Auto-Generate AI Social Captions from WordPress Blogs to Four Platforms

WordPress publish → n8n webhook trigger → AI generates platform-specific captions → parallel publish to X, Facebook, Instagram, LinkedIn

Who

Content creators, digital marketing agencies, SEO teams, and businesses publishing blog content regularly

You get

Every WordPress blog post automatically gets four platform-optimized social captions and publishes simultaneously without manual rewriting

You need

n8n

Steps

1. Configure WordPress Webhook Trigger

   Install the WP Webhooks plugin (free, wordpress.org/plugins/wp-webhooks) on your WordPress site. Go to Settings → WP Webhooks → Send Data, add a new webhook, select trigger Post Published or Post Updated, and paste your n8n Webhook node URL as the delivery URL. Save and test by publishing a blog post; verify the n8n Webhook node receives a POST request containing post_title, post_content, post_type, post_status, post_permalink, and post_thumbnail.

2. Set Up Conditional Filtering and Data Normalization

   Configure the If node with two conditions: post_type equals 'post' AND post_status equals 'publish', ensuring only published blog posts proceed. Then configure the Clean Data (Set) node to map fields from the Webhook: post_title, post_content (from HTML To Markdown output), post_link, post_thumbnail. Replace the hardcoded facebook_page_id and instagram_id with your real IDs (the workflow.json currently contains placeholder values 788563884350153 and 17841478701285041).

3. Convert HTML to Markdown

   Add the HTML To Markdown node, with input from the Webhook's post.post_content. This removes HTML tags, shortcodes, and formatting markup, providing clean text to the AI and avoiding quality degradation from raw HTML.

4. Configure AI Agent Prompt and Model

   The AI Agent node uses the OpenRouter Chat Model (default openai/gpt-4o; switchable to Claude, Gemini, Mistral, etc.). Configure as follows:

   Execution prompt · Source text。AI Agent node User Message / Text field

   Copy prompt

   =Post Title: {{ $json.post_title }}
   Post Link: {{ $json.post_link }}
   Post Content: {{ $json.post_content.slice(0, 800) }}
   
   Generate platform-specific social media captions for this blog post now.

   Execution prompt · Source text。AI Agent node System Message / Options field

   Copy prompt

   # Role
   You are a professional social media content writer.
   You write platform-specific captions when a new blog 
   post is published on a WordPress website.
   
   # Your Job
   Read the post title, link, and content.
   Then write one caption for each platform below.
   Each caption must match that platform's style, 
   tone, length, and best practices.
   
   # Platform Guidelines
   
   TWITTER:
   - Max 220 characters including the link
   - One punchy insight or hook from the post
   - 1 to 2 relevant hashtags only
   - End with the post link
   - Tone: short, direct, conversational
   
   FACEBOOK:
   - Max 300 characters for the hook line
   - Start with a bold question or statement
   - 2 to 3 bullet points of what readers will learn
   - End with the post link
   - Tone: friendly, conversational
   - No more than 3 hashtags
   
   INSTAGRAM:
   - Start with a bold hook in the first 125 characters
   - 3 to 5 key takeaways as short bullet points
   - End with: Link in bio to read the full guide
   - Add 3 to 5 relevant hashtags at the bottom
   - Tone: engaging, direct, value-driven
   - Do NOT include the link in the caption body
   
   LINKEDIN:
   - Professional tone
   - Start with a bold insight or surprising statement
   - Write 3 to 4 short paragraphs:
     Paragraph 1: the hook or problem
     Paragraph 2: what the post covers
     Paragraph 3: key takeaway or insight
     Paragraph 4: call to action with the link
   - 2 to 3 professional hashtags at the end
   - Between 800 and 1200 characters total
   
   # Output Format
   Return ONLY a valid JSON object.
   No explanation. No markdown. No extra text.
   Just the raw JSON like this:
   
   {
     "twitter": "your twitter caption here",
     "facebook": "your facebook caption here",
     "instagram": "your instagram caption here",
     "linkedin": "your linkedin caption here"
   }

5. Configure Structured Output Parser

   Connect the Structured Output Parser to the AI Agent. Set the JSON Schema example to {"twitter": "string", "facebook": "string", "instagram": "string", "linkedin": "string"} to enforce valid JSON output, ensuring downstream publishing nodes can reliably extract each platform's caption.

6. Configure Social Media Publishing Nodes

   Configure four parallel publishing branches: **Twitter/X**: Create Tweet node, text set to {{ $json.output.twitter }}, connected to twitterOAuth2Api credentials. **Facebook**: HTTP Request node, POST to https://graph.facebook.com/v25.0/{{ $('Clean Data').item.json.facebook_page_id }}/photos, query parameters message={{ $json.output.facebook }} and url={{ $('Clean Data').item.json.post_thumbnail }}, using httpQueryAuth credentials (Facebook Page Access Token). **Instagram**: Two-step official Meta flow. Step one: Create Media Container, POST to /{{ instagram_id }}/media, parameters caption={{ $json.output.instagram }} and image_url={{ post_thumbnail }}. Step two: Post On IG, POST to /{{ instagram_id }}/media_publish, parameter creation_id={{ $json.id }} (from step one response). Both use the same httpQueryAuth credentials. **LinkedIn**: First add an HTTP Request node to download the post_thumbnail image as binary (LinkedIn requires binary image data, not a URL). Then the Create a post node, text set to {{ $json.output.linkedin }}, postAs=organization, organization replaced with your real URN (currently placeholder 'your_org_URN'), shareMediaCategory=IMAGE, connected to linkedInOAuth2Api credentials.

7. Test and Verify Publishing

   Publish a test blog post on WordPress and check the n8n execution log to confirm: If node passes, HTML To Markdown succeeds, AI Agent returns valid JSON, and all four platforms receive content. If any platform fails, verify the corresponding credentials permissions, API rate limits, and that the image URL is publicly accessible.

You are an n8n workflow setup assistant. The user wants to replicate a template that auto-syncs WordPress blogs to four social media platforms. First confirm the user has: WordPress admin access, WP Webhooks plugin, a publicly accessible n8n instance, an OpenRouter API key, and API credentials for all four social platforms. Then guide them to import or manually rebuild the workflow, with special attention to replacing the facebook_page_id, instagram_id, and LinkedIn organization URN in the Clean Data node with real values. Finally, remind them to test with a draft or private post first.