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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false, and openWorldHint=false, so the mutation profile is covered. The description adds the one-line return shape (created asset resource name) but says nothing about duplicate-creation behavior despite idempotentHint=false, nor about permissions or quota implications.

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 purpose statement is front-loaded in the first sentence and the Args/Returns structure is easy to scan. Slight redundancy with the return-value sentence given an output schema exists, but no filler.

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 4-param mutation tool with annotations and an output schema, the definition covers identity, field formats, enum values, and default. The remaining gap is operational behavior (duplicates, permission requirements) rather than anything that would block a correct call.

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 coverage is 0%, yet the description documents all four parameters with real added value: customer_id must be numbers only with no hyphens, country_code is two-letter with examples, and call_conversion_reporting_state enumerates the three valid values plus the DISABLED default — none of which the schema itself carries. Only phone_number ("The phone number string") is left without format guidance such as E.164.

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 ("Creates a call asset") and clarifies its role — a phone number attached to an ad — which differentiates it from the many sibling create_*_asset tools. It also notes the asset must then be linked to a campaign or ad group, hinting at the follow-up tool, though it does not name link_asset_to_campaign 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 only implied: the mention that the asset "can be linked to campaigns or ad groups" suggests creating first then linking, but no sibling is named and no prerequisite (e.g., an existing call conversion action for the USE_RESOURCE_LEVEL state) or exclusion is given.

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