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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context beyond annotations: result ordering, conversation grouping logic, and the exact summary fields returned. It doesn't discuss pagination behavior, but that is a minor gap for a read-only list tool.

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 dense sentences with no wasted words. The purpose and sort order are front-loaded, the conversation definition is concise, and the alternative tool is named explicitly. Every sentence earns its place.

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?

Given the rich annotations, fully documented parameters, output schema presence, and clear sibling differentiation, nothing essential is missing. The description covers what the tool returns, how threads are defined, and when to use the complementary tool.

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 three parameters are already documented. The description adds marginal value by restating the agentId filter and clarifying that omitting it shows all accessible agents, but it does not provide additional semantics beyond the schema.

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?

The description states a specific verb and resource ('List SMS/MMS conversations'), defines the unit of conversation, and specifies sorting ('most recently active first'). It also clearly differentiates itself from sms_thread_get by noting it returns summaries rather than full history.

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 description explicitly directs the agent to sms_thread_get for full history, establishing when this summary-level tool is appropriate. It also explains the optional agentId filter and its scope, giving clear context for when to use it versus alternatives.

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