Calling Your MCP Server From an n8n Flow

Lesson 2 got WordPress events into n8n. This lesson runs the flow the other way: an n8n workflow reaching back into WordPress to do something, either through the MCP server you built in Course 2, or through n8n’s native WordPress node when the job is a plain post, page, or user operation that doesn’t need an ability at all.

Step 1: Decide which path you actually need

n8n ships a real, native WordPress node covering three resources: Post, Page, and User, each with create, get, get all, and update operations. If the job in front of you is “create a page,” “update a post,” or “get a user,” use that node directly, it’s less setup than driving the MCP protocol by hand. It does not cover comments, media, categories, or anything defined as a custom ability, for any of that, or for calling a specific registered ability by name, you need the HTTP Request node against your MCP server instead.

Step 2: Set up the WordPress node credential

Add a WordPress node, and on its credential screen choose the basic-auth option. It asks for your WordPress username, an Application Password (the same one from Users → Profile → Application Passwords in wp-admin), and your site’s URL. This is the same authentication model the MCP Adapter itself relies on, one Application Password covers both paths.

For simple operations, that’s the whole setup: choose Resource (Post/Page/User), Operation (Create/Get/Get All/Update), fill in the fields, done.

Step 3: Drive the MCP session with HTTP Request nodes

For a specific ability, you need three chained HTTP Request nodes, mirroring the same session protocol from Course 2’s HTTP transport lesson, just driven from n8n instead of curl.

Node 1, Initialize:

// n8n HTTP Request node body (JSON)
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "initialize",
  "params": {
    "protocolVersion": "2025-11-25",
    "capabilities": {},
    "clientInfo": { "name": "n8n-workflow", "version": "1.0.0" }
  }
}

Set Authentication to the Application Password credential (Basic Auth, generic credential type), Method to POST, URL to https://yoursite.example.com/wp-json/my-plugin/content-mcp, and under Options, enable “Include Response Headers and Status.” That last setting is what lets the next node read Mcp-Session-Id out of the response at all.

Node 2, notifications/initialized, add a header field:

Name: Mcp-Session-Id
Value: {{ $node["Initialize"].json["headers"]["mcp-session-id"] }}

with body:

{ "jsonrpc": "2.0", "method": "notifications/initialized" }

Node 3, tools/call, same Mcp-Session-Id header expression, body naming the ability (recall from Course 2 that a slash in the ability name becomes a hyphen in the MCP tool name):

{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "tools/call",
  "params": {
    "name": "my-plugin-create-draft-post",
    "arguments": { "title": "Drafted from n8n", "content": "Body text here." }
  }
}

Step 4: Test it

Run the three-node chain manually in n8n (the “Execute step” button on each node), and confirm node 3’s output includes a successful result rather than a JSON-RPC error object. Then check wp-admin for the new draft post. If node 3 fails with a session-related error, re-check node 2 actually fired and that the header expression in node 3 points at node 1’s output, not node 2’s, since only the initialize response carries the Mcp-Session-Id header in the first place.

Recap

n8n’s native WordPress node handles Post, Page, and User create/get/get all/update without any MCP protocol involved, use it whenever the job fits. For a specific registered ability, chain three HTTP Request nodes: initialize (capturing the Mcp-Session-Id response header), notifications/initialized, and tools/call naming the ability and its arguments, all authenticated with the same WordPress Application Password either path uses. The next lessons build on this outbound call as one step in larger, multi-node workflows.

Resources & further reading

• n8n WordPress node documentation, docs.n8n.io
• n8n HTTP Request node documentation, docs.n8n.io
• MCP Adapter repository, GitHub
• Model Context Protocol specification