diff --git a/src/constants.ts b/src/constants.ts
index d8d0556..3c32857 100644
--- a/src/constants.ts
+++ b/src/constants.ts
@@ -29,3 +29,5 @@ export const HITCHMAPS_AUTHOR_PUBLIC_KEY =
   "53055ee011e96a00a705b38253b9cbc6614ccbd37df4dad42ec69bbe608c4209" as const;
 
 export const TRUSTROOTS_NPUB_PUT_URL = "https://www.trustroots.org/api/users";
+export const TRUSTROOTS_NIP5_URL =
+  "https://www.trustroots.org/.well-known/nostr.json";
diff --git a/src/nostr/nip5.ts b/src/nostr/nip5.ts
new file mode 100644
index 0000000..e40bb78
--- /dev/null
+++ b/src/nostr/nip5.ts
@@ -0,0 +1,32 @@
+import { TRUSTROOTS_NIP5_URL } from "../constants";
+import { getTrustrootsUsernameFromLocation } from "../router";
+import { alert } from "../utils";
+import { getPublicKey } from "./keys";
+
+export const validateNip5 = async () => {
+  try {
+    const username = getTrustrootsUsernameFromLocation();
+    if (username.length < 3) {
+      alert(
+        `Sorry, you need to click to this page from trustroots.org. Without doing that, this site won't work properly. Please go to www.trustroots.org and click the Notes link to come back here. #wBjsEe`,
+        `You need to click from trustroots`
+      );
+      return;
+    }
+
+    const result = await fetch(`${TRUSTROOTS_NIP5_URL}?name=${username}`);
+    const nip5 = (await result.json()) as {
+      names: { [username: string]: string };
+    };
+    const nip5PublicKey = nip5.names?.[username];
+    const localPublicKey = await getPublicKey();
+    if (nip5PublicKey !== localPublicKey) {
+      alert(
+        `Your key doesn't match trustroots. Posting to the map will not work. Please sign out and sign in again with the nsec key that matches your trustroots npub key. #H9bEe2`,
+        "Fatal error"
+      );
+    }
+  } catch (error) {
+    alert(error, `Unexpected error`);
+  }
+};
diff --git a/src/startup.ts b/src/startup.ts
index 024c85d..e5d8d5c 100644
--- a/src/startup.ts
+++ b/src/startup.ts
@@ -12,6 +12,7 @@ import {
 import { getDefaultRelays } from "./nostr/relays";
 import { startUserOnboarding } from "./onboarding";
 import { startWelcomeSequence } from "./welcome";
+import { validateNip5 } from "./nostr/nip5";
 
 export const startup = async () => {
   const isLoggedIn = await hasPrivateKey();
@@ -31,6 +32,8 @@ export const startup = async () => {
   const loggedOut = L.DomUtil.get("loggedOut")!;
 
   if (isLoggedIn) {
+    validateNip5();
+
     L.DomUtil.addClass(loggedIn, "show");
     L.DomUtil.addClass(loggedOut, "hide");
 
diff --git a/src/utils.ts b/src/utils.ts
index f80c434..fb98a7f 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -16,8 +16,9 @@ export const confirmYesNo = async (text: string) => {
   return false;
 };
 
-export const alert = async (text: string) => {
+export const alert = async (text: string, title?: string) => {
   await Swal.fire({
+    title,
     text,
   });
 };