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

Annotations only declare readOnly/idempotent/openWorld, so the description carries the real behavioral burden and does: it discloses the x402 payment model, the $0.001 per-call price, the GET /util/hash endpoint, the P0 bearer-key path that makes the call server-side, and critically that bad input is refused before any charge. That pricing and pre-charge validation detail is exactly the context an agent needs before invoking a paid tool.

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 triggering condition and core capability are front-loaded, and every clause carries information (algorithms, size cap, payment path, key header). It is nevertheless a single run-on sentence that packs the key-purchase URL inline, which is dense enough to slow parsing of the two invocation modes.

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?

There is no output schema, and the description covers both the unpaid mode (returns an x402 request to replay) and the keyed mode (returns the actual digest), plus price and validation behavior, which is enough to call it correctly. The return payload shape in the unpaid mode remains slightly ambiguous in how it is phrased, keeping it just below 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 description coverage is 100%, so all three parameters are already documented, including the enum for encoding and the comma-list semantics for algo. The description restates the algorithm and encoding options and adds the 64 KB bound (already implied by maxLength), so it adds little meaning beyond the schema; 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?

The description states a precise verb and resource: compute a checksum/digest of a string, with the supported algorithms (sha256 default, sha1, sha384, sha512, md5) and the input encodings (utf8, hex, base64). It is distinguishable from adjacent siblings such as util_base64 or util_uuid because the hashing domain is stated explicitly.

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 triggering condition, and the description scopes usage with the 64 KB limit and the "no external call" / paid-call distinction. It stops short of naming when-not to use it or pointing at an alternative sibling, so it is clear context rather than full routing guidance.

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