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

Annotations already indicate readOnly, idempotent, and non-destructive. The description adds valuable context about live backend data (FoV, distortion, stock via Shopify) that the model cannot derive on its own. It also warns against shortcut assumptions, enhancing transparency beyond the 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?

The description is highly repetitive, containing near-identical sentences multiple times (e.g., the 'Use this tool for' and 'Do not use' phrases appear twice, and the sensor alias list is duplicated). This verbosity obscures the core message and could be streamlined to a single clear statement.

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?

Given the complexity of 18 parameters and multiple aliases, the description covers purpose, usage, parameter alternatives, and even output labelling (CUSTOM-<w>x<h>). It does not explain return values in depth but the absence of an output schema means the description carries more weight; it is sufficiently complete for an agent to invoke correctly.

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?

While the schema provides individual parameter descriptions, the description ties them together by explaining alternative ways to specify a custom sensor (pixels × pitch vs. mm dimensions) and mentions the 'CUSTOM-<w>x<h>' output label. This adds meaningful semantic guidance beyond the raw schema, though the schema already covers most fields.

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 clearly states the tool's purpose: to find and rank Commonlands lenses for a sensor, FOV, working distance, mount, or 'lens for' request. It explicitly lists use cases (FOV, sensor part numbers) and distinguishes from siblings by directing away from naive rectilinear fallback and focal-length-only math when a Commonlands route exists.

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?

It provides explicit 'Use this tool for...' guidance and 'Do not use...' exclusions, including concrete examples like AR0234, IMX290, IMX477 and workflows such as M12/C-mount matching. This clearly differentiates when this tool should be selected over alternatives like search_catalog or recommend_lenses_for_application.

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