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

Annotations cover the safety profile (non-readOnly, non-idempotent, non-destructive), and the description adds real behavioral context: the call returns a url and code that must be shown to the user, and the flow is asynchronous so sign_in_status must be polled until active. It omits auth/prerequisite details but goes well beyond the annotations.

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?

Single sentence, front-loaded with the action, then the gating condition, then the follow-up step. Dense but every clause earns its place; the parenthetical is slightly packed but readable.

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 still explains what comes back (url and code), how to surface it, and the required next call, so an agent can complete the flow end to end. Nothing essential is missing.

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 both parameters (agent, purpose) are already documented in the schema. The description adds nothing about parameter format or defaults, which is the expected baseline when 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?

States a specific verb+resource ('Start signing in as your user'), which cleanly separates it from sign_out_everywhere and sign_in_status. It does not explicitly name a sibling it substitutes for, but the verb and resource are 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?

Explicitly states when sign-in is required (hosting invites, joining private ones) and when it is not needed (open invites need no sign-in), and names the follow-up tool. Both the when and the when-not are given.

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