Last.fm MCP Server

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively communicates the authentication requirement, which is a critical behavioral trait. However, it doesn't mention potential rate limits, error conditions, or what happens if the update fails, leaving some behavioral aspects uncovered.

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 and concise: a clear purpose statement, essential usage guidance, and well-organized parameter documentation. Every sentence earns its place with no wasted words, and the information is front-loaded appropriately.

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 complexity of an authenticated write operation with 5 parameters and no annotations, the description provides excellent coverage: clear purpose, authentication requirements, parameter semantics, and return value indication. With an output schema present, the description appropriately doesn't need to detail return values.

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?

With 0% schema description coverage, the description fully compensates by clearly documenting all 5 parameters, their purposes, and which are required vs. optional. The parameter documentation in the description adds complete semantic meaning beyond what the bare schema provides.

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 your "now playing" status') and resource ('on Last.fm'), distinguishing it from sibling tools like 'scrobble_track' or 'love_track' which perform different actions. The verb 'update' is precise and the scope is well-defined.

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 states when to use this tool by providing prerequisites ('Requires authentication - use authenticate_user() and get_session() first'), which is crucial guidance. It also implicitly distinguishes it from other status-related tools by focusing on real-time 'now playing' updates rather than historical data like 'get_user_recent_tracks'.

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