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

Adds substantial behavior beyond the annotations: idempotency ('Already-present membership stays present'), input validation outcomes ('Wrong kinds or cross-Account IDs are refused'), an access requirement, an explicit non-effect ('launches no Scan'), and a 1–100 ID cap. This is exactly the kind of context annotations (readOnlyHint=false, destructiveHint=false) cannot convey.

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-loads the purpose, then layers semantics, constraints, and prerequisites in a logical order. Dense with clauses, but nearly every clause carries distinct decision-relevant information; only the double back-reference to list_clients/list_sites_and_topics overlaps with the schema descriptions.

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?

An output schema exists, so return values need no explanation. Combined with annotations, the description covers access requirements, idempotency, validation failures, ID limits, related tooling for ID resolution and verification, and the non-effect on Scans.

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 75%, and the description compensates for the remainder by explaining the semantic model: Client membership implicitly includes all current/future brand Sites, topics need explicit attachment, direct Site/topic attachments may coexist with Client membership, and the 1–100 limit applies to distinct IDs across all three arrays combined — a constraint not expressed in the schema.

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 (Add) plus the exact resources (Client, Site, topic membership) and the target object (an agency Account Portfolio). It is immediately distinguishable from the sibling remove_members_from_portfolio and from create_portfolio.

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?

Gives strong operational context: prerequisite resolution helpers (list_clients, list_sites_and_topics), a verification tool (get_portfolio before/after), and a negative statement ('launches no Scan'). It does not explicitly contrast with remove_members_from_portfolio or say when a separate call would be preferred, so it stops short of full when/when-not coverage.

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