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

Annotations only cover the safety profile (read-only, closed-world, non-destructive), and the description adds substantial behavior beyond that: cost ($0.99 via x402 or Builder/Pro key), no free trial, a free metadata endpoint, and the fact that ACI output is a suspended historical print per ADR 0006. The only blemish is that the 'no free trial' claim conflicts with the input schema, which tells the agent to omit api_key 'to use the free trial (1 call/day)' — an inconsistency against the schema, not the annotations.

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?

Most sentences carry real information (pricing, deprecation status, endpoint), but it opens with a rhetorical question that adds nothing for an agent and restates the free-metadata fact twice. The pricing/auth content would be better front-loaded as a single compact block rather than interleaved with marketing framing.

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 correctly compensates by enumerating the return contents (per-figure universe labels, methodology versions, trends, breakdowns, protocol comparison, reliability). It also discloses the deprecation caveat. The one gap is that the conflicting auth story between description and schema leaves the agent unsure whether a free call is possible.

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 schema already documents both month (YYYY-MM, default latest) and api_key, making 3 the appropriate baseline. The description adds cost/auth context but arguably degrades parameter semantics by contradicting the schema's free-trial behavior for api_key.

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?

The description states a specific resource and the exact payload contents ('the monthly State of Agent Commerce as structured JSON: every figure with its universe label and methodology version, plus trends, category breakdowns, protocol comparison and reliability'), so an agent knows what it retrieves. It never names or contrasts itself with any sibling (e.g. get_market_summary, get_category_detail), so differentiation is left to inference.

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?

It gives practical context — pricing path, that metadata is free at a separate endpoint, and that retained ACI blocks are historical — which implies when the tool is and isn't worth paying for. However, it offers no explicit guidance on when to pick this over the many sibling data tools, and no exclusions beyond the ACI note.

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