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

With only readOnlyHint available, the description carries behavioral weight and delivers: the default 10-day window, the full status vocabulary including status.detail, MT/MO semantics, the pagination protocol (pass next_page as page), and the underlying GET /sms/v1/messages endpoint. It does not disclose result-count totals or behavior when the window exceeds 10 days, which keeps it short of a 5.

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-loads the return content, then defaults, then filters, then pagination and endpoint – a logical order with no filler sentences. The opening sentence is dense with parenthetical statuses but every clause carries information 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?

No output schema exists, yet the description already enumerates the returned fields and the delivery-status states, and all 11 optional parameters are documented in the schema with 100% coverage. Gaps are minor: no error/empty-result behavior and no guidance on large window handling.

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%, so the baseline is 3, but the prose adds semantics beyond the schema: statuses returned, direction MT = sent vs MO = replies received, and the next_page-as-page paging contract. It doesn't restate per-parameter constraints (max lengths, UUID patterns) but meaningfully clarifies the filter vocabulary.

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+resource ('messages') and immediately enumerates the returned fields (delivery status, recipient, sender, text, parts, price), which distinguishes it from the singular smsmode_get_message sibling. The added detail that status.detail names the failure cause shows the tool's output shape rather than restating the title.

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?

Gives real operating context: default window of the last 10 days, how to filter by direction/recipient/ref/channel/campaign, and that the result is paged. It stops short of naming smsmode_get_message as the single-message alternative or stating when filtering is preferable, so the routing is implied rather than explicit.

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