update_now_playing

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

Annotations already provide idempotent and non-destructive hints, but the description adds useful context: authentication is required and Last.fm clears the now playing line on its own shortly after. This goes beyond the structured annotations without contradicting them.

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 front-loaded with the core purpose, followed by a brief clarification about scrobbling and a scannable Args block. There is no filler or repetition of schema information.

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 output schema exists and annotations provide safety hints, the description covers the essential call context: purpose, auth requirement, non-scrobble behavior, and all parameter semantics. It could add error behavior or authentication-state details, but those are not necessary for a basic correct invocation.

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 Args list carries the full burden. It documents all seven parameters, including units for duration, the conditional meaning of album_artist, and what mbid represents. The entries are terse but genuinely informative.

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 states a clear verb and resource: 'Set what is playing right now' and explicitly says it only updates the 'now playing' line. It also differentiates itself from scrobbling, which is a key distinction among the sibling tools.

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 clearly says authentication is needed and explicitly states it does not scrobble, which helps an agent avoid using it as a scrobble replacement. However, it does not explicitly name the alternative tool like scrobble_tracks or describe sequencing.

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