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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds useful non-annotation context: the tool is restricted to US postal codes and returns identifiers meant to feed downstream item lookup/search, which is meaningful behavioral scope.

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 well-formed sentence with the key scope constraint (US postal code) and the output purpose front-loaded. No filler or repetition.

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?

An output schema exists, so return values need not be described, and annotations cover the safety profile. For a one-parameter lookup tool the description is nearly complete; only the exclusion/alternative guidance 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 0%, so the description must carry weight. It does clarify that the single required parameter is a US postal code (adding geography/format meaning beyond the bare 'postal_code' name), but provides no syntax, example, or validation detail.

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 ('Find') and resource ('Instacart retailer storefronts') scoped to a US postal code, and clarifies the output's purpose ('identifiers needed for item lookup and search'). This reasonably separates it from siblings like instacart_search or instacart_search_nearby, though it never names those alternatives.

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 phrase 'with the identifiers needed for item lookup and search' implies this is a first step in a workflow, giving implied usage. However, there is no explicit when-to-use guidance and no mention of when to prefer instacart_search or instacart_search_nearby instead.

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