diff --git a/api/deno.json b/api/deno.json
index 604b180..b93b346 100644
--- a/api/deno.json
+++ b/api/deno.json
@@ -4,7 +4,7 @@
     "@std/http": "jsr:@std/http@^1.0.22"
   },
   "name": "@01edu/api",
-  "version": "0.1.6",
+  "version": "0.1.7",
   "license": "MIT",
   "exports": {
     "./context": "./context.ts",
diff --git a/api/env.ts b/api/env.ts
index 9f78843..4208392 100644
--- a/api/env.ts
+++ b/api/env.ts
@@ -128,6 +128,31 @@ const forAppEnv =
  * ```
  */
 export const PROD: EnvGetter = forAppEnv('prod')
+
+/**
+ *
+ * The root for all relative URLs will be this BASE_URL, so it should start and end with a slash.
+ * If base URL is not set, it defaults to '/', which means the app is served at the root of the domain.
+ * If the current application is deployed at https://domain.com/tournament/, with <base href="/tournament/" />
+ * <a href="dashboard"> will point to https://domain.com/tournament/dashboard
+ *
+ * @example
+ * ```ts
+ * import { BASE_URL } from '@01edu/api/env';
+ *
+ * // for this example the 'index.html' file's `<base href ="/" />` tag is dynamically replaced during the build process to adapt to the deployment environment.
+ * const html = Deno.readTextFileSync(import.meta.dirname + '/dist/index.html')
+   .replace(
+     '<base href="/" />',
+     `<base href="${BASE_URL}" />`,
+   )
+ * ```
+ */
+export const BASE_URL: string = PROD('BASE_URL', '/')
+if (!BASE_URL.startsWith('/') || !BASE_URL.endsWith('/')) {
+  throw Error('incorrect BASE_URL: must start and end with /')
+}
+
 /**
  * TEST env getter
  *
diff --git a/api/server.ts b/api/server.ts
index 8110e19..78860a8 100644
--- a/api/server.ts
+++ b/api/server.ts
@@ -40,6 +40,7 @@ import { type RequestContext, runContext } from './context.ts'
 import { respond, ResponseError } from './response.ts'
 import { now } from '@01edu/time'
 import type { Awaitable } from '@01edu/types'
+import { BASE_URL } from './env.ts'
 
 type Handler = (ctx: RequestContext) => Awaitable<Response>
 /**
@@ -99,7 +100,7 @@ export const server = (
       setCookie(res.headers, {
         name: 'trace',
         value: String(ctx.trace),
-        path: '/',
+        path: BASE_URL,
         secure: true,
         httpOnly: true,
         sameSite: 'Lax',