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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false, so pure safety is covered. The description adds genuinely new behavioral context: the exact return payload (digest, input byte length, algorithm identifier) and the price/paid-over-x402 payment requirement, which the annotations do not capture.

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?

Dense but front-loaded: capability, algorithms, encodings, and returns come first, with pricing last. The enumeration of algorithms is long but earns its place by scoping the tool; little waste overall.

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?

Despite having no output schema, the description discloses the return shape (digest, byte length, algorithm identifier), input/output encodings, the HMAC option, and the payment model. Combined with annotations covering the safety profile, 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 the baseline is 3, but the description aggregates meaning across parameters: it explains default input encoding (UTF-8 text), the output encoding options, and that HMAC is computed 'with any of them'. This lightly exceeds what the schema fields convey individually.

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 ('compute a cryptographic digest of supplied data') and enumerates the exact algorithm family, distinguishing it clearly from siblings like geohash_encode_decode or solidity_function_selector. An agent immediately knows this is a hashing/HMAC utility.

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 nature of the tool, but there is no explicit 'use this when... instead of X' guidance. With no close sibling alternatives (geohash/selector are unrelated), the omission is low-cost, leaving this at the minimum-viable level.

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