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

Annotations already declare readOnly=true, idempotent=true, and openWorld=false, so the safety profile is covered. The description adds behavioral value by disclosing what the result contains (route counts and slugs) and that the slug is the key for chaining into other tools, which is not derivable from annotations or the empty schema.

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 sentences, no filler: the first defines the tool and its output, the second tells the agent exactly what to do next. The payload description is front-loaded before the chaining guidance.

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 no output schema, the description carries the burden of describing returns and does so at a high level (parks, route counts, slugs). Minor gaps remain, such as whether the list is a complete static catalog or may change, but nothing needed to invoke it correctly is 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?

The tool takes zero parameters, which sets a baseline of 4. The only parameter referenced (national_park) belongs to sibling tools, and the description correctly frames it as an output-to-input handoff rather than a parameter of this tool.

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 ("List the UK National Parks") plus a scoping qualifier ("Skamper covers") and the response payload (route counts and slugs). An agent immediately knows this is a discovery/enumeration tool rather than a route-search tool.

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 routes the agent forward: "Use the slug with routes_in_national_park or search_routes (national_park=...)", naming both relevant siblings and even the parameter to pass. It lacks an explicit when-not-to-use clause, but for a zero-argument enumeration tool the usage context is effectively unambiguous.

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