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

Adds substantial context beyond the annotations: no upstream request is made, missing/warming snapshots mean unavailable rather than empty, cache age is not publication age, and a loaded snapshot does not prove live service. These are exactly the interpretive pitfalls an agent needs.

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-loads what is inspected, then follows with tightly scoped caveats. Every sentence earns its place, with no repetition of annotations or title.

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 zero parameters, an existing output schema, and rich annotations, the description is complete. It covers purpose, non-behaviors, and interpretation risks without needing to explain return values.

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, so the baseline is 4. The description correctly adds no parameter detail because none exist.

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: inspect local GTFS snapshot state, enumerated as load age, calendar validity, row counts, and skipped rows. The 'local' qualifier and the final caveat ('does not prove live arrivals') distinguish it conceptually from live transit siblings such as next_departures or transit_line.

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 makes clear this is a local snapshot diagnostic and explicitly says no upstream request or refresh occurs, which implies when it is appropriate. However, it does not explicitly name alternatives or state when to prefer this over siblings like istanbul_health or istanbul_get_dataset.

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