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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world scope, so the safety profile is covered. The description adds two useful boundary statements — the receipt is immutable and does not backfill acknowledged context or prove comprehension — which correctly prevent over-reading the result, but reveals nothing about size limits, pagination, or error behavior.

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?

Two compact sentences with no filler, and the scope limitation is placed immediately after the purpose. The jargon density ('answer-context receipt', 'current comparison') costs a little clarity but 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, so the description carries the burden of describing the return value, and 'immutable answer-context receipt and current comparison' only gestures at its shape without field-level detail. Safety is fully covered by annotations and the negative constraints are stated, but an agent still does not know what it will receive or how to interpret 'comparison'.

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 50%: room_id is documented in-schema (OAuth-authorized room), while 'number' has only a numeric range. The description compensates partially by clarifying that 'number' is a room-local message number, which is real added meaning. It still leaves ambiguity about ordering, gaps, or what happens when the number has no receipt.

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 verb 'Returns' and object 'answer-context receipt' identify a read operation, but 'answer-context receipt' and 'current comparison' are domain jargon that an agent cannot resolve without prior knowledge. It is distinguishable from siblings like read_message or read_around only by the phrase 'by room-local message number', which is weak differentiation.

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 description states only what the tool does NOT do ('does not backfill acknowledged context or prove comprehension'), with no positive guidance on when an agent should call this instead of read_message, read_around, or read_attachment. No prerequisites, no trigger conditions, no named alternative.

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