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

With no annotations present, the description carries the full behavioral burden and does a solid job: it discloses the payment amount and rail ($0.01 USDC on Base), that no account or API key is required, that failed calls are not charged, and that data is sourced from Coinbase Exchange with a Kraken cross-check. It stops short of stating rate limits, latency, or what constitutes a failure/billing boundary.

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 single most important fact for an agent ('Paid.'), then the payload contents, then cost, then auth and billing policy. It is telegraphic but every clause carries distinct decision-relevant information 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?

For a zero-parameter price feed with no output schema, the description supplies the returned fields, the data provenance, the price, the auth model, and the failure-billing policy — enough to call it correctly and predict the cost. The remaining gap is that it does not describe the response shape (JSON keys, units, timestamp fields) or error behavior beyond the no-charge promise.

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 add and the baseline of 4 applies. The description correctly avoids inventing argument details and instead spends its space on cost and data-source context.

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 exact resource (FARM/USD live price) and enumerates the returned fields (last, 24h open/high/low, % change, 24h and 30d volume), so there is no ambiguity about what the tool produces. Because the sibling set is a long series of per-coin tools, the symbol embedded in both name and description is what distinguishes it, and that is done correctly here.

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?

Usage is implied rather than stated: the description tells the agent it is paid, costs $0.01 USDC on Base, and requires no account or key, which is decision-relevant context for whether to call it. However, it never routes against alternatives — notably the generic sibling buy_crypto_price or any other buy_coin_* — and gives no when-not guidance, so the agent must infer that this is the FARM-specific option.

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