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

Annotations already declare readOnlyHint and non-destructive, so the safety profile is covered. The description adds behavior the annotations can't: it discloses the not-connected case and that the response then carries a grant_url the user must open to add Merchant Center — genuinely useful operational context an agent needs to handle the empty/error path.

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 what it lists, then the downstream use, then the edge case. No repetition of the title or annotations; every sentence carries distinct information.

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 and no params, the description carries the return-value burden and does address the notable branch (grant_url when unconnected). It doesn't characterize the shape of the returned account objects (id, name, sub-account nesting), which would be the last missing piece.

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?

Zero parameters, so the baseline is 4. The description still adds value by explaining where the account_id consumed by sibling tools comes from, tying this no-arg call into the broader workflow.

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 ('Lists') and resource ('Google Merchant Center accounts'), plus the scope detail that sub-accounts of advanced/multi-client accounts are included. That scope detail plus the Merchant Center qualifier is enough to separate it from sibling list_accounts/account_overview without opening a schema.

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 a clear downstream directive: 'Use an account_id from here in the other Merchant Center tools,' which establishes this as the entry point for the merchant_* family. It stops short of naming an explicit alternative or a when-not-to-use condition, so it's clear context rather than full routing guidance.

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