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

Beyond the annotations (readOnly, idempotent, openWorld, non-destructive), it discloses that input is not stored, what the response contains (hex, base64, short prefix, byte length), and the exact cost model with the payment mechanisms (x402 via params._meta or HTTP, X-API-Key credits). The free-tier quota of 10 calls/day and $0.001/call overage is exactly the kind of operational fact annotations cannot express.

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?

Front-loaded with the purpose, then normalization, then return shape, then privacy, then pricing — a sensible priority order packed into four compact sentences. The payment-mechanism sentence is dense but justified for a pay-per-call tool; nothing is redundant enough to cut.

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?

An output schema exists, so return values needn't be spelled out, and the description still summarizes them helpfully. Privacy, cost, and normalization are all covered; the only mild gap is the absence of guidance on whether default algo is sha256 and how the paid path fails when no payment is supplied.

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 four parameters are already documented, and the baseline is 3. The description does add marginal meaning by glossing normalize as 'lf, trim, json canonical', clarifying that json implies canonicalization rather than mere formatting, but it adds nothing about algo defaults or how prefixLen interacts with the returned short prefix.

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 first clause names a specific operation and resource: 'SHA-256/1/384/512 of a text body for cache keys and content addressing', so an agent immediately knows this is deterministic hashing, not encryption or a generic transform. It does not, however, distinguish itself from the sibling hash_encode, which plausibly overlaps in capability, leaving the agent to infer which one to pick.

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?

The description implies usage via 'for cache keys and content addressing', which gives a concrete intent, and the pricing line signals this is a metered external service. There is no explicit when-to-use versus when-not-to-use guidance and no mention of the sibling hash_encode as an alternative.

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