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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds real behavioral nuance beyond that: delivery is broken out per channel with times, and 'read' is defined as an explicit mark_read watermark rather than inferred activity — that tells an agent why a recipient may look unread despite having seen the message. It still says nothing about permissions, empty/partial results, or errors for an unknown seq.

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 sentences, front-loaded with the question the tool answers, then the payload breakdown, then the invocation requirement. No filler and no repetition of the title or annotations.

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 shape need not be explained, and the two required parameters are both named. The gap is operational: an agent is not told where conv_key and seq come from (list_messages/list_conversations are siblings) or what happens when the message or recipient set is missing, which matters for a lookup keyed on opaque identifiers.

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 0% for both required parameters, so the description carries the burden. It does name both ('conversation key', 'message seq') and ties them to the lookup, which is the minimum an agent needs to invoke correctly. However it adds no format, provenance (e.g. where to obtain conv_key/seq), or edge-case semantics for either parameter.

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 states a specific resource and verb implicitly through 'Per recipient: sent, delivered ... and read' — it is clearly a delivery/read receipt lookup for one message. It is distinguishable from get_watermark and mark_read (which set state) and from get_poke_receipts (a different receipt family). It stops short of naming a sibling it is not, so it is clear but not fully differentiated.

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 opening question 'Did my message arrive?' frames the use case, and 'Pass the conversation key and the message seq' implies this is a per-message lookup requiring a prior send. There is no explicit when-not guidance, no mention of what to use for conversation-level or workspace-level delivery status, and no prerequisites stated.

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