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

With no annotations provided, the description carries the full burden. It adds useful behavioral context: the geographic scope (British inland waterways), the proximity radius is implied by the schema's 'approx. 15 km' note, and it discloses the unclaimed-listing claim feature with a URL. It doesn't describe result format or pagination, but for a straightforward search tool, this is reasonable.

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?

The description is three sentences, front-loads the core action, and uses a bullet-like list for categories. The list is long but informative. The final sentence about unclaimed listings is somewhat tangential but still relevant to what the results may contain. It is efficiently written without significant waste.

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?

Given no output schema, the description reasonably sets expectations about what is searched and what types of results to expect (business listings with an unclaimed marker possibility). It covers the geographic scope, filtering options, and a special feature. It omits details like sorting or result count, but those are not essential for a search tool at this tier.

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 schema already documents all parameters. The description mentions 'free text, category, or proximity to a place' which maps to query, category, and near, but adds no new detail beyond the schema's property descriptions. It earns the baseline 3, not higher.

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?

The description begins with a specific verb and resource: 'Search Canal Nav's directory of waterside businesses on the British inland waterways.' It enumerates concrete business categories and clearly distinguishes itself from sibling tools (find_place, route planning, closures), which serve different purposes.

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 states the search scope and available filters ('Filter by free text, category, or proximity to a place'), giving clear context for when to use this tool. It does not explicitly name sibling alternatives or exclusion criteria, but the context is sufficient for an agent to know when search_directory is appropriate.

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