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

With no annotations, the description carries the burden, and it does add valuable traits: zero-persistence, remote streaming, and RCS/WhatsApp targeting. It does not disclose consequences such as send-side effects, costs, fallback behavior, or what happens when neither recipient nor contactsUrl is supplied, so transparency is only partial.

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?

One dense sentence with no filler; the primary single-recipient behavior is front-loaded and the bulk mode is appended as a clearly delimited alternative. Every component adds discriminative value.

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 9-parameter tool with zero required fields and no output schema, the description leaves critical calling context unstated: which parameters must accompany each mode, whether recipient and contactsUrl are mutually exclusive, and what the invocation returns. The omission is significant despite the 100% schema coverage.

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 of 3 applies. The description reinforces the role of contactsUrl ('remote HTTPS CSV/JSONL URL') and urlFormat ('csv/jsonl') but does not clarify parameter combinations or mutual exclusivity beyond what the schema already states.

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 opens with a specific verb and resource ('Sends a rich or text message') and then disambiguates the two invocation modes (single recipient vs bulk stream) plus channels (RCS/WhatsApp). It stands apart from siblings like create_campaign by emphasizing zero-persistence streaming rather than campaign creation.

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 OR between single-recipient and bulk-stream gives an implicit usage choice, and the 'zero-persistence' phrasing hints at when a direct send is appropriate. However, it never names alternatives or states when not to use it versus create_campaign, so the agent must infer routing.

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