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

Well beyond the annotations: it discloses cost ($0.001 per call), that bad input is refused before any charge, that the default behavior performs no external call and instead returns a ready-to-execute x402 request, and that supplying a Bearer p0k_ key causes the tool to make the paid call and deduct the price. These are exactly the operational facts an agent needs and none are in the structured fields.

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?

The trigger is front-loaded correctly, but the body is a dense run-on that mixes three distinct concerns (hashing parameters, payment mechanics, key purchase URL) into one sentence chain. The key-buy URL and purchase instructions are verbose relative to their decision weight.

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 carries the return-value burden and mostly does: it explains that the default path returns an x402 request plus response schema and example, while the keyed path returns the digest itself. The dual return mode is slightly ambiguous about which shape you get, keeping it from a 5.

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 the schema already documents algo, text, and encoding including defaults and the enum. The description adds only the 64 KB size limit and the notion of hex digests as output, which is minimal marginal value over the schema, 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?

Opens with a specific verb and resource: compute a checksum/digest of a string, and enumerates supported algorithms (sha256 default, sha1, sha384, sha512, md5) and input encodings. This clearly separates it from sibling util_* tools like util_base64 or util_jwt_decode.

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?

"Use when you need a checksum or digest of a string" gives an explicit trigger condition, and the flow states when the paid-call path applies (P0 access key present) versus when you only get the x402 request to execute yourself. It does not explicitly name a competing sibling or state when not to use it, so it stops short of a 5.

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