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

Annotations already declare readOnlyHint=true, but the description adds genuinely useful context the annotations cannot convey: that the transport is a POST (via 'POST /v1/lists/query') yet the operation is non-mutating. That is exactly the kind of trap an agent could otherwise fall into. It does not discuss pagination behavior, but the schema covers page/results_size.

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?

Two tight sentences, with the core purpose front-loaded and the non-obvious safety note immediately after. Every clause earns its place; nothing is padding.

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 3-parameter, all-optional read tool with no output schema, the description covers purpose, transport, and mutation safety. The only residual gap is what a result looks like and how filtering narrows results, which the schema partially handles anyway.

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% – page, filters, and results_size each carry their own documented semantics, including the {field, op, value} filter shape. The description adds nothing beyond this, so the baseline of 3 applies.

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 ('Find') and resource ('allow/deny lists defined in the environment'), and the resource granularity (lists, not items) implicitly separates it from castle_search_list_items and castle_get_list. It stops short of naming a sibling or an exclusion, so it is clear rather than maximally disambiguating.

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?

Usage is only implied: the agent can infer this is for locating lists when the exact list ID is unknown, but there is no explicit when-to-use, when-not-to-use, or pointer to an alternative such as castle_get_list for known IDs.

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