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

Annotations already cover read-only, idempotent, open-world, and non-destructive behavior. The description adds valuable context beyond these: data updates 'approximately every 2 minutes from the TfL live feed,' no auth required, and source/licensing (TfL Open Data CC-BY). This enriches the agent's understanding of data freshness and access requirements. Not quite a 5 because it doesn't mention pagination or rate limits, but solid for a read-only endpoint.

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?

The description is efficient: first sentence states core function and return fields, second covers filtering, third covers freshness and use cases, fourth covers source/licensing. It is front-loaded with the main purpose and avoids fluff. Slightly longer than strictly necessary due to the use cases and source mention, but every sentence adds value.

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?

Given the output schema exists and annotations cover safety, the description is complete for an agent to invoke correctly. It includes the main result fields, filtering options, update cadence, auth requirements, source attribution, and licensing. Nothing critical 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?

Schema description coverage is 100%, so the baseline is 3. The description repeats query examples (Waterloo, Hyde Park, Soho, Paddington) already present in the schema, and the limit parameter is described in the schema as well. The description does not add new semantic meaning beyond what the schema provides. 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?

The description begins with a specific verb and resource: 'Get real-time availability of Santander Cycles... at all 800+ docking stations across London.' It clearly states the resource scope and differentiates from sibling tools like arrivals, journey_plan, and line_status by focusing on bike station availability. An agent can immediately understand what this tool provides.

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?

The description provides clear use contexts: 'useful for cycle hire planning, last-mile commuting, and real-time docking station capacity monitoring.' It also explains when the optional filter is appropriate. However, it does not explicitly mention alternatives or when not to use this tool, so it falls short of a 5 but is well above no guidance.

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