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

readOnlyHint=true already tells the agent this is a safe read. The description adds genuinely useful context the annotations lack: message bodies may be withheld by FUB for privacy, and it names the backing endpoint. It still says nothing about pagination behavior or ordering, so it does not reach the 4-5 band.

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 tight sentences with the resource and its filter scope front-loaded and no padding. Slightly telegram-style, but every clause carries information.

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 list tool with full schema coverage and no output schema, the description covers the key surprise (bodies may be hidden) and the resource scope. Pagination/ordering behavior and the return shape are unaddressed, but the schema's offset note ('prefer `next`') partially covers that gap.

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%, so all five parameters (limit, offset, personId, toNumber, fromNumber) are already documented in the schema. The description only gestures at 'a person or a phone number' without adding format or semantics beyond that, so the baseline 3 is correct.

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 clear verb+resource (list text messages) and scopes it to 'a person or a phone number', plus the underlying endpoint GET /v1/textMessages. It does not explicitly contrast with siblings like fub_list_calls or fub_log_call, so it falls short of the top band.

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?

There is no when-to-use guidance, no prerequisites, and no mention of alternatives (e.g., fub_list_calls for voice). Usage is only implied by the resource name and the person/phone filter hint, which is the minimum-viable-at-best level.

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