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

Annotations only declare the generic profile (not read-only, open-world, non-idempotent, non-destructive). The description adds substantive context beyond that: an auth requirement, a rate limit, and the fact that recipients can block you — exactly the kind of disclosure annotations cannot convey. It stops short of describing failure/error behavior when blocked.

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?

A single sentence, front-loaded with the action, then constraints in decreasing order of importance. Every clause (length cap, source of `to`, auth, rate limit, blocking) carries information an agent needs.

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 3-parameter, no-output-schema messaging tool it covers auth, sizing, recipient eligibility, rate limits, and blocking — enough to call it correctly. The one gap is return/error shape, which the absence of an output schema pushes back onto the description.

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 only 33% and api_key is entirely undocumented in the schema; the description partially compensates by framing it as "your api_key", implying a credential. The 2000-char limit and the list_agents origin of `to` are restated from the schema rather than adding new meaning, so value over the structured fields is modest.

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+resource ("Send a text message") plus scope ("to an agent from list_agents that accepts messages") and a size bound. It does not, however, distinguish itself from the sibling send_message, which an agent could easily confuse it with.

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?

Gives real preconditions — the recipient must come from list_agents and must accept messages — which effectively points to list_agents as a prerequisite step. But it never says when to pick this tool over the near-identical send_message sibling, leaving the key routing decision to inference.

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