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

Annotations already cover readOnlyHint and destructiveHint, and the description adds the key no-side-effect behavior by saying 'Preview only'. It also discloses the output shape at a conceptual level (region/state/DMA list or postcode list), going beyond the structured annotation fields.

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 sentences with no filler: the transformation, output types, examples, and preview/apply relationship are all packed in. The most important scoping information ('Preview only') is placed before the alternative.

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 read-only preview tool with two well-documented parameters, the description covers what it does, what it returns conceptually, and what to do next. It could specify the exact return schema, but no output schema is present and the conceptual output description is sufficient for selecting and 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 baseline is 3. The description adds value by giving concrete examples of acceptable locations_text values ('Texas and Florida', 'Greater London', 'zip codes starting 902'), which clarifies the free-text format beyond the schema's brief description.

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 uses a specific verb and resource: 'Turn a free-text location description ... into structured targeting', and clarifies the result forms ('region/state/DMA selection or a postcode list'). It distinguishes itself from siblings by explicitly flagging 'Preview only' and naming set_location_targeting as the actual application step.

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 instruction 'Preview only — apply with set_location_targeting' gives an explicit alternative and tells the agent when this tool is appropriate. This is analogous to the high-calibration example that named its sibling and the condition for using it.

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