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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false. The description adds real value by disclosing the bulk scope (all texts from one number, not a single message) and the observable effect on the unread counter, but it says nothing about reversibility, whether outbound messages are affected, or what happens when the contact has no messages.

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 with no filler, leading with the action and following with its consequence. Every clause earns its place.

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?

With an output schema present and rich annotations, the description needn't explain return values, and the one parameter is fully documented in the schema. It is complete enough to call correctly; only the no-op case and blast radius details are left implicit.

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% and the single 'contact' parameter is documented down to E.164 formatting and the country-code fallback. The description only echoes the concept ('one number') without adding syntax or edge-case detail, so 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?

States a specific verb (mark as read) and a well-scoped resource (the texts from one number), and the effect clause clarifies the semantic result. It doesn't explicitly name a sibling or rule one out, but no sibling in the list performs an overlapping action, so the purpose is unambiguous.

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?

'so they stop counting as unread' implies the situation that motivates a call, but there is no explicit when-to-use guidance, no prerequisites, and no mention of alternatives such as reading via get_conversation or list_messages. Usage is inferable rather than stated.

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