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

readOnlyHint=true already tells the agent this is a safe read, so the description's added value is modest. It contributes the REST endpoint mapping (GET /channels/{channel}/presence) and confirms the real-time semantics, but says nothing about pagination, default limits, or rate limiting.

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 short sentences with the core scope front-loaded and no filler. The endpoint mapping is compact and useful rather than redundant padding.

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 leaves the returned payload shape undescribed (member fields, pagination cursor for large presence sets). For a simple read-only list tool this is a minor gap, but the agent gets no return-value orientation.

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 limit, channel, clientId, and connectionId are all documented in the schema itself. The description adds no parameter meaning beyond what the schema provides, making the baseline 3 appropriate.

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?

States a specific verb (list) and resource (members currently present on a channel), with the parenthetical 'who is online now' clarifying the real-time scope. This implicitly distinguishes it from ably_get_presence_history and ably_get_channel_history, though no sibling is named explicitly.

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?

Usage is implied by 'currently present (who is online now)', which suggests live-state queries over historical ones, but there is no explicit when-to-use guidance, no prerequisites, and no named alternative such as ably_get_presence_history.

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