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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the safety profile is covered. The description adds a genuinely useful trait beyond that: it 'never invents figures; returns null when not stored', which tells the agent how to interpret missing data. It stops short of describing result ordering, count limits, or pagination behavior.

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 short sentences, front-loaded with the resource and filter scope, then the workflow pointer, then a data-quality caveat. No wasted wording.

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?

With 7 optional parameters, no required params, and no output schema, the description should say what happens when no filters are supplied and roughly what a 'trail summary' contains. It covers the null-handling contract but leaves the unfiltered/default behavior and result size unspecified.

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 only 14% (just sacScale), so the description carries most of the burden. It names country, region and distance as filter concepts but adds no format, matching, or unit semantics, and leaves maxTypicalDays and permitRequired entirely undocumented in both schema and 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 and resource ('Returns trail summaries') plus the filtering axes, and names the sibling it feeds into (get_trail), so an agent can distinguish it from get_trail/get_geojson. It falls short of 5 because the stated filter set (country, region, distance) omits three real filter dimensions present in the schema (sacScale, maxTypicalDays, permitRequired).

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?

Explicitly says to use this 'to shortlist trails before get_trail', which gives a clear position in the workflow relative to a named sibling. It does not state when not to use it (e.g. no guidance on whether zero filters is acceptable or when to prefer get_geojson/plan_permits).

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