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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context beyond that: it explains the return shape as one row of the Tracking page with broadcast and private messages, and notes the required API key access. It does not cover rate limits or pagination, but for a read tool this is solid added 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 front-loaded with the purpose and then layers return details, usage, and auth requirements in four compact sentences. The redundant 'Paperless Post:' prefix is minor, and every sentence contributes something useful. It is not maximally tight but is well structured.

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 simple two-parameter read tool with annotations covering safety and no output schema, the description supplies the missing return-value context, a usage rationale, and the auth prerequisite. An agent has enough to call it correctly without needing to infer return semantics or access requirements.

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 coverage is 100%, and both event_id and guest_id are documented in the schema with source hints. The description does not add syntax, format, or validation details beyond what the schema already provides, so the baseline 3 is appropriate when the schema carries the parameter semantics.

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 ('Get guest', 'One guest') and scopes the return to status, number attending, and messages sent. It also distinguishes this from write-oriented siblings by framing the purpose as checking what a guest already received before writing again. An agent can identify this as a single-guest read operation without opening the schema.

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 gives clear usage context: 'Use it to check what a guest already received before you write again.' This tells the agent when the tool is valuable relative to send_message or send_private_message, but it does not explicitly name an alternative or state when not to use it. The guidance is clear but lacks exclusionary detail.

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