Model Context Protocol (MCP) Setup

Mostly provides a native Model Context Protocol (MCP) server over standard HTTP JSON-RPC 2.0. This allows AI coding assistants like Cursor, Claude Desktop, and Antigravity to directly inspect your brand constitution, query winning competitor ads, and trigger script generation workflows.

1. Prerequisites

1. Generate an API Key in Settings → API & MCP.
2. Ensure your key starts with mst_live_.

2. Configuration for Cursor IDE

Add the following to your project's .cursor/mcp.json (or your Global Cursor Settings):

{
  "mcpServers": {
    "mostly": {
      "url": "https://mostly.so/api/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_MOSTLY_API_KEY"
      }
    }
  }
}

3. Configuration for Claude Desktop

Add this configuration block to your claude_desktop_config.json:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "mostly": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://mostly.so/api/mcp",
        "--header",
        "Authorization: Bearer YOUR_MOSTLY_API_KEY"
      ]
    }
  }
}

4. Testing with cURL

You can test the MCP endpoint directly using standard JSON-RPC 2.0:

List Available Tools (tools/list)

curl -X POST https://mostly.so/api/mcp \
  -H "Authorization: Bearer mst_live_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "tools/list"
  }'

Call a Tool (tools/call)

curl -X POST https://mostly.so/api/mcp \
  -H "Authorization: Bearer mst_live_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 2,
    "method": "tools/call",
    "params": {
      "name": "search_creatives",
      "arguments": {
        "query": "skincare routine",
        "isViralOutlier": true,
        "limit": 5
      }
    }
  }'

5. Choosing a Brand

Brand tools (brand kit, pages, documents, memory, BRAND.md, skills, keywords, slide decks) act on one brand:

• One brand in the workspace: it's used automatically.
• Several brands: call list_brands, then either pass brandId in each tool's arguments, or set a default for the connection with the X-Mostly-Brand-Id header (or ?brandId= on the URL).

{
  "mcpServers": {
    "mostly": {
      "url": "https://mostly.so/api/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_MOSTLY_API_KEY",
        "X-Mostly-Brand-Id": "YOUR_BRAND_ID"
      }
    }
  }
}

6. Live Tool Catalog

When connected via MCP, your AI assistant automatically gains access to: