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

Annotations already cover read-only, idempotency, and non-destructive behavior, so the bar for adding behavioral context is lower. The description adds useful context about ordering ('most recent first') and the scope ('authenticated business'), but it does not go into pagination or return details. This is acceptable given the output schema and 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?

Two sentences with no wasted words. The key action and scope are front-loaded, and the API mirror line provides a useful reference without padding. 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?

For a simple read-only list tool with one optional parameter and an output schema, the description is nearly complete. It specifies the resource, scope, and ordering, and the complexity is low, so little more is required. A slight improvement would be to mention that this returns threads, not individual messages, but that is already implied by 'threads' and the sibling list.

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% for the single optional limit parameter, which is fully documented with min/max and default. The description adds nothing beyond the schema, so a baseline of 3 is appropriate.

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 clearly states the action (list), the resource (SMS conversation threads), and the scope (authenticated business, most recent first). It also distinguishes itself from siblings like list_sms_messages and get_conversation by specifying 'threads' and 'counterparty timeline metadata', and maps to a precise API endpoint.

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 provides no guidance on when to use this tool versus alternatives such as get_conversation or list_sms_messages. It simply states what the tool does without any conditions, exclusions, or references to sibling tools, leaving the agent to infer selection criteria.

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