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

Annotations already declare the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false). The description adds targeting semantics (per-token application) beyond that, but says nothing about whether omitted fields are preserved (partial vs full update), what 'changes' replacement implies for existing data, or any permission requirements.

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?

A single front-loaded sentence with the entity affected stated first and the mutable field list trailing. Efficient, though the trailing field enumeration is partly redundant with the parameter names and the shouted 'ONE' is a little stylized.

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 9-parameter mutation tool with nested objects and no output schema, the description plus 100%-covered schema and safety annotations give an agent enough to invoke it. The remaining gap is update semantics (replace vs merge, and how 'changes' interacts with a tokenId-scoped effect) which neither description nor annotations resolve.

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% across all 9 parameters, including the nested changes/duration objects and mode enum inlined in the schema, so the baseline is 3. The description's trailing field list (name, icon, disabled, changes, duration) merely restates a subset of the schema without adding format or interaction detail.

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 (Update) and resource (existing active effect), scopes it correctly ('on an actor, or on ONE token via tokenId'), and enumerates the mutable fields. 'Existing active effect' cleanly separates it from sibling effect-create, effect-delete, and effect-toggle-status.

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?

Implies the tool is for modifying an effect that already exists, and it does route the agent between actorId and tokenId targeting ('on ONE token via tokenId'). However, it never states when to prefer effect-toggle-status over setting 'disabled' here, nor any preconditions such as needing the effect to be found via effect-list first.

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