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 clearly states the authentication requirement and the optional timestamp behavior (defaults to current time). However, it doesn't mention potential rate limits, error conditions, or what happens if the track isn't found, 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 efficiently structured with a clear purpose statement, usage prerequisites, parameter explanations, and return value description in just a few sentences. Every sentence adds value without redundancy, and information is appropriately 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 write operation with no annotations and 6 parameters, the description does well by covering authentication needs, parameter semantics, and basic behavior. However, it lacks details about error handling, rate limits, or validation rules. The presence of an output schema means return values don't need explanation, but some behavioral context remains missing.

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 explaining all 6 parameters in detail. It clarifies that 'artist' and 'track' are required, 'timestamp' defaults to current time, 'album' and 'duration' are optional, and 'mbid' provides more accuracy than name. This adds significant value beyond the bare schema.

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 ('scrobble a track') and resource ('to your Last.fm profile'), distinguishing it from siblings like 'update_now_playing' (which updates current playback) or 'love_track' (which marks a track as loved). It specifies the exact operation rather than being vague or tautological.

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 ('for a specific timestamp or current time') and provides clear prerequisites ('Requires authentication - use authenticate_user() and get_session() first'). It also implicitly distinguishes from 'update_now_playing' by handling past timestamps, offering explicit guidance on context and alternatives.

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