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

Annotations already establish that this is a non-read, non-destructive write operation, and the description does not contradict them. It adds one meaningful behavior – position, width, and height are auto-defaulted rather than configurable – but it doesn't disclose the resulting defaults, possible duplication behavior, or any side effects.

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?

Two short sentences with no filler; the primary action is front-loaded and the defaults note earns its place by explaining an otherwise missing aspect of the API. It is appropriately sized for the tool's low complexity.

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 an output schema, complete parameter descriptions, and annotations, the description covers what an agent needs to select and call the tool. The only minor gap is the vagueness of 'sensible defaults' – an agent cannot predict or communicate the exact resulting position and size – but this is not critical for invoking the tool.

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 the schema already defines each parameter. The description's only contribution is the 'sensible defaults' note, which explains why position, width, and height are absent from the schema but does not add semantics to link, text, page_id, client_id, or source_id.

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 an explicit action ('Add') with a specific resource ('button widget') and target ('a page'). The resource name differentiates it from siblings such as add_text_widget and add_image_widget, and the defaults sentence clarifies scope without ambiguity.

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 implies when to use it – when the user wants a button widget placed on a page – but it does not explicitly address alternatives or exclusions. There is no mention of when to prefer another add_*_widget sibling or update_button_widget, so the guidance relies on inference from the tool name.

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