Triggers

Triggers allow your app to automatically respond to specific events or actions within a Reddit community. Use triggers to build automation, moderation, and engagement features that react to user or moderator activity.

What are triggers?

A trigger is an action you can build into your app that will occur automatically when a specified condition is met. For example, you can set up a trigger to respond when a new post is submitted, a comment is created, or a moderator takes action.

Supported trigger types

Event triggers let your app automatically respond to a user's or moderator's action. The following trigger types are supported:

• onPostSubmit
• onPostCreate
• onPostUpdate
• onPostReport
• onPostDelete
• onPostFlairUpdate
• onCommentCreate
• onCommentDelete
• onCommentReport
• onCommentSubmit
• onCommentUpdate
• onPostNsfwUpdate
• onPostSpoilerUpdate
• onAppInstall
• onAppUpgrade
• onModAction
• onModMail
• onAutomoderatorFilterPost
• onAutomoderatorFilterComment
• onMentionInCommentCreate

A full list of events and their payloads can be found in the EventTypes documentation. For more details on Mod specific actions, see ModActions and ModMail.

Setting up triggers

1. Add triggers and endpoints to devvit.json

Declare the triggers and their corresponding endpoints in your devvit.json:

"triggers": {
  "onAppUpgrade": "/internal/on-app-upgrade",
  "onCommentCreate": "/internal/on-comment-create",
  "onPostSubmit": "/internal/on-post-submit"
}

2. Handle trigger events in your server logic

Listen for the events in your server and access the data passed into the request:

Hono

server/index.ts

import type {
  OnAppUpgradeRequest,
  OnCommentCreateRequest,
  OnPostSubmitRequest,
  TriggerResponse,
} from '@devvit/web/shared';

app.post('/internal/on-app-upgrade', async (c) => {
  console.log('Handle event for on-app-upgrade!');
  const input = await c.req.json<OnAppUpgradeRequest>();
  const installer = input.installer;
  console.log('Installer:', JSON.stringify(installer, null, 2));
  return c.json<TriggerResponse>({ status: 'ok' });
});

app.post('/internal/on-comment-create', async (c) => {
  console.log('Handle event for on-comment-create!');
  const input = await c.req.json<OnCommentCreateRequest>();
  const comment = input.comment;
  const author = input.author;
  console.log('Comment:', JSON.stringify(comment, null, 2));
  console.log('Author:', JSON.stringify(author, null, 2));
  return c.json<TriggerResponse>({ status: 'ok' });
});

app.post('/internal/on-post-submit', async (c) => {
  console.log('Handle event for on-post-submit!');
  const input = await c.req.json<OnPostSubmitRequest>();
  const post = input.post;
  const author = input.author;
  console.log('Post:', JSON.stringify(post, null, 2));
  console.log('Author:', JSON.stringify(author, null, 2));
  return c.json<TriggerResponse>({ status: 'ok' });
});

Express

server/index.ts

import type {
  OnAppUpgradeRequest,
  OnCommentCreateRequest,
  OnPostSubmitRequest,
  TriggerResponse,
} from '@devvit/web/shared';

const router = express.Router();

// ..

router.post<string, never, TriggerResponse, OnAppUpgradeRequest>(
  "/internal/on-app-upgrade",
  async (req, res) => {
  console.log(`Handle event for on-app-upgrade!`);
  const installer = req.body.installer;
  console.log("Installer:", JSON.stringify(installer, null, 2));
  res.status(200).json({ status: "ok" });
});

router.post<string, never, TriggerResponse, OnCommentCreateRequest>(
  "/internal/on-comment-create",
  async (req, res) => {
  console.log(`Handle event for on-comment-create!`);
  const comment = req.body.comment;
  const author = req.body.author;
  console.log("Comment:", JSON.stringify(comment, null, 2));
  console.log("Author:", JSON.stringify(author, null, 2));
  res.status(200).json({ status: "ok" });
});

router.post<string, never, TriggerResponse, OnPostSubmitRequest>(
  "/internal/on-post-submit",
  async (req, res) => {
  console.log(`Handle event for on-post-submit!`);
  const post = req.body.post;
  const author = req.body.author;
  console.log("Post:", JSON.stringify(post, null, 2));
  console.log("Author:", JSON.stringify(author, null, 2));
  res.status(200).json({ status: "ok" });
});

Best practices

• Avoid creating recursive triggers that could cause infinite loops or crashes (for example, a comment trigger that creates a comment).
• Always check the event payload to ensure your app is not the source of the event before taking action.
• Review the EventTypes documentation for details on event payloads.

caution

Triggers are not guaranteed to deliver only once for a single event. Ensure your app logic is able to handle this case, e.g. checking if content has been recently actioned before taking action again.