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

Annotations only state the safety profile (readOnly=false, idempotent=false, destructive=false). The description adds the crucial behavior the annotations cannot convey: system is DEEP-MERGED, pass only changed paths, and arrays are replaced whole, which is a real data-loss caveat. That is exactly the value-add expected beyond annotations.

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?

Purpose is front-loaded in the first clause, then merge semantics, then an example, then dnd5e path hints and the damage-tool routing. Every sentence carries distinct information with no filler or repetition of the schema.

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 7-param nested-object mutation tool with no output schema, the description covers the hard parts: merge behavior, tokenId scoping, and common paths. The notable gap is that the schema declares zero required parameters and the description never says an actorId or tokenId must be supplied for the operation to make sense.

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 already 100%, so the baseline is 3. The description goes further by illustrating deep-merge semantics for `system` with a worked example and naming common dnd5e paths, plus disambiguating tokenId vs actorId. It doesn't compensate for the odd schema fact that no parameter is required.

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?

Specific verb+resource: 'Update an actor's name, image, folder, or system data', plus the tokenId scope variant. It explicitly names an alternative (dnd5e-apply-damage) and reaches into the actual mechanic (deep-merge of system), so an agent can tell it apart from actor-create, token-update, and item-update without opening schemas.

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?

Gives a concrete when-not: 'For HP after damage prefer dnd5e-apply-damage (resistances, temp HP)', and clarifies that tokenId targets one token's own actor instead of actorId. It does not address the potential confusion with token-update for token-level changes, so the routing is good but not exhaustive.

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