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

The readOnlyHint annotation already establishes safety, and the description adds useful context beyond it: the exact scope of the response (account, user, capabilities) and the underlying endpoint GET /me, which signals it targets the control plane rather than a data plane. It omits auth/permission prerequisites, keeping it short of a 5.

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, each earning its place: what it returns, when to use it, and the backing API call. The purpose is front-loaded with no redundancy.

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 return-value burden and does so at a summary level (account, user, capabilities) rather than describing the response shape. That is adequate for a trivial identity probe, though slightly more on the returned fields would make it airtight.

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?

The tool takes zero parameters, so the baseline of 4 applies. Nothing in the schema needs compensating for, and the description correctly avoids inventing inputs.

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 (Return) and resource (details about the configured control token), enumerating the returned data: the account, the user, and capabilities. This clearly distinguishes it from data-plane siblings like ably_get_channel_details or ably_list_apps.

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?

"Good first call to confirm control-plane access" gives the agent a concrete situation in which to reach for this tool. It doesn't name an alternative or state exclusions, but for a unique zero-param identity probe no real alternative exists.

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