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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so safety is covered. The description adds the useful cap of 'up to 3 itineraries' and the leg structure, but since an output schema exists this is largely restating what structured data provides; no auth, rate-limit, or failure behavior is described.

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, front-loaded with purpose then return shape, then the prerequisite pointer — no wasted clauses. Minor wording friction ('of the TTC in Tbilisi') but nothing that obscures the call.

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 an 8-parameter tool with an output schema and annotations, the description covers the input form (coordinates), the geocoding step, and the shape and cap of results. What remains thin — how timing/preference affect results — is handled by the schema, so an agent could call 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 every parameter including timing, preference, kinds, and language is already documented with defaults and allowed values. The description only adds the constraint that points are coordinates (refining 'from'/'to') and adds nothing on timing/preference semantics. Baseline 3 is appropriate.

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 ('Plans a trip by public transport') with scope ('TTC in Tbilisi between two points, given as coordinates'). An agent can tell this is a routing/itinerary tool rather than a stop or timetable lookup, though it never names the route-level siblings (transit_get_route, transit_search_routes) it differs from.

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?

Gives a concrete prerequisite that selects a sibling: 'Use transit_search_places to get coordinates,' which tells the agent this tool cannot take addresses or names. It lacks any explicit when-not-to-use guidance versus the other transit tools, so it stops short of full routing guidance.

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