diff --git a/CHANGELOG.md b/CHANGELOG.md
index 86c4837..978ad14 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@
 - Added automatic role assignment for new OIDC users via `oidc.default_role` and IdP-provided role claims via `oidc.role_claim` (closes [#352](https://github.com/tale/headplane/issues/352)).
 - Fixed the DNS page crashing when Headscale has no Split DNS nameservers configured (closes [#570](https://github.com/tale/headplane/issues/570)).
 - User lists now show Headscale display names while preserving usernames as secondary text (closes [#571](https://github.com/tale/headplane/issues/571)).
+- Fixed the Register Machine Key dialog so it accepts registration URLs and full `hskey-authreq-...` registration keys (closes [#579](https://github.com/tale/headplane/issues/579)).
 
 ---
 
diff --git a/app/routes/machines/dialogs/new.tsx b/app/routes/machines/dialogs/new.tsx
index 523b723..41f4dc2 100644
--- a/app/routes/machines/dialogs/new.tsx
+++ b/app/routes/machines/dialogs/new.tsx
@@ -12,10 +12,11 @@ import Text from "~/components/text";
 import Title from "~/components/title";
 import { useForm } from "~/hooks/use-form";
 import type { User } from "~/types";
+import { normalizeRegistrationKey } from "~/utils/register-key";
 import { getUserDisplayName } from "~/utils/user";
 
 const registerSchema = type({
-  register_key: "string == 24",
+  register_key: "string > 0",
   user: "string > 0",
 });
 
@@ -28,7 +29,16 @@ export interface NewMachineProps {
 
 export default function NewMachine(data: NewMachineProps) {
   const [pushDialog, setPushDialog] = useState(false);
-  const form = useForm({ schema: registerSchema });
+  const form = useForm({
+    schema: registerSchema,
+    validate: (values) =>
+      normalizeRegistrationKey(String(values.register_key ?? ""))
+        ? undefined
+        : {
+            register_key:
+              "Paste the registration URL or full hskey-authreq-... key from tailscale up.",
+          },
+  });
   const navigate = useNavigate();
 
   return (
@@ -43,7 +53,8 @@ export default function NewMachine(data: NewMachineProps) {
             {...form.field("register_key")}
             required
             label="Machine Key"
-            placeholder="AbCd..."
+            placeholder="hskey-authreq-XXXXXXXXXXXXXXXXXXXXXXXX"
+            description="Paste the registration URL or full key shown by tailscale up."
           />
           <Select
             required
diff --git a/app/routes/machines/machine-actions.ts b/app/routes/machines/machine-actions.ts
index 8d15ff2..fbb0a85 100644
--- a/app/routes/machines/machine-actions.ts
+++ b/app/routes/machines/machine-actions.ts
@@ -4,6 +4,7 @@ import { authContext, headscaleLiveStoreContext, requestApiContext } from "~/ser
 import { isDataWithApiError } from "~/server/headscale/api/error-client";
 import { nodesResource } from "~/server/headscale/live-store";
 import { Capabilities } from "~/server/web/roles";
+import { normalizeRegistrationKey } from "~/utils/register-key";
 
 import type { Route } from "./+types/machine";
 
@@ -31,13 +32,20 @@ export async function machineAction({ request, context }: Route.ActionArgs) {
       });
     }
 
-    const registrationKey = formData.get("register_key")?.toString();
-    if (!registrationKey) {
+    const registrationKeyInput = formData.get("register_key")?.toString();
+    if (!registrationKeyInput) {
       throw data("Missing `register_key` in the form data.", {
         status: 400,
       });
     }
 
+    const registrationKey = normalizeRegistrationKey(registrationKeyInput);
+    if (!registrationKey) {
+      throw data("Invalid `register_key` in the form data.", {
+        status: 400,
+      });
+    }
+
     const user = formData.get("user")?.toString();
     if (!user) {
       throw data("Missing `user` in the form data.", {
diff --git a/app/server/headscale/api/capabilities.ts b/app/server/headscale/api/capabilities.ts
index 212ab0e..b3e9846 100644
--- a/app/server/headscale/api/capabilities.ts
+++ b/app/server/headscale/api/capabilities.ts
@@ -36,6 +36,14 @@ export interface Capabilities {
    * 0.28.0+.
    */
   readonly nodeOwnerIsImmutable: boolean;
+
+  /**
+   * The `POST /api/v1/node/register` endpoint expects the full
+   * `hskey-authreq-<id>` AuthID as the `key` parameter. Pre-0.29
+   * Headscale expected the raw 24-character registration ID without
+   * the `hskey-authreq-` prefix. Introduced in 0.29.0.
+   */
+  readonly registerKeyIncludesAuthReqPrefix: boolean;
 }
 
