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

Annotations declare readOnlyHint=false, idempotentHint=false and openWorldHint=true, but the description adds genuinely new behavior: a $0.02 per-call cost, the USDC-on-Solana x402 payment protocol, and the exact retry sequence with _meta["x402/payment"]. That is the critical non-obvious behavior for this tool; it stops short of covering failure modes, timeouts, or what happens on payment rejection.

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?

Three short sentences, front-loaded with what the tool returns before the payment mechanics. The payment parenthetical is dense but every clause is actionable and none is filler.

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?

Payment and data-source context are complete, but with no output schema and no mention of the return shape, an agent cannot tell what an aggregated HS flow response looks like or whether results are paginated. For a 7-parameter data tool with no output schema, that is a real gap.

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 each of the 7 parameters documented inline, so the schema carries the burden. The description only echoes that flows are HS-based and reporter-scoped (EU-27 or CA) and adds no format or validation detail beyond the schema.

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 ('Aggregate HS trade flows') and names the underlying data sources (Comext EU, StatCan CA-US), which is far more informative than the name alone. It does not distinguish itself from the sibling stats_indicator, so an agent must still infer which stats tool fits a macro-economic vs trade question.

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?

There is strong procedural guidance on how to pay via x402 and an HTTP fallback, but no statement of when to use this tool rather than stats_indicator or how to pick EU vs StatCan reporters. Usage context is implied rather than explicit.

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