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

Annotations already declare readOnlyHint/idempotentHint/non-destructive, so safety is covered; the description goes further by disclosing that routes render on a map where the host supports it, that a Remap link is always returned, and how the no-location path behaves. It does not say how a conflicting distance-and-duration pair is resolved or what happens when a start cannot be geocoded, which are the remaining behavioral gaps.

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-loaded with the use case, then exclusions, then return behavior, then the parameter constraint and fallback — a sensible order with no filler sentences. The opening sentence is dense and the loop concept is restated slightly, but nothing is genuinely wasted.

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 return-value burden and does so: map rendering plus an always-present Remap link. Combined with the exclusivity rule for start vs lng/lat and the fallback flow, an agent has everything needed to invoke this correctly.

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%, so the baseline is 3; the description earns above baseline by stating a constraint the schema never encodes — 'Give either start or lng and lat, never both' — plus a concrete place-text example and the no-start fallback. It adds little for the enum fields beyond what the schema already documents.

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 opening sentence names a specific verb (generate) and resource (routes) and pins the scope precisely: loop routes for cycling/running/walking with a distance or duration target. It also excludes what it is not ('directions from one place to another or for driving'), so an agent can separate it from the find_place sibling 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?

Explicit when-to-use, when-not-to-use, and a concrete fallback path: 'When the person has not said where, call generate_routes without a start' and let the map prompt for location. This is exactly the routing guidance an agent needs, including the edge case where the required context is absent.

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