 export function capabilitiesFor(version: ServerVersion): Capabilities {
@@ -43,5 +51,6 @@ export function capabilitiesFor(version: ServerVersion): Capabilities {
     preAuthKeysHaveStableIds: gte(version, "0.28.0"),
     nodeTagsAreFlat: gte(version, "0.28.0"),
     nodeOwnerIsImmutable: gte(version, "0.28.0"),
+    registerKeyIncludesAuthReqPrefix: gte(version, "0.29.0"),
   };
 }
diff --git a/app/server/headscale/api/resources/nodes.ts b/app/server/headscale/api/resources/nodes.ts
index fb0d487..6fef30a 100644
--- a/app/server/headscale/api/resources/nodes.ts
+++ b/app/server/headscale/api/resources/nodes.ts
@@ -62,14 +62,19 @@ export function makeNodeApi(
     register: async (user, key) => {
       // Headscale's node-register endpoint expects the registration
       // params as both query string and body — preserved as-is.
+      // Pre-0.29 expects the raw 24-char registration ID; 0.29+ expects
+      // the full `hskey-authreq-<id>` AuthID.
+      const registerKey = capabilities.registerKeyIncludesAuthReqPrefix
+        ? key
+        : key.replace(/^hskey-authreq-/, "");
       const qp = new URLSearchParams();
       qp.append("user", user);
-      qp.append("key", key);
+      qp.append("key", registerKey);
       const { node } = await transport.request<{ node: RawMachine }>({
         method: "POST",
         path: `v1/node/register?${qp.toString()}`,
         apiKey,
-        body: { user, key },
+        body: { user, key: registerKey },
       });
       return normalize(node);
     },
diff --git a/app/utils/register-key.ts b/app/utils/register-key.ts
new file mode 100644
index 0000000..4b9a1f2
--- /dev/null
+++ b/app/utils/register-key.ts
@@ -0,0 +1,46 @@
+const authRequestKeyPattern = /^hskey-authreq-[A-Za-z0-9_-]{16,}$/;
+const authRequestKeySearchPattern = /hskey-authreq-[A-Za-z0-9_-]{16,}/;
+const legacyMachineKeyPattern = /^mkey:[A-Za-z0-9_-]{16,}$/;
+const registerUrlPattern = /\/register\/([^\s?#]+)/;
+const registrationKeySuffixPattern = /^[A-Za-z0-9_-]{24,}$/;
+
+export function normalizeRegistrationKey(value: string): string | null {
+  const trimmed = value.trim();
+  if (trimmed.length === 0) {
+    return null;
+  }
+
+  const registerUrlMatch = trimmed.match(registerUrlPattern);
+  if (registerUrlMatch) {
+    const token = normalizeRegistrationToken(registerUrlMatch[1]);
+    if (token) {
+      return token;
+    }
+  }
+
+  const authRequestKeyMatch = trimmed.match(authRequestKeySearchPattern);
+  if (authRequestKeyMatch) {
+    return authRequestKeyMatch[0];
+  }
+
+  return normalizeRegistrationToken(trimmed);
+}
+
+function normalizeRegistrationToken(value: string): string | null {
+  let token: string;
+  try {
+    token = decodeURIComponent(value.trim());
+  } catch {
+    return null;
+  }
+
+  if (authRequestKeyPattern.test(token) || legacyMachineKeyPattern.test(token)) {
+    return token;
+  }
+
+  if (registrationKeySuffixPattern.test(token)) {
+    return `hskey-authreq-${token}`;
+  }
+
+  return null;
+}
diff --git a/tests/integration/api/nodes.test.ts b/tests/integration/api/nodes.test.ts
index 91105e2..27b4a3e 100644
--- a/tests/integration/api/nodes.test.ts
+++ b/tests/integration/api/nodes.test.ts
@@ -1,19 +1,63 @@
-import { describe, expect, test } from "vitest";
+import { RouterContextProvider } from "react-router";
+import { describe, expect, test, vi } from "vitest";
+
+import { machineAction } from "~/routes/machines/machine-actions";
+import { authContext, headscaleLiveStoreContext, requestApiContext } from "~/server/context";
+import { Capabilities } from "~/server/web/roles";
 
 import { getBootstrapClient, getNode, getRuntimeClient, HS_VERSIONS } from "../setup/env";
 
