diff --git a/README.md b/README.md
index 52f7c7f..f131cb7 100644
--- a/README.md
+++ b/README.md
@@ -2,12 +2,12 @@
 
 ## Routing rules
 - Static first routing
-- Path variables defined with `:foo`
+- Path variables defined with colon prefix: `:foo`
 - Example: `/odin/:version/download`
 - Wild card routing not implemented
 
 ## Compile time user errors included
-When defining the server you can pass a custom error type for the server. 
+When defining the server you can pass a custom error union type for the server. 
 All the handler function will, of course, need to return these in as a pair with a response.
 
 ## Memory allocation
@@ -27,6 +27,20 @@ import "core:strings"
 import fjord "fjord"
 import http "fjord/http"
 
+InternalError :: enum {
+    DatabaseError,
+}
+
+BadRequestError :: enum {
+    UserUnauthorised,
+    InputFormatWrong,
+}
+
+Error :: union {
+    InternalError,
+    BadRequestError,
+}
+
 // Handler for GET /hello/:name
 hello_handler :: proc(request: ^http.Request) -> (http.Response, Error) {
     name := request.path_variables["name"]
@@ -49,7 +63,7 @@ hello_handler :: proc(request: ^http.Request) -> (http.Response, Error) {
 // Handler for GET /users/:id/posts/:post_id
 user_post_handler :: proc(request: ^http.Request) -> (http.Response, Error) {
     user_id := request.path_variables["id"]
-    post_id := request.path_variables["post_id"]
+    post_id := request.path_variables["post-id"]
 
     body := strings.concatenate(
         {"<p>User ", user_id, " - Post ", post_id, "</p>"},
@@ -66,9 +80,32 @@ user_post_handler :: proc(request: ^http.Request) -> (http.Response, Error) {
     return response, nil
 }
 
-UserError :: enum {
-    DatabaseError,
-    ValidationError,
+error_callback :: proc(error: Error) -> http.Response {
+    switch err_type in error {
+        case BadRequestError:
+        switch err in err_type {
+            case UserUnauthorised: fallthrough
+            case InputFormatWrong:
+                body := "Bad request error"
+                return http.make_response(
+                    .BadRequest,
+                    transmute([]byte)body,
+                    .Html,
+                    context.temp_allocator,
+                )
+        }
+        case InternalError:
+        switch err in err_type {
+            case DataBaseError: 
+                body := "Internal server error"
+                return http.make_response(
+                    .InternalServerError,
+                    transmute([]byte)body,
+                    .Html,
+                    context.temp_allocator,
+                )
+        }
+    }
 }
 
 main :: proc() {
@@ -85,7 +122,9 @@ main :: proc() {
     defer fjord.server_destroy(&server)
 
     fjord.server_add_route(&server, .GET, {"hello", ":name"}, hello_handler)
-    fjord.server_add_route(&server, .GET, {"users", ":id", "posts", ":post_id"}, user_post_handler)
+    fjord.server_add_route(&server, .GET, {"users", ":id", "posts", ":post-id"}, user_post_handler)
+
+    server_set_error_handler(&server, error_callback)
 
     log.infof("Server listening on http://127.0.0.1:%d", endpoint.port)
     fjord.server_listen_and_serve(&server)