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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so 'Read-only' in the description is redundant. The genuinely additive details are that output is rendered as a visual card and that the default window is 30 days — useful, but not the kind of depth (auth needs, row limits, latency) that would earn a 4 or 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?

Four short sentences, front-loaded with scope and payload before the housekeeping notes. Slight waste in repeating the read-only hint already in annotations, but nothing is padded or buried.

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, the description does the necessary work of naming the return contents (categories with clicks and conversions, per-asset ratings) plus the card rendering note. For an 8-parameter read tool whose parameters are 88% documented, that covers what an agent needs before calling; only sibling disambiguation is missing.

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 88%, so the schema already explains detail, folder, account, date_range, start/end date and language. The description only restates the default period, which the date_range field already documents, and adds no meaning for campaign_id. Baseline 3 applies 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?

The description states a specific scope ('one Performance Max campaign') and enumerates the two payloads returned: search-term categories with clicks and conversions, and Google's asset performance ratings (Best/Good/Low). That is far more informative than the title alone. It does not explicitly differentiate itself from close siblings such as google_ads_pmax_search_themes or google_ads_pmax_assets, which is the only thing keeping it from a 5.

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?

'Use this for one Performance Max campaign' implies the context but names no alternatives and gives no when-not guidance, despite several overlapping siblings in the catalog. The schema's detail enum carries the only real 'use summary vs full' guidance, so the description itself leaves routing to inference.

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