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 the full burden. It discloses key behavioral traits: it's a mutation tool (implied by 'Love a track'), requires authentication (explicitly stated), and returns a confirmation. However, it lacks details on error handling, rate limits, or side effects (e.g., impact on Last.fm recommendations), leaving some gaps in behavioral context.

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 appropriately sized and front-loaded: the first sentence states the purpose, the second provides critical usage guidelines, and the args/returns sections are structured clearly. Every sentence adds value without redundancy, making it efficient and easy to parse.

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 moderate complexity (mutation with authentication), no annotations, and an output schema (which handles return values), the description is mostly complete. It covers purpose, prerequisites, and parameters at a high level, but lacks details on error cases or behavioral nuances, leaving minor gaps for a mutation tool.

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%, so the schema provides no parameter details. The description adds minimal semantics by listing 'artist' and 'track' as args and briefly describing them, but it doesn't explain format (e.g., case sensitivity), constraints, or examples. This partially compensates for the schema gap but is insufficient for full clarity, aligning with the baseline for moderate coverage issues.

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 action ('Love a track') and the target resource ('on your Last.fm profile'), using a specific verb. It distinguishes this tool from sibling tools like 'unlove_track' (which reverses the action) and 'get_user_loved_tracks' (which reads rather than modifies loved tracks), making the purpose explicit and differentiated.

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 specifying prerequisites: 'Requires authentication - use authenticate_user() and get_session() first.' It also implies usage context (modifying loved tracks) and distinguishes it from alternatives like 'unlove_track' for unloving or 'get_user_loved_tracks' for viewing, providing clear guidance.

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