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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds a genuine behavioral scoping fact beyond the annotations: only *active public* promotions are returned, so the agent knows expired or non-public offers are excluded. It says nothing about pagination or rate limits, but with an output schema covering the return shape the remaining gap is small.

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, no filler. The purpose and scope constraint are front-loaded, and the routing guidance follows immediately after. Every clause earns its place.

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?

All three parameters are schema-documented, the annotations carry the safety profile, and an output schema exists so return values need not be explained. Purpose, scope, and sibling routing are all present — nothing an agent needs to select and invoke the tool 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?

Schema description coverage is 100% and all three required parameters (restaurant_id, latitude, longitude) are documented in the schema, so the baseline is 3. The description adds no parameter-level meaning such as why both a restaurant_id and diner coordinates are needed.

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?

Specific verb (Fetch) plus a precisely scoped resource (active public promotions for a Grubhub restaurant) and an enumeration of payload contents (offer terms and savings). It also distinguishes itself from the menu sibling in the same breath, so an agent can separate the two without opening either schema.

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 second sentence gives an explicit when-to-use (comparing available deals) and names the alternative (the restaurant's menu tool) along with the condition that selects it (purchasable items). Nothing about routing between the two tools is left to inference.

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