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

Annotations already declare destructiveHint/idempotentHint/openWorldHint, and the description adds genuinely new context: follow permission is required, no subscription is purchased, and an existing invitation may be consumed and will not be restored by unfollowing. The irreversible invitation consumption is exactly the kind of trait 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 tight sentences, front-loaded with the action and trigger before the caveats. The clause 'when the user asks to follow that stream' is mildly redundant with the tool name but not wasteful.

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?

Return values are covered by the output schema, and for a single-param mutation the description supplies the essential missing context – permission requirement, subscription behavior, and irreversible invitation consumption. Little an agent needs to call it correctly is absent.

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?

Only one parameter, and the schema already documents it at 100% coverage ('The id of the stream to follow'). The description adds no format or source detail for id, so this is the baseline 3.

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 (follow a Synoptic stream), clearly distinct from sibling follow_user and from unfollow_stream. It stops short of explicitly naming those siblings as alternatives, but the stream-vs-user scope is 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?

"When the user asks to follow that stream" is an implied trigger rather than a real decision rule, and it doesn't contrast with alternatives like request_stream or unfollow_stream. The invitation note gives a partial hint about when the call has side effects, but no explicit when-not guidance.

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