play_on

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

With no annotations provided, the description carries the full behavioral burden, and it does so well: it discloses the read/write sequence, the extra write for volume/shuffle via '🟡 (1 read + 1 write; +1 if volume/shuffle)', and the device-name resolution mechanism. It does not mention failure behavior, but the disclosed side effects are unusually clear for a tool without 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?

The description is only two sentences, front-loads the primary action, and packs in endpoint flow, cost characterization, and device matching behavior without waste. Every clause earns its place.

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 10-parameter tool with no output schema and no annotations, the description plus the fully-covered schema is strong: it explains the resolution flow, side-effect count, and accepted input modes. It does not explicitly state mutual exclusivity of query/uris/context_uri, but the schema's 'alternatives' notes and the slash-separated phrasing make that adequately inferable.

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 100%, so the schema already documents every parameter. The description adds the high-level grouping 'context/uris/search query' and restates the device-matching rule, but most of this duplicates schema text such as 'Device name substring (case-insensitive) or exact device id'. This lands at the baseline 3.

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 opens with a specific verb and target: 'Play a context/uris/search query on a named device.' It also names the underlying API flow (GET /me/player/devices, then PUT /me/player/play), which makes the tool's purpose concrete and distinguishes it from generic play tools by emphasizing named-device resolution.

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 phrase 'on a named device' plus 'Supports device name substring or exact id' clearly signals the intended use case: playing when a specific device must be selected. It does not explicitly list siblings like play or transfer_playback as alternatives, so it stops short of full when-to-use versus when-not-to-use guidance.

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