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

Annotations already cover safety (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), but the description adds genuinely new behavioral facts: it reads only saved checks, issues no store requests or model calls, and labels each figure as Measured / Inferred / Not measured. The license note (CC-BY-4.0) is a minor extra.

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?

A single dense, front-loaded sentence that covers scope, dimensions, evidence labels, data source and license in ~45 words. No filler, though the compressed phrasing (four verbs in one clause) takes a moment to parse.

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 reasonably: it says the output is counts per protocol plus evidence labels. The only omission is output shape/pagination detail, which is minor for a single-parameter read-only aggregate.

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% with a single optional enum parameter, so the schema already documents the protocol id fully. The description mirrors the enum values (UCP, ACP, PAP, WebMCP, MCP, payments) but adds no syntax or behavior detail beyond what the schema states. 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 (Read) and a specific resource (ARC's neutral Protocol Matrix), then enumerates exactly which protocols it covers and what dimensions it reports (declare, validate, answer, transact). It is clear what the tool returns, though it never names or contrasts itself with siblings like agent_commerce_adoption or precheck.

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 clause 'Saved checks only; no store requests or model calls' tells the agent the data source is pre-computed, implying it should be used for aggregate overview rather than live lookups. However there is no explicit when-to-use statement and no named alternative for the case where an agent wants per-store or live data.

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