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

Annotations only mark it as non-read-only; the description adds meaningful behavior: stock is either set absolutely or adjusted relatively, and the resulting stock must remain >= reserved. This is the key invariant the agent needs, though error behavior is not described.

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 with no filler. The primary action is first, the parameter-selection guidance is second, and the invariant is stated last. Every sentence 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?

For a 3-parameter, no-output-schema mutation, the description plus 100% schema coverage cover required inputs and the main constraint. It is slightly incomplete because it does not indicate what a successful response contains or how a violation of the reserved-stock invariant is reported.

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 coverage is 100%, so the schema already defines product_id, stock as absolute, and delta as a signed adjustment. The description repeats 'absolute value'/'relative change' and the reserved constraint, adding little beyond what the schema provides. Baseline 3 is appropriate.

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 uses a specific verb and resource: 'Update a listing's stock count'. It also states the two update modes (absolute stock vs delta), which distinguishes it from the broad seller_update_listing sibling. The purpose is unmistakable.

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 clearly explains when to pass stock vs delta, and the reserved-stock constraint gives context for valid calls. However, it never mentions seller_update_listing or states when to prefer this tool over the general listing-update alternative, so tool-selection guidance is only implied.

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