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

Annotations already indicate this is a write operation (readOnlyHint=false) and not destructive (destructiveHint=false). The description adds the constraint that it updates 'active' effects, which is useful context. However, it omits important behavioral details such as the fact that the 'changes' array replaces existing changes (only in the schema) and that duration is also updatable, which is not mentioned in the description.

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 a single, concise sentence that is front-loaded with the core action and scope ('Update an existing active effect on an actor'). It lists the key modifiable fields without redundancy, making it efficient and easy to parse.

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 tool has 7 parameters, nested objects, and no output schema, the description is quite brief. It does not mention that duration can be updated, nor does it explain that the changes array replaces existing changes (a potentially surprising behavior). The agent would need to read the schema to fully understand the tool's semantics, so the description is only partially complete for this complexity level.

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 the schema fully documents all parameters. The description provides a high-level summary of what can be modified but omits duration and does not add per-parameter meaning beyond the schema. It also does not explain the replacement semantics for 'changes', which is described in the schema but not reinforced.

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 clearly states the tool updates an existing active effect on an actor and lists the modifiable fields (name, icon, disabled state, changes). This distinguishes it from siblings like effect-create, effect-delete, effect-list, and effect-toggle-status, which have different purposes.

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 implies the tool is for updating existing effects but does not explicitly contrast with alternatives or state when not to use it. It does not mention effect-toggle-status for toggling disabled state or effect-create for new effects, leaving the agent to infer the appropriate context from the schema and tool names.

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