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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds the useful sort order ('newest first') but says nothing about pagination depth, default page size, or what a result set contains beyond the filters.

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?

Two short sentences with no filler; the ordering guarantee is front-loaded before the filter list, which is exactly the priority an agent needs.

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 14-parameter, zero-required, read-only listing tool with no output schema, the description plus annotations and a well-documented schema cover enough to call it correctly. The gap is pagination and result-shape expectations, which the schema's cursor/limit hints only partially fill.

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 86%, so the schema already carries per-parameter semantics, and the baseline of 3 applies. The description does summarize the filterable axes (number, direction, status, failure reason, date, schedule, customer) but omits limit/cursor and adds no syntax or interaction details such as blocked_reason implying status=blocked.

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 ('List your messages') plus an ordering guarantee ('newest first'), which an agent can't infer from the name alone. It does not explicitly distinguish itself from the get_message sibling, so it stops short of a 5.

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 enumeration of filter axes implies when this tool is the right choice ('I need messages matching X'), but it never states exclusions or names alternatives such as get_message for a single message or list_scheduled_messages for pending sends. Usage is inferable rather than directed.

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