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

Annotations already declare readOnlyHint=true and destructiveHint=false, covering the safety profile. The description adds meaningful context by specifying that the response includes threadId for joining the conversation, which helps the agent understand expected output. No contradictions or hidden behaviors are suggested.

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 concise sentences with no fluff. The first sentence front-loads the key action and a valuable output detail, and the second sentence cleanly points to the sibling tool for the broader use case.

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?

The definition is complete for a simple single-fetch tool: one parameter is fully documented in the schema, an output schema exists to describe returns, annotations cover safety, and the sibling tool distinction is clear. Nothing necessary for correct invocation is missing.

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 the parameter 'id' is already documented as 'SMS message ID.' The description does not add format or source details beyond the schema, so it meets but does not exceed the baseline.

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 the specific verb 'Fetch' and resource 'full detail for a single SMS by ID', and distinguishes it from sms_list by noting that sms_list is for browsing multiple messages. Including the threadId detail further sharpens the purpose.

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 tells the agent when to use this tool versus sms_list: 'Use sms_list to browse multiple SMS messages.' This directly routes to the appropriate sibling for the alternative use case, leaving no ambiguity about scope.

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