+function registerRequest(registerKey: string) {
+  const form = new FormData();
+  form.set("action_id", "register");
+  form.set("register_key", registerKey);
+  form.set("user", "node-reg@");
+
+  return new Request("http://headplane.test/machines", {
+    method: "POST",
+    body: form,
+  });
+}
+
+function actionContext(api: Awaited<ReturnType<typeof getRuntimeClient>>) {
+  const auth = { can: vi.fn(() => true) };
+  const liveStore = { refresh: vi.fn() };
+  const principal = { id: "integration-user" };
+  const context = new RouterContextProvider();
+
+  context.set(authContext, auth as never);
+  context.set(headscaleLiveStoreContext, liveStore as never);
+  context.set(requestApiContext, vi.fn(async () => ({ principal, api })) as never);
+
+  return { auth, context, liveStore };
+}
+
 describe.sequential.for(HS_VERSIONS)("Headscale %s: Users", (version) => {
   let workingNodeId: string;
 
-  test("nodes can register via their nodekey", async () => {
+  test("nodes can register from a Tailscale registration URL", async () => {
     const client = await getRuntimeClient(version);
     const tailnetNode = await getNode(version);
+    const { auth, context, liveStore } = actionContext(client);
 
     const user = await client.users.create({ name: "node-reg@" });
-    const node = await client.nodes.register(user.name, tailnetNode.authCode);
+    expect(user.name).toBe("node-reg@");
+
+    const response = await machineAction({
+      request: registerRequest(tailnetNode.registerUrl),
+      context,
+      params: {},
+    } as never);
+
+    expect(auth.can).toHaveBeenCalledWith(expect.anything(), Capabilities.write_machines);
+    expect(liveStore.refresh).toHaveBeenCalledOnce();
+    expect(response).toBeInstanceOf(Response);
+    expect((response as Response).status).toBe(302);
+
+    const nodes = await client.nodes.list();
+    const node = nodes.find((n) => n.name === tailnetNode.nodeName);
     expect(node).toBeDefined();
-    expect(node.registerMethod).toBe("REGISTER_METHOD_CLI");
-    expect(node.name).toBe(tailnetNode.nodeName);
+    expect(node?.registerMethod).toBe("REGISTER_METHOD_CLI");
   });
 
   test("nodes can be retrieved", async () => {
diff --git a/tests/integration/setup/env.ts b/tests/integration/setup/env.ts
index 26554ad..661babe 100644
--- a/tests/integration/setup/env.ts
+++ b/tests/integration/setup/env.ts
@@ -44,6 +44,7 @@ export async function getNode(version: Version) {
   const { tailscaleNode } = await ensureVersion(version);
   return {
     authCode: tailscaleNode.authCode,
+    registerUrl: tailscaleNode.registerUrl,
     nodeName: tailscaleNode.nodeName,
   };
 }
diff --git a/tests/integration/setup/start-tailscale.ts b/tests/integration/setup/start-tailscale.ts
index ca8952e..b53c7da 100644
--- a/tests/integration/setup/start-tailscale.ts
+++ b/tests/integration/setup/start-tailscale.ts
@@ -9,6 +9,7 @@ export type Version = string;
 export interface TailscaleNodeEnv {
   container: tc.StartedTestContainer;
   authCode: string;
+  registerUrl: string;
   nodeName: string;
 }
 
@@ -53,7 +54,7 @@ export async function startTailscaleNode(
         if (!token) return;
 
         authCodeResolved = true;
-        resolveAuthCode(token);
+        resolveAuthCode(`${prefix}${token}`);
         rl.close();
       });
 
@@ -68,7 +69,7 @@ export async function startTailscaleNode(
     .withWaitStrategy(tc.Wait.forLogMessage(prefix).withStartupTimeout(30_000))
     .start();
 
