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

Annotations indicate readOnlyHint=false, so it's a mutation. The description adds behavioral context: the snippet is 'non-clickable', 'appears beneath an ad', and 'reinforces value props without taking up headline space'. It doesn't contradict annotations. It doesn't detail side effects like account prerequisites, but given the simple create action and annotation coverage, this is sufficient.

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?

The description is well-structured with clear sections (intro, synonyms, keywords, when to use, when not to use, inputs, example). It's longer than strictly necessary but each section adds value for routing and usage. The core purpose is front-loaded, and the rest is organized logically without redundancy.

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 tool with one parameter and no output schema, this description is complete. It covers what the tool does, when to use it, when not to use it, the parameter semantics with examples, and a concrete usage example. Nothing an agent needs to call it correctly 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?

The single parameter callout_text is described in the schema (1-25 characters). The description adds value by providing examples ('Free Shipping', '24/7 Support') and clarifying it's the visible snippet. This goes beyond the schema's minimal description, helping the agent understand what constitutes appropriate 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?

The description clearly states the tool's purpose: 'Add a short non-clickable selling-point snippet (callout) that appears beneath a Google Ads ad'. It uses a specific verb (add/create), identifies the resource (Google Ads callout extension), and provides concrete examples. It distinguishes itself from sibling tools by explicitly mentioning what callouts are not (clickable, lists) and contrasts with sitelinks and structured snippets.

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 description has dedicated 'WHEN TO USE' and 'WHEN NOT TO USE' sections. It gives concrete use cases like 'Add a Free Shipping callout' and explicitly routes to alternative tools for other needs (e.g., 'Want a clickable shortcut... → use create_google_sitelink_extension'). This is explicit, unambiguous guidance with named alternatives.

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