes(
   corsOptions?: CorsOptions,
+  basePath: string = "/",
 ): Layer.Layer<never, EffectConfig.ConfigError, RouteRequirements> {
   const locationServiceMapV2 = buildLocationServiceMap()
 
@@ -280,7 +287,7 @@ export function createRoutes(
     instanceRoutes,
     serverRoutes,
     docRoute,
-    uiRoute,
+    uiRoute(basePath),
   ).pipe(
     Layer.provide([
       errorLayer,
diff --git a/packages/opencode/src/server/server.ts b/packages/opencode/src/server/server.ts
index 440b992c1557..966042115745 100644
--- a/packages/opencode/src/server/server.ts
+++ b/packages/opencode/src/server/server.ts
@@ -34,6 +34,7 @@ type ListenOptions = CorsOptions & {
   hostname: string
   mdns?: boolean
   mdnsDomain?: string
+  basePath?: string
 }
 type ListenerState = {
   scope: Scope.Scope
@@ -98,7 +99,7 @@ const listenEffect: (opts: ListenOptions) => Effect.Effect<EffectListener, unkno
 )
 
 function listenerLayer(opts: ListenOptions, port: number) {
-  return HttpRouter.serve(HttpApiApp.createRoutes(opts), {
+  return HttpRouter.serve(HttpApiApp.createRoutes(opts, opts.basePath ?? "/"), {
     middleware: disposeMiddleware,
     disableLogger: true,
     disableListenLog: true,
diff --git a/packages/opencode/src/server/shared/ui.ts b/packages/opencode/src/server/shared/ui.ts
index c2fd3b86375c..812c28753532 100644
--- a/packages/opencode/src/server/shared/ui.ts
+++ b/packages/opencode/src/server/shared/ui.ts
@@ -52,11 +52,28 @@ function notFound() {
   return HttpServerResponse.jsonUnsafe({ error: "Not Found" }, { status: 404 })
 }
 
-function embeddedUIResponse(file: string, body: Uint8Array) {
+/**
+ * Inject the runtime base path into the HTML so the client can read it before
+ * the JS bundle executes. The `oc-base-path` script tag in index.html holds a
+ * JSON-encoded path (defaulting to "/"); here we replace its content with the
+ * configured base path so the frontend knows its mount point without needing a
+ * rebuild.
+ */
+function injectBasePath(html: string, basePath: string): string {
+  const normalized = basePath === "/" ? "/" : `/${basePath.replace(/^\/+|\/+$/g, "")}/`
+  return html.replace(
+    /(<script\s+id="oc-base-path"[^>]*>)([\s\S]*?)(<\/script>)/i,
+    `$1${JSON.stringify(normalized)}$3`,
+  )
+}
+
+function embeddedUIResponse(file: string, body: Uint8Array, basePath: string) {
   const mime = FSUtil.mimeType(file)
   const headers = new Headers({ "content-type": mime })
   if (mime.startsWith("text/html")) {
-    headers.set("content-security-policy", cspForHtml(new TextDecoder().decode(body)))
+    const html = injectBasePath(new TextDecoder().decode(body), basePath)
+    headers.set("content-security-policy", cspForHtml(html))
+    return HttpServerResponse.text(html, { headers })
   }
   return HttpServerResponse.raw(body, { headers })
 }
@@ -65,25 +82,27 @@ export function serveEmbeddedUIEffect(
   requestPath: string,
   fs: FSUtil.Interface,
   embeddedWebUI: Record<string, string>,
+  basePath: string = "/",
 ) {
   const file = embeddedWebUI[requestPath.replace(/^\//, "")] ?? embeddedWebUI["index.html"] ?? null
   if (!file) return Effect.succeed(notFound())
 
   return fs.readFile(file).pipe(
-    Effect.map((body) => embeddedUIResponse(file, body)),
+    Effect.map((body) => embeddedUIResponse(file, body, basePath)),
     Effect.catchReason("PlatformError", "NotFound", () => Effect.succeed(notFound())),
   )
 }
 
 export function serveUIEffect(
   request: HttpServerRequest.HttpServerRequest,
-  services: { fs: FSUtil.Interface; client: HttpClient.HttpClient; disableEmbeddedWebUi: boolean },
+  services: { fs: FSUtil.Interface; client: HttpClient.HttpClient; disableEmbeddedWebUi: boolean; basePath?: string },
 ) {
+  const basePath = services.basePath ?? "/"
   return Effect.gen(function* () {
     const embeddedWebUI = yield* Effect.promise(() => embeddedUI(services.disableEmbeddedWebUi))
     const path = new URL(request.url, "http://localhost").pathname
 
-    if (embeddedWebUI) return yield* serveEmbeddedUIEffect(path, services.fs, embeddedWebUI)
+    if (embeddedWebUI) return yield* serveEmbeddedUIEffect(path, services.fs, embeddedWebUI, basePath)
 
     const response = yield* services.client.execute(
       HttpClientRequest.make(request.method)(upstreamURL(path), {
@@ -94,7 +113,7 @@ export function serveUIEffect(
     const headers = proxyResponseHeaders(response.headers)
 
     if (response.headers["content-type"]?.includes("text/html")) {
-      const body = yield* response.text
+      const body = injectBasePath(yield* response.text, basePath)
       headers.set("Content-Security-Policy", cspForHtml(body))
       return HttpServerResponse.text(body, { status: response.status, headers })
     }
