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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so safety is covered. The description adds real context beyond them: the result is hierarchical (manager accounts with their direct client accounts) and includes the login_customer_id needed for downstream calls. It omits pagination/rate-limit and auth-scope behavior.

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?

A single sentence with the core purpose front-loaded and no filler. The closing clause ('with the login_customer_id to use for them') is slightly tangled but carries important 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?

For a zero-parameter discovery tool with no output schema, the description should say more about what each account entry contains (id vs name, currency, timezone, manager flag) or confirm it takes no arguments. It covers the shape of the hierarchy but leaves the per-account fields undescribed.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The description's note about login_customer_id is about a returned value, not an input.

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 ('Lists the Google Ads accounts') and adds useful scope: accounts the signed-in user can open plus client accounts under each manager account. It is clearly distinct from siblings like account_overview, though it never names them explicitly.

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?

Usage is implied rather than stated: mentioning the 'login_customer_id to use for them' hints that this is the entry point for discovering accounts before calling other tools, but there is no explicit 'call this first' or when-not guidance, and no alternative sibling is named.

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