Last.fm MCP Server

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

No annotations are provided, so the description carries full burden. It discloses the tool's role in authentication (obtaining a session key after user authorization) but lacks details about error conditions (e.g., invalid token, expired authorization), rate limits, or what the session key enables. The description adds basic behavioral context but misses important operational details.

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 perfectly concise with two sentences that each earn their place: the first states the purpose, the second provides crucial usage guidance. There is zero wasted text, and the information is front-loaded with the core function.

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 (authentication step), lack of annotations, and presence of an output schema, the description is reasonably complete. It explains the tool's role in the workflow and prerequisite, though it could benefit from mentioning what the session key enables or common failure modes. The output schema will handle return values, so that gap is acceptable.

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?

The tool has 0 parameters with 100% schema description coverage. The description appropriately doesn't discuss parameters since none exist, and it correctly focuses on the tool's purpose and usage context. This meets the baseline expectation for parameterless tools.

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 ('Complete the authentication process by getting a session key') and resource ('from the authorized token'), distinguishing it from siblings like authenticate_user (which provides the authorization URL) and check_auth_status (which likely checks authentication state). It explicitly defines the tool's role in the authentication workflow.

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?

The description provides explicit guidance on when to use this tool: 'after the user has visited the authorization URL from authenticate_user()'. It names the prerequisite tool (authenticate_user) and specifies the exact sequence in the authentication flow, clearly differentiating it from alternatives like check_auth_status.

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