diff --git a/README.md b/README.md
index b57c702..fc4eced 100644
--- a/README.md
+++ b/README.md
@@ -9,9 +9,11 @@ GitHub Action for creating a GitHub App installation access token.
 In order to use this action, you need to:
 
 1. [Register new GitHub App](https://docs.github.com/apps/creating-github-apps/setting-up-a-github-app/creating-a-github-app).
-2. [Store the App's ID or Client ID in your repository environment variables](https://docs.github.com/actions/learn-github-actions/variables#defining-configuration-variables-for-multiple-workflows) (example: `APP_ID`).
+2. [Store the App's Client ID (recommended) or App ID in your repository environment variables](https://docs.github.com/actions/learn-github-actions/variables#defining-configuration-variables-for-multiple-workflows) (example: `APP_ID`).
 3. [Store the App's private key in your repository secrets](https://docs.github.com/actions/security-guides/encrypted-secrets?tool=webui#creating-encrypted-secrets-for-a-repository) (example: `PRIVATE_KEY`).
 
+Pass the App's Client ID or App ID using the `app-id` input. GitHub recommends using the Client ID when available.
+
 > [!IMPORTANT]  
 > An installation access token expires after 1 hour. Please [see this comment](https://github.com/actions/create-github-app-token/issues/121#issuecomment-2043214796) for alternative approaches if you have long-running processes.
 
@@ -318,7 +320,7 @@ If you set `HTTP_PROXY` or `HTTPS_PROXY`, also set `NODE_USE_ENV_PROXY: "1"` on
 
 ### `app-id`
 
-**Required:** GitHub App ID.
+**Required:** GitHub App Client ID or App ID. GitHub recommends using the Client ID when available.
 
 ### `private-key`
 
diff --git a/action.yml b/action.yml
index ba4e915..e614e7e 100644
--- a/action.yml
+++ b/action.yml
@@ -6,7 +6,7 @@ branding:
   color: "gray-dark"
 inputs:
   app-id:
-    description: "GitHub App ID"
+    description: "GitHub App ID or Client ID"
     required: true
   private-key:
     description: "GitHub App private key"
diff --git a/tests/index.js.snapshot b/tests/index.js.snapshot
index 06cac80..e230cee 100644
--- a/tests/index.js.snapshot
+++ b/tests/index.js.snapshot
@@ -1,3 +1,20 @@
+exports[`main-client-id.test.js > stdout 1`] = `
+Inputs 'owner' and 'repositories' are not set. Creating token for this repository (actions/create-github-app-token).
+::add-mask::ghs_16C7e42F292c6912E7710c838347Ae178B4a
+
+::set-output name=token::ghs_16C7e42F292c6912E7710c838347Ae178B4a
+
+::set-output name=installation-id::123456
+
+::set-output name=app-slug::github-actions
+::save-state name=token::ghs_16C7e42F292c6912E7710c838347Ae178B4a
+::save-state name=expiresAt::2016-07-11T22:14:10Z
+--- REQUESTS ---
+GET /repos/actions/create-github-app-token/installation
+POST /app/installations/123456/access_tokens
+{"repositories":["create-github-app-token"]}
+`;
+
 exports[`main-custom-github-api-url.test.js > stdout 1`] = `
 Inputs 'owner' and 'repositories' are set. Creating token for the following repositories:
       
diff --git a/tests/main-client-id.test.js b/tests/main-client-id.test.js
new file mode 100644
index 0000000..7af6c91
--- /dev/null
+++ b/tests/main-client-id.test.js
@@ -0,0 +1,6 @@
+import { test } from "./main.js";
+
+// Verify `main` accepts a GitHub App client ID via the `app-id` input
+await test(() => {
+  process.env["INPUT_APP-ID"] = "Iv1.0123456789abcdef";
+});