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

The description goes beyond annotations by disclosing the deep-merge behavior of the system object and warns that arrays are replaced whole. This is a critical non-obvious behavior that could otherwise lead to accidental data loss. The description does not contradict any 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 compact and front-loaded: it states the action, then the prerequisite, then the crucial deep-merge caveat with examples. Every sentence earns its place, and the example payloads communicate a lot in few words.

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 partial-update tool with a nested schema and no output schema, the description covers the key workflow precondition and the most important behavioral trap. The rest of the details are well covered by the schema, so the agent has enough information to invoke the tool 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?

Schema coverage is 100%, so the baseline is 3. The description adds meaningful value by explaining how to use the system parameter: pass only changed fields, with concrete examples like {"quantity": 3} and {"uses": {"value": 0}}. It also reinforces that itemId comes from item-list, adding practical semantics beyond the schema labels.

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 states a specific verb and resource: 'Update an item in actor's inventory.' It clearly separates this from item-create, item-delete, item-list, and world-item-update by scoping the update to an actor's inventory. The wording leaves no doubt about what the tool does.

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 explicitly instructs the agent to call item-list FIRST to obtain the itemId, which is a concrete prerequisite and workflow guideline. It does not explicitly discuss when not to use this tool or compare it with item-update vs world-item-update, but the actor inventory scoping provides enough contextual guidance.

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