Compare cars

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

Annotations already declare read-only, idempotent, non-destructive, closed-world, but the description adds substantial context they cannot: what the response contains (specs, BDT prices, optional QC summaries, not_found/unavailable/price-coverage counts), how unknown prices become null rather than zero, and that invalid arguments produce isError=true with structuredContent.error. It also scopes out valuation, seller contact and reservation.

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-loaded with purpose and input sourcing, then degrades into a fairly dense chain of edge-case clauses. All content is substantive, but the price-coverage sentences are packed tightly enough to slow scanning; slight trimming would help.

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?

With no output schema, the description carries the return-value burden and does it well: field-level contents, count fields, null handling, error shape, and the market-scope caveat on cheapest_listing_id. Nothing an agent needs to interpret results 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?

Schema description coverage is 100% and the schema already states the 2-4 range, the 'not VINs or URLs' constraint, and the distinct-listings/alias caveat. The description largely restates this ('Repeated IDs/aliases are not independent price evidence' mirrors the schema text), so it adds little beyond what structured data already provides. Baseline 3 applies.

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 (compare) plus resource and cardinality (two to four JOY vehicle listings side by side), and explicitly distinguishes itself from get_vehicle for single-car lookups and from search_vehicles as the ID source. An agent can route between the three siblings without opening any schema.

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?

Names the upstream tools that supply inputs, the alternative tool for the single-vehicle case, and the conditions under which a cheapest result is meaningful (at least two distinct listings with positive stated prices; price_comparison_complete flag). Both when-to-use and when-not-to-trust-the-output are spelled out.

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