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

Annotations only cover readOnlyHint and openWorldHint; the description adds a genuinely useful behavioral fact not in the annotations — that the call is 'credential-free' — plus the aggregate scope ('across every retailer ... at once'). It doesn't discuss result caps or pagination, but the auth disclosure is real added value beyond the structured 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?

A single sentence that front-loads the resource and return type, then the scope, then the differentiator. No filler, and the most decision-relevant comparison is kept short and parenthetical.

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 present, return values need no explanation, and annotations already carry the safety profile. Purpose, scope, auth posture, and the sibling alternative are all covered; only secondary details like result limits are absent, which is minor for a two-parameter read 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%, with 'q' and 'postal_code' fully documented in the schema, so the baseline is 3. The description restates their roles ('for a keyword', 'serving a postal code') without adding format, syntax, or validity constraints beyond what the schema already supplies.

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?

It names a specific verb+resource ('Instacart search-term autosuggestions') plus the exact scope ('for a keyword across every retailer serving a postal code'), and explicitly positions itself against the sibling instacart_search. An agent can tell immediately that this returns suggestions rather than products or stores, despite the 'search_nearby' name.

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 parenthetical 'unlike instacart_search's single-store lookup' tells the agent which alternative to pick when it wants all retailers at a ZIP rather than one store. It stops short of stating exclusions or when-not-to-use (e.g., when you already know the retailer and want actual items), so it's clear context rather than a full routing rule.

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