Update X Pixel

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

Annotations already indicate this is a write operation (readOnlyHint=false) and has open-world effects (openWorldHint=true). The description adds a key behavioral context: 'Only fields the user named,' which clarifies that unspecified fields won't be changed. However, it does not discuss side effects implied by openWorldHint, permissions, or idempotency.

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, front-loaded sentence conveys the core purpose, the fields it affects, and the partial-update behavior. There is zero waste, and key information is placed early.

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?

The tool is a partial update with openWorldHint and no output schema, so the description should cover side effects and the response. It clarifies the partial-update semantics but does not mention what happens with validation failures, whether the operation is reversible, or what is returned. Given the openWorldHint, one would expect more detail about potential external impacts.

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 only 17% (only account_id has a description). The description groups parameters into 'name, windows, or retargeting,' which helps map to the actual fields (name, click_window, view_through_window, retargeting_enabled), but it does not elaborate on allowed values or types beyond what the schema already illustrates. It adds some meaning but does not fully compensate for the low schema coverage.

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 verb ('Partial update') and a clear resource ('web event tag') plus which fields can be updated ('name, windows, or retargeting'). This distinguishes it from other update tools for audiences, campaigns, and ad groups, making it unambiguous.

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 is clear that this tool modifies an existing pixel, but it does not provide explicit when-to-use or when-not-to-use guidance, nor does it mention alternatives like creating a pixel or deleting it. It lacks explicit exclusion criteria relative to sibling update tools.

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