Open WebUI MCP Server

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden. It discloses the ADMIN requirement and lists valid roles, which is helpful. However, it doesn't mention potential side effects (e.g., if role changes affect user access immediately), error conditions, or what the output contains. For a mutation tool with zero annotation coverage, this leaves behavioral gaps.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is extremely concise—three short phrases that are front-loaded with the core purpose. Every sentence earns its place: the first states the action, the second specifies permissions, and the third lists valid values. No wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (a mutation with permission requirements) and the presence of an output schema (which handles return values), the description is reasonably complete. It covers purpose, usage constraints, and parameter semantics. However, without annotations, it could benefit from more behavioral details like side effects or error handling.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, but the description compensates by listing the valid role values ('admin', 'user', 'pending'), which adds meaning beyond the schema's generic 'New role' description. It doesn't explain the 'user_id' parameter, but with only 1 parameter (a nested object with two properties), the description provides useful context for the 'role' field.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the specific action ('Update a user's role') with the resource ('user') and distinguishes it from siblings like 'delete_user' or 'get_user' by focusing on role modification rather than user lifecycle management. It's precise about what the tool does.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It explicitly states 'ADMIN ONLY', providing clear context on when to use this tool (only for administrators) and when not to use it (for non-admins). This directly addresses permission prerequisites, making usage guidelines very clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.