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

Annotations only declare readOnly and openWorld, so the description carries the real burden and delivers: the call is PAID ($0.005 USDC) and returns payment requirements plus an HTTP URL for x402. What it does not disclose is the payment mechanics — whether the tool itself settles payment or just hands back a challenge, and whether repeated calls are charged each time.

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, each doing distinct work: what it returns, what it costs, and which sibling to use instead. Cost and the paid flag are front-loaded in capitals so a scanning agent cannot miss the billing implication.

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?

No output schema exists, and the description compensates by naming what comes back (payment requirements + HTTP URL for x402). Combined with the pricing disclosure and sibling routing, an agent has enough to decide and call correctly; only the x402 handshake sequence remains implicit.

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 the baseline is 4. The description correctly says nothing about arguments and instead spends its words on cost and return shape, which is the right allocation for a parameterless tool.

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 ('live BTC/ETH/SOL/HYPE spot prices') with an explicit scope qualifier ('only') and a price point. An agent can immediately distinguish this from get_market_pulse (broader market data bundle) and get_market_sample (free preview).

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?

Explicitly routes the agent: 'Prefer get_market_pulse when you also need Fear & Greed, funding, or DeFi' names the alternative and the exact condition that selects it, and 'Free preview: get_market_sample' gives the zero-cost fallback. Both siblings are addressed with concrete selection criteria.

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