While Probot doesn't have an official extension API, there are a handful of reusable utilities that have been extracted from existing apps.


probot-commands is an extension that adds slash commands to GitHub. Slash commands are lines that start with / in comments on Issues or Pull Requests that allow users to interact directly with your app.

For example, users could add labels from comments by typing /label in-progress.

import commands from "probot-commands";

export default (app) => {
  // Type `/label foo, bar` in a comment box for an Issue or Pull Request
  commands(app, "label", (context, command) => {
    const labels = command.arguments.split(/, */);
    return context.octokit.issues.addLabels(context.issue({ labels }));


probot-metadata is an extension that stores metadata on Issues and Pull Requests.

For example, here is a contrived app that stores the number of times that comments were edited in a discussion and comments with the edit count when the issue is closed.

import metadata from "probot-metadata";

export default (app) => {
  app.on(["issues.edited", "issue_comment.edited"], async (context) => {
    const kv = await metadata(context);
    await kv.set("edits", (await kv.get("edits")) || 1);

  app.on("issues.closed", async (context) => {
    const edits = await metadata(context).get("edits");
        body: `There were ${edits} edits to issues in this thread.`,


probot-attachments adds message attachments to comments on GitHub. This extension should be used any time an app is appending content to user comments.

import attachments from "probot-attachments";

export default (app) => {
  app.on("issue_comment.created", (context) => {
    return attachments(context).add({
      title: "Hello World",
      title_link: "https://example.com/hello",

Check out probot/unfurl to see it in action.

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