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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered structurally; the description's useful addition is the parenthetical listing which fields come back. It does not mention behavior on a missing/invalid ad id, cross-account resolution, or rate limits. With annotations carrying the safety load, a 3 is appropriate.

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, front-loaded with the verb and resource, with the field list appended as a compact clause. Nothing is redundant or padded.

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 simple read-only getter with full annotation coverage and full schema coverage, this is close to sufficient, and the field list partly compensates for the absence of an output schema. It stops short of describing not-found behavior or the account-resolution fallback beyond what the schema notes.

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%, so both ad_id and the optional customer_id (with its default-to-connected-account note) are already documented in the schema. The description adds only the confirmation that the lookup is keyed on id, which is the baseline expectation when the schema does the heavy lifting.

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 ('Get one Google Ads ad by id') and enumerates the fields returned, so it is clearly a single-record fetch rather than a list. It does not explicitly name google_ads_list_ads or google_ads_query as the alternative, so sibling differentiation is only implied by 'one ... by id'.

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?

The 'by id' framing implies you need a known ad id, which implicitly contrasts against list/search tools, but no when-to-use or when-not-to-use guidance is stated. Nothing tells the agent what to do if it only has a campaign or ad group name.

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