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

Annotations only declare destructiveHint=true; the description adds the cost model (one credit per 160 GSM characters per recipient, unicode costs more), irreversibility ('Cannot be undone'), and a hard recipient cap of 10. This is exactly the behavioral context an agent needs before a money-spending, destructive action, and it is consistent with the annotation.

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?

Front-loaded with the two highest-severity facts ('WRITE, SPENDS MONEY'), then constraints, then the precondition. Dense but every clause carries operative information; nothing is padding.

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?

Covers cost, limits, irreversibility and preconditions, which is most of what is needed for a mutation tool with only a destructiveHint annotation. It does not indicate what the call returns (no message ID / response shape explained), a minor gap given no output schema exists.

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%, so the baseline is 3. The description goes beyond the schema by tying message length and the `unicode` flag to credit consumption, which lets an agent reason about cost implications of parameter choices rather than just syntax.

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 ('sends a REAL SMS to real phones') with the scope of the operation made explicit. It is unmistakably the only write/send tool among a sibling set of read/report/contact-management tools, so an agent can route to it without ambiguity.

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 a strong precondition — 'Only call after the user confirmed the exact text, sender and numbers' — and rules out unsupported workflows ('no groups, templates, scheduling or repeats'). It does not name an alternative sibling, but none exists for this operation, so the guidance is effectively complete for routing.

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