diff --git a/README.md b/README.md
index b4a0f56..a60e787 100644
--- a/README.md
+++ b/README.md
@@ -14,9 +14,89 @@ The library intentionally does not know anything about snapshots, route
 progress, geolocation, frontend state, or media playback rules. It only parses,
 validates, stores, logs, and returns BVK content state.
 
+## Install
+
+```bash
+go get gitea.unprism.ru/KRBL/mila
+```
+
+## Scope
+
+Mila is a protocol library. It should be embedded into an application service,
+for example `wn-content`, and exposed on the address required by the transport
+integration.
+
+Mila does:
+
+- parse `GET /set-content`
+- parse `GET /get-content`
+- validate `route`, `str`, and `tpl_name`
+- URL-decode query parameters through Go's standard HTTP parser
+- store the latest state in memory or in a JSON file
+- return protocol-compatible JSON
+- log each HTTP request with method, path, status, remote address, and duration
+- call an optional callback after successful `set-content`
+
+Mila does not:
+
+- calculate route progress
+- work with geolocation or NMEA
+- map `tpl_name` to real media playlists
+- read or write snapshots
+- communicate with frontend directly
+- decide how content should be rendered
+
+## Protocol
+
+The media complex acts as an HTTP server. BVK acts as an HTTP client.
+
+Default address from the PDF:
+
+```text
+172.16.16.2:13280
+```
+
+Endpoints:
+
+```text
+GET /set-content?route=<R>&str=<S>&tpl_name=<T>
+GET /get-content
+```
+
+`set-content` accepts URL-encoded query parameters:
+
+| Parameter | Required | Meaning |
+| --- | --- | --- |
+| `route` | yes | route number, default limit is 1-3 characters |
+| `str` | no | ticker/running text, default limit is 200 characters |
+| `tpl_name` | yes | media content template name, default limit is 200 characters |
+
+`get-content` response:
+
+```json
+{
+  "route": "3",
+  "str": "Гостиный двор - Gostiny dvor",
+  "tpl_name": "Гостиный двор"
+}
+```
+
+`updated_at` is stored internally but is not exposed by `/get-content`, because
+the protocol response should stay strict.
+
 ## Usage
 
 ```go
+package main
+
+import (
+    "log"
+    "net/http"
+
+    "gitea.unprism.ru/KRBL/mila"
+)
+
+func main() {
 store := mila.NewFileStore("/srv/persistence/client_logs/bvk_content.json")
 
 handler := mila.NewHandler(mila.DefaultConfig(), store,
@@ -29,9 +109,68 @@ srv := &http.Server{
     Addr:    "0.0.0.0:13280",
     Handler: handler,
 }
+
+log.Fatal(srv.ListenAndServe())
+}
 ```
 
-## State
+## Configuration
+
+Default validation config:
+
+```go
+cfg := mila.DefaultConfig()
+```
+
+Which currently means:
+
+```go
+mila.Config{
+    MaxRouteLen:    3,
+    MaxTextLen:     200,
+    MaxTemplateLen: 200,
+}
+```
+
+The text/template limits should be confirmed with the integrator. The provided
+PDF has an ambiguous text layer for those values.
+
+## Stores
+
+Use `MemoryStore` when state does not need to survive process restart:
+
+```go
+store := mila.NewMemoryStore()
+```
+
+Use `FileStore` on a device when the latest BVK state should be persisted:
+
+```go
+store := mila.NewFileStore("/srv/persistence/client_logs/bvk_content.json")
+```
+
+`FileStore` writes atomically through a temporary file and keeps an in-memory
+copy after the first successful read or write.
+
+## Callback
+
+`WithOnSet` lets the host application react to a valid BVK update:
+
+```go
+handler := mila.NewHandler(mila.DefaultConfig(), store,
+    mila.WithOnSet(func(state mila.ContentState) {
+        // Example host-side decisions:
+        // - publish route and ticker to frontend state
+        // - map state.Template to a local playlist/template
+        // - write application-specific logs
+    }),
+)
+```
+
+The callback is intentionally synchronous. Keep it fast; if integration work is
+heavy, push the state into an internal queue.
+
+## State Model
 
 ```json
 {
@@ -41,3 +180,48 @@ srv := &http.Server{
   "updated_at": "2026-07-12T12:00:00Z"
 }
 ```
+
+Go type:
+
+```go
+type ContentState struct {
+    Route     string    `json:"route"`
+    Text      string    `json:"str"`
+    Template  string    `json:"tpl_name"`
+    UpdatedAt time.Time `json:"updated_at,omitempty"`
+}
+```
+
+## Status Codes
+
+| Code | When |
+| ---: | --- |
+| 200 | valid `set-content` or ready `get-content` |
+| 400 | invalid request parameters |
+| 404 | unknown path |
+| 405 | method is not `GET` |
+| 500 | store/internal error |
+| 503 | `get-content` before first state, canceled/deadline context, unavailable dependency |
+
+Error response:
+
+```json
+{
+  "error": "route: must be at most 3 characters"
+}
+```
+
+## Testing
+
+```bash
+go test ./...
+```
+
+Current tests cover:
+
+- successful `set-content` + `get-content`
+- `get-content` before state is ready
+- invalid route validation
+- UTF-8 text/template validation
+- file store persistence
+- missing file store state
diff --git a/store_file_test.go b/store_file_test.go
new file mode 100644
index 0000000..9446756
--- /dev/null
+++ b/store_file_test.go
@@ -0,0 +1,47 @@
+package mila
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+)
+
+func TestFileStorePersistsAndLoadsState(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "bvk_content.json")
+	ctx := context.Background()
+
+	first := NewFileStore(path)
+	state := ContentState{
+		Route:    "3",
+		Text:     "Гостиный двор",
+		Template: "main",
+	}
+	if err := first.Set(ctx, state); err != nil {
+		t.Fatalf("set state: %v", err)
+	}
+
+	second := NewFileStore(path)
+	got, err := second.Get(ctx)
+	if err != nil {
+		t.Fatalf("get state: %v", err)
+	}
+
+	if got.Route != state.Route || got.Text != state.Text || got.Template != state.Template {
+		t.Fatalf("unexpected state: %+v", got)
+	}
+	if got.UpdatedAt.IsZero() != state.UpdatedAt.IsZero() {
+		t.Fatalf("unexpected updated_at value: %s", got.UpdatedAt)
+	}
+}
+
+func TestFileStoreMissingFileReturnsNotReady(t *testing.T) {
+	store := NewFileStore(filepath.Join(t.TempDir(), "missing.json"))
+
+	_, err := store.Get(context.Background())
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	if err != ErrNotReady {
+		t.Fatalf("expected ErrNotReady, got %v", err)
+	}
+}