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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, covering the safety profile. The description adds valuable behavioral context: messages are returned oldest first, and when the conversation exceeds the limit, only the most recent messages are returned, with deeper history accessible via sms_list. This goes beyond the annotations without contradicting them.

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?

The description is three sentences, each carrying essential information: purpose, ID discovery, and pagination behavior. It is front-loaded with the primary action and avoids any fluff, making it efficient and easy to parse.

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?

With an output schema defining the return format, annotations covering safety, and the description explaining ordering, pagination, and ID retrieval, nothing essential is missing. The tool is simple (2 parameters, no nested objects) and the description fully equips an agent to use it correctly.

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%, with both parameters described in the schema. The description adds extra semantic value by explaining the behavior of the limit parameter (returns most recent messages when exceeded), which is not in the schema. This enhances understanding of how the limit affects results, though it is a modest addition.

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 verb 'Get' and the resource 'one SMS/MMS conversation with its message history, oldest first.' It distinguishes itself from sms_thread_list (which lists threads) and sms_list (which pages messages) by explicitly mentioning pagination and ordering. This makes the tool's purpose unmistakable.

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?

It provides explicit guidance on how to obtain the required thread ID via sms_thread_list or from any SMS, and explains when to use sms_list for deeper history when the conversation exceeds the limit. This gives clear context for when to use this tool versus its siblings, leaving no ambiguity.

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