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

Beyond the readOnlyHint and openWorldHint annotations, the description discloses important behavioral details: the data is aggregated level-2 only, the source is Coinbase Exchange rather than Advanced, calls cost $0.002 in USDC per successful call via x402 on Base, Solana or Arc, and failed calls are not charged. This adds substantive context an agent needs before invoking a paid data endpoint.

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 description is front-loaded with the core resource and scope, followed by the enumerated metrics and payment details. It is dense but every sentence and metric list contributes useful selection or invocation context, with no 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?

Given the tool has an output schema, the description does not need to explain return values in detail. It sufficiently covers the source venue, product scope, aggregation level, pricing model, and payment behavior, which is complete for an agent to decide whether and how to call it.

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 schema already documents the single required parameter at 100% coverage, including examples like BTC-USD and ETH-USD. The description adds only that the order book is for one product, which is implied by the singular required parameter, so the baseline score for high schema coverage is appropriate.

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 clearly states a specific resource and scope: Coinbase Exchange US spot order book for one product, with named fields such as best bid/ask, spread, USD depth, 24h volume, RFQ volume, and high/low. It also distinguishes the data source from Coinbase Advanced and other venues, though it does not explicitly name the nearest sibling tool for historical orderbook candles.

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 clear usage context by specifying that the tool is only for Coinbase Exchange US spot data and not Coinbase Advanced or other venues. However, it does not explicitly route the agent to alternatives for related needs such as historical candles or product metadata.

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