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

Annotations already carry the operational profile (readOnlyHint, idempotentHint, openWorldHint), so the bar is lower. The description adds genuinely useful behavior beyond that: output is ordered with the hero photo first, and size=full expands each photo to every size Zillow serves. This is meaningful context, though edge cases like empty galleries are not covered. No contradiction with annotations.

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, roughly 30 words, with the core purpose and output shape front-loaded. The second sentence earns its place by explaining the size=full expansion behavior. There is no filler or redundant phrasing.

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?

This is a simple tool — one required parameter, read-only, idempotent, open-world — and the description covers the response shape while the schema documents all three parameters, including expand's compact/full tradeoff. No critical information for making a correct call 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%, so the baseline is 3. The description's size=full sentence essentially restates the schema's own size description ('full to add every image size Zillow serves'), so it adds no new semantic information beyond what the schema already provides.

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 identifies the resource precisely — a home's photo gallery — and specifies the output structure (one URL per photo, in order, hero first). This scope clearly distinguishes it from siblings like zillow_floor_plans, zillow_price_history, and zillow_market_stats. The missing explicit verb ('returns') is a minor style issue that doesn't hurt clarity.

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 states what the tool returns but never articulates when to choose it over alternatives. Usage is only implied by the tool name and the phrase 'photo gallery for a home'; no sibling is named and no conditions, exclusions, or decision rules are given.

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