marta_train_arrivals

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

Annotations include readOnlyHint: true, and the description adds meaningful behavioral context: 'real-time', 'all stations', 'all active trains across the entire MARTA rail network', and details the returned data fields. This goes beyond the annotation without contradicting it.

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 two sentences: the first states the primary function and scope, the second lists the output fields. Every sentence provides useful information, with no redundancy or filler.

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 no output schema, the description effectively explains what the tool returns (destination, direction, line, station, arrival time, wait seconds, GPS). It could mention the output structure (e.g., array of predictions), but for a zero-parameter read-only tool, it is sufficiently complete for an agent to use 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?

The input schema has zero parameters, and schema coverage is 100%, so there is no parameter documentation burden. The description correctly omits parameter details, and no parameter semantics are needed.

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 uses a specific verb ('Get real-time MARTA rail arrival predictions') and names the resource ('all stations in Atlanta, GA'), clearly distinguishing it from sibling transit tools. It also enumerates the returned fields, leaving no ambiguity about what the tool does.

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 context: it is specifically for MARTA rail arrivals across the entire network. It does not explicitly mention alternatives or when not to use it, but the scope is unmistakable, differentiating it from other transit arrival tools in the sibling list.

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