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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds genuinely non-structured behavior: a $0.05 per-successful-call price, payment via x402/USDC on Base, and the fact that it returns the digest plus input byte length plus the resolved algorithm identifier. It stops short of describing error/failure behavior or what happens on hash-size limits beyond what the schema states.

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?

Effectively three front-loaded sentences: capability and algorithm coverage, input/output formats, then return values and price. Every clause carries information; no filler, no repetition of the title verbatim beyond the leading label.

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 6-parameter, 100%-documented, non-destructive utility with no output schema, the description is close to complete: it covers algorithms, input encodings, output encodings, return shape, size constraints (via schema) and cost. The only omission is failure/validation behavior, which is minor for a pure computation tool.

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 description coverage is 100% and all six parameters carry enum lists and descriptions, so the baseline is 3. The description restates the algorithm list and the input/output encodings but adds no new semantics — it never explains, for example, how hmac_key_encoding interacts with hmac_key or why a caller would pick base64url over base64.

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?

Opens with a specific verb+resource ("Hash generator: compute a cryptographic digest") and enumerates exactly which algorithms and encodings are supported. An agent can tell immediately that this is a pure digest computation tool, distinct from every sibling in the list (no sibling performs hashing; jwt_decode and solidity_function_selector are the nearest crypto-adjacent tools).

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 by the clear scope statement rather than stated: nothing says when to prefer this over alternatives or when-not to use it. In practice no sibling overlaps, so the risk of misselection is low, but the description does not explicitly route the agent or state prerequisites beyond the payment note.

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