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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds non-obvious behavior: results are limited to the signed-in account, pagination state is preserved, and invitation state is not mutated. It stops short of stating auth prerequisites or page-size behavior, hence a 4 rather than 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, front-loaded with the core purpose, then behavior, then the exclusion. Every sentence earns its place and there is no filler.

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 an output schema present, return values needn't be explained, and the description covers scope, pagination, and the mutation boundary. It does not say what an empty result implies or whether results are ordered, which are minor gaps for a two-parameter read tool.

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% and both parameters (limit, nextToken) are fully documented in the schema, so the description carries no burden here. It only alludes to pagination ('preserves pagination') without adding format or syntax beyond what the schema provides — 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 (List) plus a precisely scoped resource (pending stream invitations addressed to the signed-in account), and names the related sibling follow_stream so an agent can separate listing from consuming. The scope qualifiers ('pending', 'signed-in account') prevent confusion with the many other list_* siblings.

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 the boundary — 'Does not accept or dismiss invitations' — and routes the agent to the correct alternative ('follow_stream can consume an eligible invitation'). That is a clear when-not-use plus a named alternative, which is exactly what the dimension asks for.

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