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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds real behavioral context: the `type: monster` filter is baked into the call, results default to a compact shape, and `detail: 'full'` inlines full stat blocks. It stops short of covering pagination or rate behavior, but the value-added disclosure is solid.

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-loads the core purpose in the first clause and proceeds logically through sibling differentiation, response shape, and follow-up. Four dense sentences with no filler, though it is near the upper bound of ideal length.

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?

An output schema exists, so return values need not be spelled out, yet the description still summarizes the two response shapes. It covers routing, the baked-in filter, response detail, and chaining, leaving nothing an agent needs to call it correctly 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 baseline is 3. The description goes beyond the schema by explaining the implicit baked-in type filter (which is not even a parameter) and clarifying the practical effect of `detail: 'full'` (full stat block inline vs compact summary), adding meaning above the raw enum description.

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 ('Search authored monsters... the user owns, plus any stock template monsters') and explicitly distinguishes itself from the sibling `vault_search_characters`, explaining why the separate tool exists. An agent can tell exactly what this returns without opening either schema.

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?

Provides explicit when-to-use ('the right tool for creature stat-block lookups'), why-not-the-sibling ('vault_search_characters deliberately hides monsters by default'), and a follow-up pairing ('Pair with vault_get_character on a returned id'). Routing is unambiguous.

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