-  const authCode = await Promise.race<string>([
+  const registerUrl = await Promise.race<string>([
     authCodePromise,
     new Promise((_, reject) =>
       setTimeout(
@@ -77,6 +78,7 @@ export async function startTailscaleNode(
       ),
     ),
   ]);
+  const authCode = registerUrl.slice(prefix.length);
 
-  return { container, authCode, nodeName };
+  return { container, authCode, registerUrl, nodeName };
 }
diff --git a/tests/unit/headscale/server-version.test.ts b/tests/unit/headscale/server-version.test.ts
index dd158bf..399a0db 100644
--- a/tests/unit/headscale/server-version.test.ts
+++ b/tests/unit/headscale/server-version.test.ts
@@ -82,6 +82,7 @@ describe("capabilitiesFor", () => {
       preAuthKeysHaveStableIds: true,
       nodeTagsAreFlat: true,
       nodeOwnerIsImmutable: true,
+      registerKeyIncludesAuthReqPrefix: false,
     });
   });
 
@@ -91,10 +92,16 @@ describe("capabilitiesFor", () => {
     );
   });
 
+  test("0.29.0 enables the prefixed AuthID register key", () => {
+    const caps = capabilitiesFor(parseServerVersion("0.29.0"));
+    expect(caps.registerKeyIncludesAuthReqPrefix).toBe(true);
+  });
+
   test("0.27.1 lacks every 0.28-gated capability", () => {
     const caps = capabilitiesFor(parseServerVersion("0.27.1"));
     expect(caps.preAuthKeysHaveStableIds).toBe(false);
     expect(caps.nodeTagsAreFlat).toBe(false);
     expect(caps.nodeOwnerIsImmutable).toBe(false);
+    expect(caps.registerKeyIncludesAuthReqPrefix).toBe(false);
   });
 });
diff --git a/tests/unit/utils/register-key.test.ts b/tests/unit/utils/register-key.test.ts
new file mode 100644
index 0000000..5720c74
--- /dev/null
+++ b/tests/unit/utils/register-key.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, test } from "vitest";
+
+import { normalizeRegistrationKey } from "~/utils/register-key";
+
+const suffix = "ABCDEFGHIJKLMNOPQRSTUVWX";
+const key = `hskey-authreq-${suffix}`;
+const legacyKey = "mkey:0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+describe("normalizeRegistrationKey", () => {
+  test("keeps full registration keys", () => {
+    expect(normalizeRegistrationKey(key)).toBe(key);
+  });
+
+  test("keeps legacy machine keys", () => {
+    expect(normalizeRegistrationKey(legacyKey)).toBe(legacyKey);
+  });
+
+  test("trims surrounding whitespace", () => {
+    expect(normalizeRegistrationKey(`  ${key}\n`)).toBe(key);
+  });
+
+  test("extracts keys from registration URLs", () => {
+    expect(normalizeRegistrationKey(`https://headscale.example.com/register/${key}`)).toBe(key);
+  });
+
+  test("extracts legacy machine keys from registration URLs", () => {
+    expect(normalizeRegistrationKey(`https://headscale.example.com/register/${legacyKey}`)).toBe(
+      legacyKey,
+    );
+  });
+
+  test("extracts keys from registration URLs with trailing URL parts", () => {
+    expect(normalizeRegistrationKey(`https://headscale.example.com/register/${key}?foo=bar`)).toBe(
+      key,
+    );
+  });
+
+  test("extracts auth request keys from URLs with trailing punctuation", () => {
+    expect(normalizeRegistrationKey(`https://headscale.example.com/register/${key}.`)).toBe(key);
+  });
+
+  test("accepts suffix-only input as a fallback", () => {
+    expect(normalizeRegistrationKey(suffix)).toBe(key);
+  });
+
+  test("does not require an exact suffix length for full keys", () => {
+    const longerKey = `${key}YZ12`;
+    expect(normalizeRegistrationKey(longerKey)).toBe(longerKey);
+  });
+
+  test("rejects empty or unrelated input", () => {
+    expect(normalizeRegistrationKey("   ")).toBeNull();
+    expect(normalizeRegistrationKey("not-a-registration-key")).toBeNull();
+    expect(normalizeRegistrationKey("hskey-authreq-short")).toBeNull();
+    expect(normalizeRegistrationKey("https://headscale.example.com/register/not-a-key")).toBeNull();
+  });
+});