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

Annotations mark readOnlyHint=false, which is otherwise puzzling; the description explains the side effect ("It is marked as read"), states that nothing has been sent, and sets a trust boundary for forwarded third-party content including a prompt-injection warning. That is exactly the context annotations cannot carry.

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 action and identifier source, then the side effect, then the safety note and follow-up path. Every sentence carries distinct, non-redundant information.

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 no output schema, the description implies the shape (header plus body) and states the content is third-party, which is adequate for correct invocation. It could say whether forwarded items can carry attachments (relevant given attachment_list/attachment_read siblings), which is the only real gap.

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?

Only one parameter with 100% schema description coverage that already says "The item_id from list_forwarded"; the description restates the same provenance without adding format or edge-case detail. Baseline 3 applies since the schema does the work.

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?

Opens with a specific verb+resource ("Read one forwarded message in full") and pins the identifier source to the sibling list_forwarded, so an agent can distinguish it from that listing tool without opening a schema. Scope ("one", "in full") 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?

Gives clear context: call it with an item_id obtained from list_forwarded, and when the user wants to act on the content, route to draft_package plus the user's approval. No explicit exclusion versus other read tools (search_messages, get_thread), but the intended usage path is clear.

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