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

With no annotations, the description carries the full burden and does so well: no login, no new scan, two distinct lanes (catalog HTTP check and browser cart), the exact semantics of `agents_can_buy`, the boundary that ARC stops before payment and is not a completed order, that the catalog check does not alter the score, and that a missing score is not a zero. These are exactly the non-obvious behaviors an agent needs before interpreting results.

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?

Purpose and the routing rule are front-loaded, and the trailing caveats ('not a completed order', 'missing score is not a zero', 'results are advisory') each carry real interpretive value. The text is dense but a few caveats could be compressed without losing meaning.

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?

There is no output schema, so the description must explain returns, and it does: score, evidence, and both lanes. Combined with the interpretation caveats and the precondition on store URLs, an agent has everything needed to call it and read the answer 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?

Schema coverage is 100%, so the baseline is 3, but the description adds meaning beyond the schema by framing brand/URL/category as alternative entry points ('Pass a brand, URL, or category') and constraining URL to one already on the ARC Index. The `q` free-text parameter is never mentioned in the description, keeping it from a 5.

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 and resource: read whether an AI agent can reach checkout for a brand already on the ARC Index, including the scope restriction that the brand must be indexed. It distinguishes itself from `precheck` explicitly ("For any store URL, call precheck first") but leaves its relationship to `can_agent_checkout`, `find_agent_ready_stores`, and `agent_leaderboard` unstated, which are the most likely confusable siblings.

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?

Provides concrete user-utterance patterns ('is <brand> agent-ready?', 'how does <brand> score on ARC?', 'which <category> brands...') plus an explicit routing rule to a named alternative for the store-URL case. No exclusion guidance against the other readiness-related siblings, so it stops short of full when/when-not coverage.

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