diff --git a/action.yml b/action.yml
index 94a8dc4..434ddcb 100644
--- a/action.yml
+++ b/action.yml
@@ -38,3 +38,10 @@ outputs:
           https://sdk.ably.com/builds/ably/ably-flutter/pull/307/dartdoc/
 
       When used in the Flutter SDK repository, with `artifactName` as `"dartdoc"`.
+  base-path:
+    description: |
+      The base path. For example:
+
+          /builds/ably/ably-flutter/pull/307/dartdoc/
+
+      Useful when needing to know the relative path.
diff --git a/src/index.ts b/src/index.ts
index adf0b2a..c15972c 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -96,6 +96,8 @@ core.debug(`GitHub Environment Name: ${githubEnvironmentName}`);
 
 const urlBase = `https://${s3BucketName}/${s3KeyPrefix}/`;
 core.setOutput('url-base', urlBase);
+core.setOutput('base-path', s3KeyPrefix);
+
 const runMode = core.getInput('mode');
 if (runMode === 'preempt') {
   process.exit(0);