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

Annotations only declare readOnlyHint, so the description does usefully add that start/end/sent_at/delivered_at accept UNIX timestamps, ISO 8601, or plain English - a non-obvious behavior documented nowhere in the schema. However, it says nothing about result ordering, auth requirements, rate limits, or how pagination behaves across a large report set, so this is added context rather than rich behavioral disclosure.

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?

Front-loaded with the core purpose, then use case, then date syntax, then the REST mapping - a sensible ordering with little waste. The parenthetical list of seven returned fields is slightly run-on but earns its place given there is no output schema.

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 read-only, 10-parameter filter tool with no output schema, the description covers purpose, use case, date filter semantics, and the returned field set. The remaining omissions (ordering, pagination behavior) are secondary and the schema carries the per-parameter limits.

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 already 100%, so the baseline is 3, but the description goes further by explaining the accepted date formats for the four date-ish filters, which the schema descriptions ("Start of the date range to filter on.") omit entirely. That is meaningful supplemental guidance for the trickiest parameters.

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?

"List delivery reports of sent messages" gives a specific verb + resource, and the parenthetical field enumeration plus "GET /report" pins down exactly what data comes back. It implicitly but clearly separates itself from siblings like list_inbox (inbound) and list_scheduled_messages (future sends).

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?

"Use it to check whether a message was delivered" supplies an explicit context of use, which is more than most siblings offer. It stops short of naming alternatives or stating when NOT to use it (e.g. for inbound messages, use list_inbox), so it does not reach a 5.

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