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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safe, local, repeatable behavior is covered. The description adds the useful workflow hint about piping output into generate_qr_code, but says nothing about output format specifics or how SMS clients handle the payload. With annotations doing the safety work, a 3 is appropriate.

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: the first names the resource and its formats, the second gives the next-step instruction. Nothing is redundant and the purpose is front-loaded.

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 small, pure 3-parameter formatter with full schema coverage and no output schema, the definition covers purpose and downstream usage adequately. A brief note on which format to prefer in ambiguous scanner cases would complete it.

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%, with phone format, the sms/smsto enum meaning, and message maxLength all documented in the schema itself. The description adds no syntax or format detail beyond that, so the baseline 3 applies.

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?

Specific verb and resource: builds an SMS payload in sms:/RFC 5724 or SMSTO: form. It clearly differs from siblings like qr_payload_wifi or qr_payload_email, which build payloads for other content types, and it explicitly names generate_qr_code as the consumer.

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 states the downstream step clearly ('Pass the result as `data` to generate_qr_code'), which tells the agent when to use it and how it fits into a QR creation flow. It doesn't explicitly say when NOT to use it versus the other qr_payload_* siblings, but the SMS-specific framing makes the boundary obvious.

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