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

Annotations already declare readOnly and open-world, so safety is covered. The description adds genuinely non-obvious behavior: dual output formats (hex and base64), and a per-call price with the x402 payment endpoint, which annotations cannot convey. It stops short of explaining the free-trial/payment-requirements fallback documented in the schema.

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?

One sentence plus a parenthetical price note; the capability is front-loaded and the algorithm/output detail follows naturally. The pricing parenthetical is slightly clunky but earns its place by flagging a cost constraint.

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 no output schema, the description usefully tells the agent that both hex and base64 are returned, and it discloses pricing. What an agent still has to dig for — the free-trial behavior and the payment-requirements response — lives in the schema, which is acceptable at full coverage.

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 including the algo enum and the payment header are already documented. The description's algorithm list restates the enum rather than adding format or defaulting nuance, so baseline 3 applies.

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 (hash) and resource (string) plus the exact algorithm set and output encodings, which clearly separates it from siblings like encode or text_stats. An agent can tell at a glance this is a pure cryptographic digest, not an encoder.

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 three concrete use cases (commitments, idempotency keys, checks), which implies when to reach for it. However, it never states when NOT to use it or names an alternative (e.g., encode for non-cryptographic transforms), so selection guidance is only implied.

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