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

Annotations already declare readOnly, idempotent and non-destructive, so the bar is lower, and the description still adds real behavior: it blocks for up to 30 seconds, it is cursor-driven via a prior message ID, and it silently yields nothing for paused or pending numbers. What it does not disclose is what the call returns on timeout versus on message arrival.

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?

Three short sentences, front-loaded with the duration limit, then the cursor instruction, then the precondition. No filler or redundancy.

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 three-parameter read-only tool with no output schema, the definition covers the timing bound, the cursor, and a key failure precondition. The notable remaining gap is the return shape on success versus timeout, which with no output schema the description would need to supply.

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 67%, with timeoutSeconds undocumented in the schema; the description covers that gap by indicating a default 30-second wait. It also restates 'after' as the last message ID, but says nothing about the required 'id' beyond what the schema already provides, so it only partially compensates.

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?

States a specific verb and resource ('Wait ... for inbound SMS') with a stated ceiling of 30 seconds, which distinguishes it from list_sms polling. It never names the sibling it replaces, so the differentiation is implicit rather than explicit.

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 'Pass the last message ID as after' line implies a long-poll-after-listing pattern, and the paused/pending caveat tells the agent when the call is futile. There is no explicit statement of when to prefer this over list_sms or wait_for_email, so usage is only implied.

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