diff --git a/src/main/java/org/jenkinsci/plugins/github_branch_source/GitHubRepoSizeEstimator.java b/src/main/java/org/jenkinsci/plugins/github_branch_source/GitHubRepoSizeEstimator.java
new file mode 100644
index 000000000..68cda612f
--- /dev/null
+++ b/src/main/java/org/jenkinsci/plugins/github_branch_source/GitHubRepoSizeEstimator.java
@@ -0,0 +1,44 @@
+package org.jenkinsci.plugins.github_branch_source;
+
+import com.cloudbees.plugins.credentials.common.StandardCredentials;
+import hudson.Extension;
+import hudson.model.Item;
+import jenkins.plugins.git.GitToolChooser;
+import org.kohsuke.github.GHRepository;
+import org.kohsuke.github.GitHub;
+
+public class GitHubRepoSizeEstimator {
+  /**
+   * This extension intends to perform a GET request without any credentials on the provided
+   * repository URL to return the size of repository.
+   */
+  @Extension
+  public static class RepositorySizeGithubAPI extends GitToolChooser.RepositorySizeAPI {
+
+    @Override
+    public boolean isApplicableTo(String repoUrl, Item context, String credentialsId) {
+      StandardCredentials credentials =
+          Connector.lookupScanCredentials(context, repoUrl, credentialsId);
+      try {
+        GitHubRepositoryInfo info = GitHubRepositoryInfo.forRepositoryUrl(repoUrl);
+        GitHub gitHub = Connector.connect(info.getApiUri(), credentials);
+        gitHub.checkApiUrlValidity();
+      } catch (Exception e) {
+        return false;
+      }
+      return true;
+    }
+
+    @Override
+    public Long getSizeOfRepository(String repoUrl, Item context, String credentialsId)
+        throws Exception {
+      StandardCredentials credentials =
+          Connector.lookupScanCredentials(context, repoUrl, credentialsId);
+      GitHubRepositoryInfo info = GitHubRepositoryInfo.forRepositoryUrl(repoUrl);
+      GitHub github = Connector.connect(info.getApiUri(), credentials);
+      GHRepository ghRepository =
+          github.getRepository(info.getRepoOwner() + '/' + info.getRepository());
+      return (long) ghRepository.getSize();
+    }
+  }
+}
diff --git a/src/test/java/org/jenkinsci/plugins/github_branch_source/GitHubRepoSizeEstimatorTest.java b/src/test/java/org/jenkinsci/plugins/github_branch_source/GitHubRepoSizeEstimatorTest.java
new file mode 100644
index 000000000..5111ef3a9
--- /dev/null
+++ b/src/test/java/org/jenkinsci/plugins/github_branch_source/GitHubRepoSizeEstimatorTest.java
@@ -0,0 +1,81 @@
+package org.jenkinsci.plugins.github_branch_source;
+
+import static com.github.tomakehurst.wiremock.client.WireMock.*;
+import static com.github.tomakehurst.wiremock.client.WireMock.aResponse;
+import static com.github.tomakehurst.wiremock.client.WireMock.urlEqualTo;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.notNullValue;
+
+import com.cloudbees.plugins.credentials.*;
+import com.cloudbees.plugins.credentials.common.StandardCredentials;
+import com.cloudbees.plugins.credentials.domains.Domain;
+import com.cloudbees.plugins.credentials.impl.UsernamePasswordCredentialsImpl;
+import hudson.model.Item;
+import java.util.Collections;
+import jenkins.model.Jenkins;
+import jenkins.plugins.git.GitToolChooser;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.jvnet.hudson.test.JenkinsRule;
+import org.mockito.Mockito;
+
+@RunWith(Parameterized.class)
+public class GitHubRepoSizeEstimatorTest extends GitSCMSourceBase {
+
+  public GitHubRepoSizeEstimatorTest(GitHubSCMSource source) {
+    this.source = source;
+  }
+
+  @Parameterized.Parameters(name = "{index}: revision={0}")
+  public static GitHubSCMSource[] revisions() {
+    return new GitHubSCMSource[] {
+      new GitHubSCMSource("cloudbeers", "yolo", null, false),
+      new GitHubSCMSource("", "", "https://github.com/cloudbeers/yolo", true)
+    };
+  }
+
+  @Rule public final JenkinsRule j = new JenkinsRule();
+
+  private CredentialsStore store = null;
+
+  @Before
+  public void enableSystemCredentialsProvider() {
+    SystemCredentialsProvider.getInstance()
+        .setDomainCredentialsMap(
+            Collections.singletonMap(Domain.global(), Collections.<Credentials>emptyList()));
+    for (CredentialsStore s : CredentialsProvider.lookupStores(Jenkins.get())) {
+      if (s.getProvider() instanceof SystemCredentialsProvider.ProviderImpl) {
+        store = s;
+        break;
+      }
+    }
+    assertThat("The system credentials provider is enabled", store, notNullValue());
+  }
+
+  @Test
+  public void isApplicableToTest() throws Exception {
+    GitHubRepoSizeEstimator.RepositorySizeGithubAPI api =
+        j.jenkins
+            .getExtensionList(GitToolChooser.RepositorySizeAPI.class)
+            .get(GitHubRepoSizeEstimator.RepositorySizeGithubAPI.class);
+    Item context = Mockito.mock(Item.class);
+    store.addCredentials(Domain.global(), createCredential(CredentialsScope.GLOBAL, "github"));
+    store.save();
+
+    githubApi.stubFor(
+        get(urlEqualTo("/"))
+            .willReturn(
+                aResponse()
+                    .withHeader("Content-Type", "application/json; charset=utf-8")
+                    .withBodyFile("../__files/body-(root)-XwEI7.json")));
+
+    assertThat(api.isApplicableTo(githubApi.baseUrl(), context, "github"), is(false));
+  }
+
+  private StandardCredentials createCredential(CredentialsScope scope, String id) {
+    return new UsernamePasswordCredentialsImpl(scope, id, "desc: " + id, "username", "password");
+  }
+}