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

Annotations cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds substantial non-redundant behavior: results come from saved checks only, no fetch or scan, per-domain counting against a shared 60/min limit, partial results returning reason rate_limited with retry_after_seconds, and >100 inputs being refused. It even forecloses a likely misread ('not_recorded and known:false are not a no') and states the advisory-only / no-payment boundary.

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?

Dense but front-loaded — purpose, return shape, then behavior and limits in descending priority. Some tail material (the raw POST path, CC BY 4.0 attribution, 'ARC stops before payment') is marginally useful and could be trimmed, but nearly every sentence carries operational information.

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 so: per-input objects with an input field and a routes[] list enumerating the route types (ucp, ucp_mcp, storefront_mcp, cart_link, browser) and their evidence/staleness fields. Combined with the rate-limit and failure semantics, an agent has what it needs to call this 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 single parameter is fully described in the schema, so the baseline is 3, but the description adds real meaning beyond it: each domain consumes one read of the shared rate-limit budget, ordering of results matches input order, and more than 100 is rejected rather than truncated.

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?

Opens with a specific verb and resource plus scope: 'the precheck read for up to 100 store domains or URLs in one call', and immediately states the return shape (one object per input, in order). It implicitly and explicitly separates itself from the single-domain sibling by naming 'precheck' as the shared rate-limit counterpart and framing the bulk case as many-per-call.

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?

Gives clear when-not guidance: 'Saved checks only. Does not fetch any store and does not start a scan', so an agent knows this is not a live scan trigger. Rate-limit behavior and the >100 refusal are spelled out, but it never explicitly says 'use precheck instead for a single domain', leaving the sibling routing to inference.

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