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

Annotations give readOnlyHint=false, openWorldHint=false and destructiveHint=false, but the description adds context the annotations cannot: an unacked message is re-offered after 10 minutes, an empty list means nothing new, and returned messages should be treated as user instructions. The readOnlyHint=false is consistent with delivery/ack semantics that mutate state rather than contradicting the description.

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?

Four sentences, each carrying distinct information: what it fetches, when to call, how to ack, and the re-offer/empty-list semantics. The core action is front-loaded and nothing is redundant.

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?

There is no output schema, and the description compensates by explaining return semantics ('an empty list means nothing new') and the delivery/ack lifecycle. The only minor gap is that it does not describe the shape of an individual message object, but the essential contract is complete.

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%, so both limit and bot_name are already fully documented in the schema, including defaults, maximums and the addressing behavior of bot_name. The description adds no syntax or format detail beyond that, so the 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 and resource ('Fetch new messages the user sent you from Heard') and immediately scopes it ('Returns only messages for you'). It is clearly distinguishable from heard_inbox_ack and heard_report, both of which it either names or alludes to through the bot_name parameter.

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?

Explicitly prescribes when to call ('at the start of every task, between steps, and before you finish') and names the follow-up alternative with its condition ('After you act on a message... call heard_inbox_ack with its id'). This is the strongest possible routing guidance for an agent.

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