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

With no annotations, the description carries the full behavioral disclosure burden. 'Get' clearly implies a read-only operation, and the description explains the return content (side-by-side specs, pricing, market context). Yet it does not disclose prerequisites such as requiring an existing session with tracked vehicles, nor edge-case behavior like an empty session.

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 concise sentences. The first is front-loaded with the action and the object, and the second provides a meaningful use-case without fluff. 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 tool with no annotations and no output schema, the description gives a decent summary of the returned comparison but omits prerequisites and edge-case behavior (e.g., what counts as 'all vehicles', what happens if the session has zero vehicles). The rest of the context must be inferred from the session parameter and sibling names.

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 adds no additional parameter-level meaning; it only indirectly references the session and says nothing about agent_id. It neither helps nor hurts beyond the schema.

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 starts with a specific verb and resource: 'Get a structured comparison of all vehicles tracked in a session' and lists concrete content dimensions (specs, pricing, market context side by side). This makes the tool's function unambiguous and distinguishes it from siblings like cars_vehicle (single-vehicle data) and cars_session_add_car (mutation) even without naming them.

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?

'Great for helping the buyer decide' provides a clear, practical use case for the tool. However, it does not explicitly mention alternatives or any when-not-to-use conditions, stopping short of fully explicit routing guidance.

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