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

readOnlyHint=true already establishes the safety profile, and the description adds genuinely useful behavior: the newest-first default ordering, the 7-day implicit window that silently truncates results, and the two cursor conventions. These are non-obvious traits an agent could not infer from the annotations.

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?

Four sentences, front-loaded with what the tool returns, then constraints, then paging, then the REST mapping. Reasonably tight, though the cursor explanation duplicates what the schema already says for before_id/after_id.

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 10-parameter read-only list with no output schema, the description covers ordering, the window constraint, and paging well enough to call correctly. It does not describe the returned message shape or pagination termination (how the agent knows it has reached the end), which are the remaining gaps.

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 ten parameters are already documented in the schema, including enum meanings and paging cursors. The description largely restates the before_id/after_id mechanics rather than adding format or constraint detail beyond the schema, so the baseline 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?

Specific verb+resource with scope: 'List sent (SENT) and received (RECEIVED) SMS messages, newest first by default', plus the underlying REST endpoint. It does not, however, differentiate itself from the sibling bulksms_list_replies, which an agent could reasonably confuse with the RECEIVED half of this listing.

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 operational context: the 7-day default window and the condition that lifts it (submission_date_from), plus which paging cursor to use under each sort_order. It stops short of stating when to prefer this tool over bulksms_list_replies or bulksms_get_message.

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