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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely non-redundant context: that results are saved-only with no store requests, that the dataset includes unverified outside submissions (a data-reliability caveat), and that output carries evidence labels and Wilson 95% intervals plus CC-BY-4.0 attribution terms.

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 the verb and resource, and nearly every clause carries information (scope, agent paths, returned statistics, saved-only constraint, license). The middle is a dense run-on sentence, and the trailing "CC-BY-4.0" is a bare license token, so it is efficient but not maximally clean.

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 takes on the burden of describing returns and does so: n, dates, evidence labels, Wilson 95% intervals, unverified outside submissions, and per-agent-path breakdowns. Combined with annotations covering the safety profile and the schema covering the one parameter, an agent has everything needed to call and interpret this tool.

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?

There is a single optional parameter (include_stores) and schema description coverage is 100%, so the schema already documents the per-store grid toggle. The description adds nothing about this parameter, which is the expected baseline when the schema does the work.

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 ARC's open agent leaderboard") and immediately scopes the content: cart success over the fixed ARC-100 v1 test set for the enumerated agent paths (browser shoppers A-E, UCP, storefront MCP). The "Saved results only; no store requests or model calls" clause separates it from live-check siblings like can_agent_checkout and precheck without the agent needing to open another 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?

Gives a clear selection condition: this returns saved, precomputed results rather than issuing store requests or model calls, which routes the agent away from live-probe siblings. It does not name any alternative explicitly (e.g. submit_leaderboard_run for writes, or a live-check tool when fresh data is needed), so the routing is implied rather than spelled out.

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