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

Beyond the annotations, the description discloses non-obvious behavior: folder is tri-state with omit/string/null semantics, clearFolder overrides folder, and system is deep-merged by Foundry allowing surgical partial updates. This significantly exceeds what readOnlyHint:false alone conveys.

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 dense sentences with no filler. The purpose is front-loaded, and each nuance (folder, clearFolder, system merge) earns its place. It is thorough without being bloated.

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 a 6-parameter update tool with nested objects, the description covers all tricky semantics: folder tri-state, clearFolder override, and deep-merge of system. The only minor gaps are unspecified return behavior and no mention of prerequisites/permissions, but no output schema exists and these are not critical to correct invocation.

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?

Although the schema already covers 100% of parameters, the description adds essential meaning beyond the schema: it explains the tri-state folder behavior, the clearFolder fallback for clients unable to send literal null, and the deep-merge partial-paths behavior for system. These details are critical for correct invocation.

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 opens with 'Update a world item — name, image, folder, or system data', naming a specific verb, resource, and the fields it affects. This clearly differentiates it from world-item-create/delete/filter/get and even from item-update via the 'world item' resource scope.

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 tool's use is implied correctly by its name and opening phrase, but it never explicitly says when to prefer world-item-update over alternatives like item-update. It does provide conditional guidance for clearFolder ('if your client cannot send literal null'), which is helpful but not tool-selection guidance.

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