cta_bus_arrivals

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

Annotations include readOnlyHint=true, so the description already builds on that safety profile. It adds value by disclosing the return contents (predicted arrival times, route, direction, destination, delay status) and noting that stop IDs are numeric. This sufficiently covers behavior beyond the annotation.

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 concise sentences, front-loaded with the primary action and resource. The second sentence lists return fields and includes a note about stop ID format. No redundant or filler content.

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 single-parameter tool with no output schema, the description adequately covers what it does, what it returns, and how to get the input. It could mention error handling for invalid stop IDs, but given the tool's simplicity, the information provided is sufficient for an agent to select and invoke it 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 schema already covers stop_id with a clear example and type. The description adds guidance on where to find stop IDs (bus stop signs or the CTA website), which helps the agent obtain a valid value. This is a modest but useful supplement to the schema's 100% coverage.

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 clearly states the tool's function: 'Get bus arrival predictions for a CTA (Chicago) bus stop.' It specifies the resource (CTA bus arrivals) and distinguishes it from sibling rail/transit tools. The scope is precise (CTA bus, not trains or other transit systems).

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 implies the use case: when you need CTA bus arrival predictions. It provides practical guidance on obtaining stop IDs (from signs or the CTA website). However, it does not explicitly name alternatives or state when NOT to use this tool, though the CTA-specific wording is clear in context.

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