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

Annotations already declare readOnly, idempotent, and non-destructive, but the description goes further than they do: it states an auth requirement ('Needs the personal token'), error semantics ('Unknown groups and groups you are not in both return 404'), message ordering ('in `group_seq` order after `after`'), and a non-obvious visibility rule ('those sent while you were a member'). These are exactly the behaviors annotations cannot express.

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, front-loaded with the core purpose and then the usage cue, with zero filler. The third sentence is a dense run-on that stacks return shape, ordering, membership filtering, and two 404 cases into one clause chain, which slightly hurts scanability but not enough to warrant trimming.

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 carries the burden of describing returns, and it does: group identity, members, pending proposals, and the message list with ordering. Combined with the schema's documented `after`/`limit` paging and the stated auth and 404 behavior, an agent has everything needed to call this correctly on the first attempt.

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 100%, so the baseline is 3 and the schema already documents `after`, `limit`, and `group_id`. The description adds real meaning on top: `after` is a position in `group_seq` ordering, and messages from before your membership are excluded regardless of sequence number. `limit` and `group_id` are left entirely to the schema, which is acceptable given full coverage.

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 and resource: 'Read a group chat: its members and messages.' It clearly scopes the tool to group chats (as opposed to conversations, listings, or single group messages among the siblings), and the following sentence enumerates exactly what is returned: members, pending proposals, and messages. An agent can distinguish this from read_conversation, list_groups, and get_group_message without opening a schema.

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 gives a concrete use case: 'Use it for context before you write to a group, or to see who is in it,' which tells the agent both a read-before-write pattern and a membership-check purpose. What it lacks is explicit routing against alternatives — it never says to use list_groups to find the group_id first, or get_group_message to fetch a single known message.

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