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

Goes well beyond the annotations: it discloses that the call creates a session or links the supplied one, returns the session and the page's watch link, that a new session is started on every call without a code, and that nothing is deleted. The non-idempotency hinted by idempotentHint=false is spelled out in concrete terms.

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?

Front-loaded with the action and its payoff, and every clause carries information. Slightly dense, and 'nothing is deleted' partially duplicates destructiveHint=false, but it costs little and reassures on a mutation.

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 one optional parameter, no output schema and only sparse annotations, the description covers the action, the gating condition, the side effects, and the return values (session plus watch link). An agent has enough to call it correctly and to know what comes back.

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% and the single property already documents the 64-hex session code and that omitting it starts a new session. The description reinforces the omit-behavior ('a new session starts each time it is called without a code') but adds no format or validation detail beyond the schema, so 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?

States a specific verb and resource ('Connect to the HenryKnows page the person is watching') plus the concrete outcome ('get the session for share_to_page'), which also positions it relative to the share_to_page sibling. The parenthetical 'its light turns green' makes the effect observable.

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 gates usage: 'Only for people who gave you a session code or asked to follow along on a page.' That is a clear when-to-use and an implicit when-not-to-use. It stops short of naming an alternative tool (e.g. ask_henry) for the case where no page is involved, so it is not a full 5.

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