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

Annotations already cover read-only/idempotent/non-destructive, but the description adds the crucial non-obvious behaviors: this is a paid endpoint ($0.001/call), it returns an x402 request spec rather than the digest directly, invalid input is refused before any charge, and there is a 64 KB cap. Those are exactly the traits an agent cannot infer from 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?

Two dense sentences with the usage trigger front-loaded and no filler. It is on the longer side, but nearly every clause (pricing, URL, client requirement, input validation) carries distinct operational value.

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, so the description correctly explains what is returned (the exact paid request, response schema and example) and how to turn it into the actual digest. Combined with fully documented parameters, an agent has everything needed to call it correctly.

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 algo, text and encoding are already documented with enums and defaults. The description largely restates that (algorithm list, encoding list, size limit), adding no new syntax or format guidance beyond what the schema provides, so the 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+resource (checksum/digest of a string) and enumerates the supported algorithms and encodings. It is immediately distinguishable from siblings like util_base64 and util_jwt_decode without opening either schema.

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 a clear trigger condition, and the second sentence explains the actual invocation flow (call the returned URL with an x402/MPP client). It does not, however, name alternatives or explicitly exclude sibling utilities, so a 4 rather than a 5.

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