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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered structurally. The description adds a scope disclosure about what is intentionally omitted (body, recipient details), but says nothing about ordering, pagination, or how many events are returned.

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?

A single sentence with zero filler, front-loading the resource and immediately qualifying the scope with the exclusion clause. 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 simple read-only lookup with full schema coverage, complete annotations, and no output schema, the description is sufficient: an agent knows what it gets (event timeline) and what it will not get. Minor gap is the absence of any return-shape or ordering hint.

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%: the schema already documents 'id' as the Message ID and 'apiKey' as the key override. The description adds no format, prefix, or lookup guidance beyond that, so the baseline of 3 applies.

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?

States a specific verb and resource (get the delivery event timeline for a message) and scopes it by exclusion ('no body or recipient details'), which implicitly separates it from the sibling get_message. It stops short of naming get_message explicitly, so sibling differentiation is inferable rather than stated.

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?

Usage is implied by the scoping phrase: reach for this when you only need the event timeline, not the full message. However, no alternative tool is named and no explicit when-not condition is given (e.g. 'if you also need the body, use get_message').

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