Last.fm MCP Server

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

With no annotations provided, the description carries full burden and does well by disclosing the tool's read-only nature (it only checks status, doesn't modify anything) and its binary return behavior. However, it doesn't mention potential error conditions, rate limits, or authentication persistence details that could be relevant for an agent.

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 structured: first sentence states purpose, second provides crucial usage context with specific tool list, then clearly documents parameters and return values. Every sentence earns its place with zero wasted words, and the most important information (purpose and usage) is front-loaded.

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?

For a zero-parameter tool with an output schema (implied by the return documentation), the description is complete: it explains purpose, provides essential usage guidelines, documents the parameter situation, and specifies return values. No additional information is needed for an agent to use this tool effectively.

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 schema has 0 parameters with 100% coverage, so the baseline would be 3. The description explicitly states 'Args: None', which adds value by confirming no parameters are needed beyond what the empty schema indicates. This clarity about parameter absence justifies a higher score.

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 tool's purpose with a specific verb ('Check') and resource ('if the user is authenticated'), distinguishing it from sibling tools that perform actions requiring authentication rather than checking status. It goes beyond the name by specifying what authentication status means in this context.

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 explicitly lists six tools that require authentication, providing clear guidance on when this tool should be used (before invoking those tools) and alternatives (the authenticate_user tool for obtaining authentication). This directly addresses when-to-use vs. alternatives.

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