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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds real behavioral context beyond that: keyless/no-rate-limit access and, critically, a warning that category share_of_transactions is a share of categorized transactions only and that only the top 6 are returned so shares sum to <100%. That misinterpretation trap is exactly the kind of disclosure annotations cannot convey.

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?

The output list and the share-of-transactions caveat are front-loaded and dense with earned information. The 'citation number' aside and rhetorical question are mild filler, but most sentences carry weight.

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 carries the burden of describing return values and it does so, including the non-obvious share-percentage caveat. An agent can interpret the payload correctly without further docs.

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 tool takes zero parameters, so there is no parameter semantics to explain and the baseline is 4. The description instead spends its words on return-value semantics, which is the right allocation.

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 names the concrete outputs (daily transactions, USDC spend, unique buyer agents, live providers, top categories by share), so an agent knows exactly what resource this returns. It only implicitly distinguishes itself from siblings like get_category_detail; there is no explicit contrast. The rhetorical opening ('How big is agent commerce today?') adds flavor rather than precision.

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 states an invocation condition ('Keyless - no key, no payment, no rate limit'), which is genuinely useful access guidance. However, it never says when to choose this over get_category_detail, get_report_data, or other ecosystem-level siblings, leaving the routing decision to inference.

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