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MCP Server Rules

MCP server rules allow you to provide custom instructions to AI agents when they use tools from a specific MCP server. These rules are automatically applied as a ruleset whenever an agent uses that server's tools, helping ensure consistent and appropriate behavior.

What Are Rules?

Rules are text instructions that guide how the AI agent should interact with a particular MCP server. They're added to the MCP server configuration and automatically applied when:

  • Using the MCPTask node with that server
  • Using the Agent node with that server configured

Why Use Rules?

Rules help you:

  • Guide Agent Behavior: Provide specific instructions on how to use the server's tools
  • Ensure Consistency: Make sure the agent follows your preferred patterns
  • Handle Edge Cases: Instruct the agent on how to handle errors or special situations
  • Optimize Usage: Guide the agent to use the server's capabilities most effectively

Adding Rules to an MCP Server

When Creating a Server

When creating a new MCP server, you can add rules in the Rules text area:

  1. Go to Settings → MCP Servers
  2. Click + New MCP Server
  3. Fill in the server configuration (name, connection type, etc.)
  4. In the Rules text area, enter your custom rules
  5. Click Create Server

When Editing a Server

  1. Go to Settings → MCP Servers
  2. Click the Edit button on the server you want to modify
  3. Modify the text in the Rules text area
  4. Save your changes

Example Rules

For a Web Fetching Server

Always validate URLs before fetching. Check that URLs use HTTPS when possible. If a fetch fails, return a clear error message explaining what went wrong.

For a File System Server

Always check if a file exists before attempting to read it. Use absolute paths when possible. Never delete files without explicit user confirmation.

For a Search Server

Always verify search results are relevant before returning them. If no relevant results are found, suggest alternative search terms. Format results in a clear, readable structure.

For a Database Server

Always validate SQL queries before executing them. Never execute DROP or DELETE operations without explicit confirmation. Return query results in a structured format.

How Rules Work

  1. Storage: Rules are stored as part of the MCP server configuration
  2. Application: When an agent uses tools from that server, the rules are automatically added as a ruleset
  3. Scope: Rules apply only when using that specific MCP server
  4. Format: Rules are a single string - you can include multiple instructions separated by periods or newlines

Best Practices

Be Specific

✅ Good: "Always validate URLs before fetching. Check for HTTPS and return clear error messages."

❌ Vague: "Be careful with URLs."

Focus on Behavior

✅ Good: "Return errors in JSON format with 'error' and 'message' fields."

❌ Too Generic: "Handle errors well."

Keep It Concise

✅ Good: "Validate inputs before processing. Return structured JSON responses."

❌ Too Long: A paragraph explaining every possible scenario in detail.

Test Your Rules

After adding rules, test them with your MCP server to ensure they work as expected:

  1. Create an MCPTask node using the server
  2. Run a test prompt
  3. Verify the agent follows the rules you specified

Rules in Different Contexts

MCPTask Node

When using the MCPTask node, rules from the selected MCP server are automatically applied to the agent that processes the task.

Agent Node

When using the Agent node with MCP servers configured, rules from all enabled MCP servers are collected and applied to the agent.

Troubleshooting

Rules Not Being Applied

  • Verify the rules are entered in the Rules text area (not empty)
  • Check that the server is enabled
  • Ensure you're using the correct server name in your workflow

Agent Not Following Rules

  • Make rules more specific and actionable
  • Test with simpler rules first
  • Check that the rules are appropriate for the server's capabilities

Next Steps