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

Annotations already declare readOnlyHint=true and openWorldHint=false, covering safety and scope. The description adds what data fields the response contains, which is beyond the annotations but not contradictory. It does not discuss pagination or rate limits, but given the simple list nature and closed world, this is sufficient context.

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 deliver the purpose, return fields, and usage context without redundancy. The core action is front-loaded, and the downstream tool linkage is a practical addition. Every word earns its place.

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 parameterless list tool with an output schema and annotations declaring read-only and closed-world behavior, the description provides the key information: what it returns, and why it matters (agency IDs for other tools). Nothing an agent needs to call it correctly 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?

The tool has zero parameters, so there is nothing to describe. The schema is empty and coverage is 100% vacuously. Per the rubric, baseline for 0 parameters is 4, and the description does not need to compensate for any parameter documentation gap.

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 action ('List all transit agencies') and resource scope ('served by this OneBusAway instance'). It also specifies the return fields (IDs, names, contact info, timezone, coverage center), which distinguishes it from any sibling that might return agency data with different scope. No ambiguity.

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 explicitly notes that agency IDs are needed for two downstream tools, implying when to use this tool (prior to those). It does not mention alternatives because there are none among siblings that list agencies. While it doesn't explicitly say 'use this when you need a list of agencies,' the context is clear and useful for an agent planning a sequence of calls.

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