search_and_play

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

Annotations already indicate this is a non-read-only mutation (readOnlyHint=false), so the description's 'play' action is consistent. The description adds meaningful behavior beyond annotations: if no active device is available, Vela opens the local Spotify app and registers this PC as a playback device before retrying. This discloses a side effect that an agent could not infer from the schema or annotations.

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?

Three sentences, each with a distinct job: core action, fallback behavior, and usage trigger. No filler or redundancy. The core function 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 tool with no output schema and only two parameters, the description covers the main action and an important fallback. However, it omits likely prerequisites such as Spotify authentication (siblings spotify_auth and spotify_callback suggest an auth flow exists) and does not describe behavior when the search finds no matching song. These are meaningful gaps for an agent invoking the 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 description must compensate. It implies the query parameter is the search string ('Search Spotify for a song'), but it never explicitly maps device_id to a parameter or explains how a caller would target a specific device. The fallback discussion of 'no active device' is related but does not clarify the purpose of the device_id argument.

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 specific verb and resource: 'Search Spotify for a song and immediately play it.' It also specifies the intended user need ('when the user wants to hear a specific song'), which clearly distinguishes this tool from playback control siblings like toggle_play_pause, next_track, or get_currently_playing_song.

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 tells when to use the tool: 'Use when the user wants to hear a specific song.' This is clear context, but it does not name alternatives or explain when not to use it, such as when a song is already playing and the user only wants to resume it.

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