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

Annotations already declare read-only, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds context the annotations cannot: per-call cost of 0.001 USDC via x402, the PAYMENT-SIGNATURE header, and the fact that API-key clients pay nothing — materially useful for an agent deciding whether to call it. It does not describe the 'per-venue metadata' payload, which keeps it from a 5.

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?

Purpose and disambiguation come first in a single tight sentence, followed by a bracketed access note. The access note is verbose relative to the rest but carries genuinely actionable payment information, so it earns its space.

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?

A single-parameter read tool with full annotation coverage needs little more, and payment/auth mechanics are covered. The remaining gap is that 'per-venue metadata' is undefined and there is no output schema, so the agent cannot anticipate the response shape.

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?

Only one parameter, fully documented in the schema (100% coverage), which already gives an example ('BTC or ETH'). The description adds only that it must resolve to 'one specific token', which the schema arguably implies. Baseline 3 is appropriate; nothing substantive is added.

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 resource (exchanges listing a given token) plus the added value of 'per-venue metadata', which separates it from a plain exchange directory like list_exchanges. It also implicitly carves itself away from price tools, though it never names the sibling it differs from, so it stops short of a 5.

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 an explicit trigger ('when the user asks where a token trades or which venues carry it') and an explicit exclusion ('rather than for a price on any one of them'). What's missing is the named alternative — e.g. get_market_data or get_ohlcv for pricing — so the agent must infer the substitute.

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