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

The description says to 'Arm' an inventory item, which implies a state-changing mutation, while annotations declare readOnlyHint=true. This directly contradicts the annotation and is comparable to a 'create' tool marked read-only. No other behavioral context is provided.

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 two short sentences with no filler. The core action and purpose are front-loaded, and the itemIndex clarification is useful and brief.

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?

Although the schema and output schema fully document parameters, the description omits usage context and, more importantly, the readOnlyHint contradiction makes the tool's actual behavioral contract unclear. An agent could be misled into thinking the call has no side effects.

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%, so per baseline the description need not add much. The description repeats 'itemIndex is 0-based' which the schema already states, and adds no new semantic information beyond what the schema provides.

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 names a specific verb ('Arm'), a precise resource ('Last Frame inventory item'), and the purpose ('for the next move'), making the tool's function immediately clear. It is distinguishable from siblings like choose_last_frame or start_last_frame because no other sibling describes arming an inventory item.

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 gives no guidance on when to use this tool relative to alternatives, no sequence context, and no prerequisites. While the schema mentions runId comes from start_last_frame, the description itself does not explain where this tool fits in the Last Frame workflow.

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