Auto-translate Forum Posts

In this tutorial, you will create a webhook-triggered agent that automatically translates new forum posts into another language and posts the translation as a reply.

Time: 20 minutes Requirements: Harness plan or higher, one connected forum site with webhook support

What You Will Build

A webhook-triggered agent that:

1. Receives a notification when a new post is created on your forum
2. Reads the original post
3. Translates it to the target language
4. Posts the translation as a reply in the same thread

Step 1: Connect Your Forum

Ensure your forum site is connected in the vault with tools that include:

• get_thread or get_post — to read posts
• create_post — to post translations

Step 2: Create the Agent

1. Go to Agents > New Agent.
2. Configure:

Field	Value
Name	Post Translator (EN to ES)
Description	Translates new English posts to Spanish
Model	GPT-4o Mini (cost-effective for translation)
Sites	Your forum site
Max Rounds	3
Trigger	Webhook

3. Enter the system prompt:

You are a translation assistant for our bilingual community forum.

TASK:
When a new post is created (provided in the webhook payload):
1. Read the post content using the get_thread tool with the 
   provided thread_id.
2. Translate the post content from English to Spanish.
3. Post the translation as a reply using the create_post tool.

TRANSLATION RULES:
- Maintain the original formatting (paragraphs, lists, bold, etc.)
- Preserve technical terms, product names, and URLs unchanged.
- Add a note at the top: "[Translated from English]"
- If the post is already in Spanish, do NOT translate. 
  Just output "Post is already in Spanish — skipping."

USE THE WEBHOOK DATA:
- thread_id: from the webhook payload
- post_id: from the webhook payload (for reference)

4. Click Create.
5. Copy the Webhook URL and Webhook Secret that appear after saving.

Step 3: Configure the Webhook Schema

In the agent editor, define the expected webhook payload:

Field	Type	Description
event	string	Event type (e.g., "new_post")
thread_id	number	The thread containing the new post
post_id	number	The new post ID
author	string	Post author username
content_preview	string	First 200 characters of the post

Step 4: Configure Your Forum's Webhook

In your forum's admin panel (the exact steps depend on your platform):

1. Navigate to the webhook or notification settings.

2. Add a new webhook:

   • URL: the agent's webhook URL from Step 2
   • Secret: the webhook secret from Step 2 (sent as X-Webhook-Secret header)
   • Events: new post created
   • Content Type: application/json

3. Configure the payload to match the schema:

{
  "event": "new_post",
  "thread_id": 12345,
  "post_id": 67890,
  "author": "john_doe",
  "content_preview": "Hello everyone, I wanted to share..."
}

Step 5: Test the Integration

Manual Test with curl

curl -X POST "https://webmcp-master.ai/api/webhooks/agent/YOUR_AGENT_ID" \
  -H "Content-Type: application/json" \
  -H "X-Webhook-Secret: YOUR_SECRET" \
  -d '{
    "event": "new_post",
    "thread_id": 12345,
    "post_id": 67890,
    "author": "test_user",
    "content_preview": "This is a test post for translation."
  }'

Check the Run

1. Go to Agents > Post Translator > Runs.
2. Verify the run:
   • Status: Done
   • Steps: read the post, translate, post the reply
   • Credit usage: typically 1-3 credits with GPT-4o Mini

Verify on the Forum

Check the forum thread to confirm the translated reply was posted with the "[Translated from English]" header.

Step 6: Handle Edge Cases

Update the system prompt to handle:

• Already translated posts: Check if a translation reply already exists before creating a duplicate.
• Non-English posts: Detect the language first; only translate English posts.
• Very long posts: If the post exceeds 5,000 characters, summarize and translate.
• Posts with images: Note that images cannot be translated; preserve image references as-is.

Cost Estimate

Using GPT-4o Mini with 3 max rounds:

• Per translation: approximately 0.5-1.5 credits
• At 50 new posts per day: ~25-75 credits/day (~750-2,250 credits/month)

TIP

GPT-4o Mini provides excellent translation quality at very low cost. Switching to a more expensive model is unnecessary for most translation tasks.

Troubleshooting

Issue	Solution
Webhook returns 401	Verify the webhook secret matches exactly
Agent does not post the reply	Check that the create_post tool is not on the deny list
Duplicate translations	Add a check in the prompt to look for existing translation replies
Wrong language detected	Add explicit language detection instructions to the prompt