diff --git a/backend/README.md b/backend/README.md
index 0989c15..01e41da 100644
--- a/backend/README.md
+++ b/backend/README.md
@@ -60,7 +60,13 @@ See [spec](spec) for more details
 
 ## API Routes
 
-All routes are NIP-98 protected.
+Most API routes are NIP-98 protected.
+
+Public exceptions:
+
+- `GET /plans`
+- `GET /plans/:id`
+- `POST /stripe/webhook` (validated with Stripe signatures instead)
 
 - `GET /identity` — get auth identity (`pubkey`, `is_admin`)
 - `GET /tenants` — list tenants (admin)
@@ -73,3 +79,13 @@ All routes are NIP-98 protected.
 - `PUT /relays/:id` — update relay (admin or relay tenant)
 - `POST /relays/:id/deactivate` — deactivate relay (admin or relay tenant)
 - `GET /invoices` — list invoices (`?tenant=<pubkey>` allowed for admin only)
+
+## API Auth Model
+
+Caravel intentionally uses a session-style variant of NIP-98 for client-to-backend API auth.
+
+- Frontend signs one kind `27235` event with `u = VITE_API_URL` and caches that header for about 10 minutes.
+- Backend verifies event kind, signature, and that `u` contains configured `HOST`.
+- Backend intentionally does not bind auth to exact request URL/method/query, and does not enforce payload hash, timestamp freshness window, or replay cache.
+- Goal: reduce repeated wallet signing prompts and avoid cookie-based sessions.
+- Tradeoff: this is weaker request-intent binding than strict NIP-98 semantics.
diff --git a/backend/spec/api.md b/backend/spec/api.md
index 831efd9..872d0a2 100644
--- a/backend/spec/api.md
+++ b/backend/spec/api.md
@@ -184,9 +184,11 @@ Notes:
 ## `extract_auth_pubkey(&self, headers: &HeaderMap) -> Result<String>`
 
 - Parses `Authorization` header
-- Validates event kind and signature using `nostr_sdk`
-- Validates event `u` against `HOST` (not the request path. Non-standard, but correct)
-- Does not validate `method` tag
+- Validates event kind (`27235`) and signature using `nostr_sdk`
+- Validates event `u` contains configured `HOST`
+- Intentionally does **not** enforce exact request URL/method/query matching
+- Intentionally does **not** validate `payload` tag/hash, `created_at` freshness window, or replay nonce/cache
+- This is a deliberate session-style tradeoff to reduce repeated signer prompts in the client
 - Returns pubkey if header all checks pass
 
 Refer to https://github.com/nostr-protocol/nips/blob/master/98.md for details. Use `nostr_sdk` functionality where possible.
diff --git a/backend/src/api.rs b/backend/src/api.rs
index 6f68808..ec98a46 100644
--- a/backend/src/api.rs
+++ b/backend/src/api.rs
@@ -209,6 +209,9 @@ impl Api {
             return Err(ApiError::Unauthorized(anyhow!("missing u tag")));
         };
 
+        // Intentional session-style variant of NIP-98 for Caravel API auth.
+        // We validate signer identity plus host affinity, and do not bind to exact
+        // request URL/method or maintain replay state here.
         if !self.host.is_empty() && !got_u.contains(&self.host) {
             return Err(ApiError::Unauthorized(anyhow!(
                 "authorization host mismatch"
diff --git a/frontend/README.md b/frontend/README.md
index f4802ee..5d2d67c 100644
--- a/frontend/README.md
+++ b/frontend/README.md
@@ -51,8 +51,11 @@ npm run preview
 
 ## Authentication
 
-- Tenant requests use NIP-98 tokens derived from the logged-in user
-- Admin routes require a pubkey listed in `PLATFORM_ADMIN_PUBKEYS` on the backend
+- Tenant requests use an intentional session-style variant of NIP-98:
+  - The client signs one kind `27235` event with `u = VITE_API_URL`.
+  - The resulting `Authorization` header is cached for about 10 minutes to avoid repeated signer prompts.
+  - The backend validates signer identity + host affinity rather than exact URL/method binding per request.
+- Admin routes require a pubkey listed in `ADMINS` on the backend.
 
 ## Routes
 
diff --git a/frontend/src/lib/api.ts b/frontend/src/lib/api.ts
index 6d26250..4c23b6c 100644
--- a/frontend/src/lib/api.ts
+++ b/frontend/src/lib/api.ts
@@ -145,6 +145,8 @@ export async function makeAuth(): Promise<string | undefined> {
     kind: 27235,
     content: "",
     created_at: Math.floor(now / 1000),
+    // Intentional session-style auth: sign the API base URL once, then reuse
+    // the header briefly to avoid prompting the signer on every request.
     tags: [["u", API_URL]],
   })