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

Annotations already declare readOnly, idempotent, non-destructive, and open-world behavior, so the safety profile is covered. The description's genuine addition is the plan gate: a refusal with `feature_not_available` that no retry will fix, which prevents wasted retries. It adds nothing about rate limits, permissions, or result shape, so it is a solid but not rich supplement.

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?

Three short paragraphs: what it returns, when it matters, and what blocks it. The most decision-relevant facts (per-recipient view, plan gate) are front-loaded with no filler.

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?

An output schema exists, so return-value explanation is unnecessary, and parameters are fully covered by the schema. The description supplies the one non-obvious operational fact (plan-gated, non-retryable failure). Only the explicit sibling routing is missing.

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%, and both parameters (message_id, number_alias) are fully documented in the schema with format hints and a pointer to list_numbers. The description adds no parameter-level meaning, 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?

The opening sentence states a specific verb and resource: per-recipient receipt and read status for a message. The second paragraph implicitly separates it from get_message_status by explaining that the message-level single status cannot express partial reads in groups, though it never names that sibling directly.

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?

It gives clear usage context (group messages where per-member read state matters) and a hard prerequisite (a plan with read receipts). It stops short of an explicit 'use X instead when...' routing statement against get_message_status or get_message_responses.

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