start_authentication

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

Annotations already cover the read/write safety profile and idempotency. The description adds valuable behavioral context: it returns a token and a browser URL, requires user approval, and must be followed by finish_authentication with the same token. This goes beyond the structured hints and gives the agent a clear picture of the flow.

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 tightly written sentences: the first states the action, the second explains the immediate output and user step, and the third specifies the prerequisite context. No filler or repetition. Information is front-loaded and each sentence 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 tool with no parameters, an output schema available, and clear sibling context, the description is fully sufficient. It explains what is returned, what the agent/user must do next, and when the tool is required. Nothing essential is 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?

The tool has zero parameters, and the schema description coverage is 100%, so there are no parameter gaps to compensate for. The description adds relevant flow-level semantics (token usage) even though no parameters exist, earning the 0-parameter baseline of 4.

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 uses a specific verb ('Begin') and resource ('Last.fm desktop auth flow'), clearly identifying the tool's function. It distinguishes itself from sibling authentication tools by framing the flow's first step and referencing finish_authentication as the follow-up.

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 this tool is needed ('Only needed for writes: scrobbling, loving, and tagging'), which implicitly tells agents not to use it for read-only operations. It also provides a clear next-step instruction to call finish_authentication with the returned token.

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