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

Annotations only supply readOnlyHint=false and openWorldHint=false — notably no destructiveHint — so the description carries most of the burden and does so: it discloses that prior words are overwritten, that pre-existing words retain their comparison method, that sibling rules are preserved, and that adding words is billing-gated. It does not describe the response or error behavior for an invalid routeId or duplicate words, which keeps it short of a 5.

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 action, then constraints, then edge cases; there is no filler. The single dense paragraph with nested parentheticals is harder to scan than a short bulleted form would be, which is the only real deduction.

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-required-parameter mutation with full schema coverage and no output schema, the description covers the destructive replacement, tariff gating, and the stop/start overlap invariant. It still leaves the agent guessing about the return value and what happens when a word conflicts with an existing one, so it is adequate rather than complete.

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% and each parameter already documents empty-list and case-sensitivity semantics, so the baseline is 3. The description adds one genuinely new parameter-level rule beyond the schema — that a word kept from the previous set retains its own comparison method — which is useful but narrow.

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 first clause names the exact verb and resources: sets stop-words and start-words for a route. It also scopes the operation against sibling concerns by stating that replacements, attachments and disabled words are untouched, so an agent can tell it apart from route_set_replacements/route_set_attachments without opening any 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?

It gives actionable conditions: new words require a paid tier, while removing words works on any tier, and each call fully replaces the passed lists (empty list clears). It does not explicitly enumerate alternative tools or say when to prefer route_set_rules/route_configure, but the 'other rules stay as-is' sentence makes the boundary inferable.

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