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

Annotations only say readOnly/openWorld; the description adds the substantive traits an agent needs: latest-candles-only semantics, a 300-candle upstream cap, an explicit $0.002 USDC cost per successful call, the x402 payment rails (Base, Solana, Arc), and the fact that failed calls are free. That payment/authorization requirement is exactly the kind of behavioral disclosure structured fields do not carry.

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?

Front-loaded with the core verb+resource, then constraints, then cost — three tight sentences with no filler. The pricing sentence is longer but every clause (amount, currency, rails, failure policy) carries decision-relevant information.

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 an output schema present and full param coverage, the description needs only scope, limits and cost, and it supplies all three. The one soft spot is the mismatch between 'Coinbase returns up to 300 per call' and the schema's limit max of 100, which could leave an agent unsure which cap applies.

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 all three parameters are already documented in the schema, which sets the baseline at 3. The description does add a readable mapping of granularity labels (1m, 5m, 15m, 1h, 6h, 1d) and a product example, but it does not cover the limit range or reconcile the 300-candle upstream cap with the schema's limit maximum of 100.

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+resource (Coinbase Exchange OHLCV candles for one product) plus the current best bid/ask, with a concrete example product and the exact granularity ladder. This is clearly distinguishable from siblings like finance_coinbase_assets, finance_coinbase_exchange_products or crypto_coinbase_spot_exchange without opening any schema.

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?

The description implies usage (historical/latest candle data for a single product) and discloses the important constraint that only the LATEST candles are returned, capped at 300 per call. However, it never names an alternative tool or states when to prefer a different sibling for depth, tickers or price feeds — the routing decision is left to inference.

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