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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false. The description usefully adds the non-obvious auto-fetch behavior when message_id is omitted and the sender_jid dependency for group chats, which are not fully captured by annotations. It could mention whether read receipts are visible to the other party, but the added operational context is solid.

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 sentences, no filler, with the primary action stated first and conditional behavior following. Every sentence conveys distinct operational 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 full schema coverage, no output schema, and annotations covering safety, the description captures the two non-obvious behaviors an agent needs: auto-fetch on omitted message_id and the sender_jid requirement for groups. It leaves minor gaps like whether read receipts are sent, but is otherwise sufficient for correct invocation.

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 the schema already documents all three parameters thoroughly. The description reinforces the message_id omission behavior and group-chat sender_jid requirement, but largely repeats schema content rather than adding meaning beyond it; 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 description states a specific verb and resource ('Mark a chat as read') that is clearly distinct from siblings like read_chat_history or send_message. It stops short of explicitly naming an alternative, but the purpose 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?

It describes one procedural condition ('Automatically fetches and marks the latest unread message if message_id is not provided') and a parameter dependency for group chats, which implies usage. However, it never says when to choose this over read_chat_history or get_unanswered_chats, so the guidance is only partially implied.

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