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

Annotations already declare readOnlyHint=false, destructiveHint=false, and idempotentHint=false, covering the safety/mutation profile. The description adds a useful behavioral note that changes carry string values and follow dnd5e data paths ('other systems differ'), plus the single-token scoping caveat. It does not address permissions, whether an existing effect is overwritten, or what happens on invalid paths.

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?

Front-loaded with the core action and scope, followed by the changes/mode explanation and a compact worked example. It is appropriately sized for a 10-parameter nested tool, though the example JSON is dense and the final system-compatibility clause could be tightened.

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?

Despite 10 parameters and nested objects with no output schema, the description covers the two aspects an agent is most likely to get wrong: the actor-vs-token targeting and the shape/semantics of 'changes'. Remaining fields (duration, statuses, disabled, origin, img) are self-documenting at 100% schema coverage, so nothing critical is missing.

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, but the description meaningfully exceeds it: it provides a concrete worked example of a 'changes' entry and warns that paths are dnd5e-specific while other game systems differ. That path/format guidance is real added value over the raw schema, elevating it above baseline.

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+resource ('Add a custom active effect') and scopes the target precisely ('to an actor, or to ONE token via tokenId'). It distinguishes itself from the effect-update/effect-delete/effect-list siblings by making clear this is the creation path, and it names what is being created (buff, debuff, custom condition).

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 creation use case and explains the actorId-vs-tokenId selection ('instead of actorId: that token's own actor'), which is useful routing. However, it never explicitly names effect-update, effect-delete, effect-toggle-status, or effect-list as alternatives, nor states when NOT to use this tool (e.g., to modify an existing effect).

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