diff --git a/apps/docs/architecture/overview.md b/apps/docs/architecture/overview.md
new file mode 100644
index 0000000..308e6aa
--- /dev/null
+++ b/apps/docs/architecture/overview.md
@@ -0,0 +1,54 @@
+---
+title: Architecture Overview
+description: How TRAWL's components fit together — embedded browser pool, session cache, and tiered execution.
+---
+
+# Architecture Overview
+
+```
+Client (Prowlarr, curl, your code)
+           │
+           ▼
+      Elysia API (apps/api)
+    ┌──────────────────────────┐
+    │  POST /v1   POST /scrape │
+    │  GET /health  GET /stats │
+    └────────────┬─────────────┘
+                 │ direct call
+                 ▼
+      Orchestrator (packages/tiers)
+    ┌──────────────────────────────────────┐
+    │    ├── Tier 1: plain Bun fetch       │
+    │    ├── Tier 2: cached session + pool │
+    │    ├── Tier 3: fresh solve + pool    │
+    │    └── Tier 4: residential proxy     │
+    └──────────────┬───────────────────────┘
+          ┌────────┴──────────┐
+          ▼                   ▼
+   BrowserPool          SessionCache
+   (packages/browser)   (packages/browser)
+          │                   │
+          ▼                   ▼
+     Camoufox            Redis (cache)
+     Firefox N×
+```
+
+## Components
+
+### API (`apps/api`)
+
+An Elysia HTTP server. Accepts scrape requests and calls the orchestrator inline — all browser work happens in the same process. Exposes `/health` and `/stats` for monitoring.
+
+### Browser Pool (`packages/browser/src/pool.ts`)
+
+Maintains a fixed set of `{ browser, context }` pairs using [Camoufox](https://github.com/daijro/camoufox) (Firefox with fingerprint patching at the C++/Juggler level). Acquisition is sticky — if a browser last served `example.com`, it is preferred for the next request to `example.com`. Browsers accumulate domain cookies across requests, which makes subsequent challenges faster.
+
+### Session Cache (`packages/browser/src/session.ts`)
+
+Stores `{ cookies, userAgent, savedAt }` in Redis, keyed by hostname (`session:example.com`). The TTL is configurable (default 1 hour). Tier 3 writes to it on every successful challenge solve. Tier 2 reads from it at the start of every request.
+
+Redis is optional — if `REDIS_URL` is not set, the session cache is disabled and every request escalates to Tier 3.
+
+### Tiers (`packages/tiers`)
+
+The escalation logic. See [Tiered Execution](/architecture/tiered-execution) for the full breakdown.