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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is known; the description adds the crucial replace-not-increment semantics ("the number given replaces the stored one") and states it returns previous and new quantity. It does not mention the stale-edit refusal path or permission requirements, though the schema covers the former.

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?

Three tight sentences, front-loaded with the usage trigger, then behavior, then the exclusion. No filler or redundant restatement of the title.

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 mutating, optimistic-concurrency tool, the description plus the 100%-covered schema and output schema give an agent enough to call it correctly. Only minor gaps remain, such as no mention of what happens when the edit-time check fails or of permission requirements.

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% and an output schema exists, so the baseline applies. The description's replace-semantics sentence largely restates the quantity field's own schema description rather than adding new meaning about inventoryItemId or expectedLastEditTime.

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 and resource (correct/update how much of a supply is in stock) and includes an explicit negative scope ("Not for adding a new stock item"), which separates it from the read-only list_inventory_items sibling. An agent can identify the operation without opening the schema.

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?

Gives concrete triggering situations (after counting towels, receiving a delivery) and an explicit exclusion (not for creating new stock items). Both the when and the when-not are present, leaving little to inference.

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