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

Annotations already declare readOnlyHint and destructiveHint=false, so 'reads or computes only and changes nothing' is largely redundant. The description does add genuinely useful behavior the annotations cannot convey: the payment model (x402 USDC or card key, first 25 free), that failed calls are free, and why repeats are not free — which explains idempotentHint=false.

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 core operation, algorithm options, and return formats are front-loaded in the first clause, with pricing and safety notes after. The billing detail is dense but operationally relevant; nothing is padding, though the parenthetical list of algorithms partly repeats the title.

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 correctly compensates by specifying that the digest is returned in both hex and base64. It leaves out any input size limits or error behavior for invalid algorithm values, which is a minor gap for a two-parameter tool.

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 baseline would be 3, but the description adds a real constraint not present in the schema: the input is treated as UTF-8 text. It also restates the default algorithm, which is mildly duplicative of the schema's 'sha256 (default)'.

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 names a specific verb and resource ('SHA256 hash of UTF-8 text') and enumerates the supported algorithms and both output encodings (hex, base64), so the agent knows exactly what comes back. It does not explicitly separate itself from the nearest siblings (hmac, pack_hash_toolbox), which keeps it below a 5.

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 for checksums, cache keys and deduplication' gives concrete usage contexts, which is more than most siblings offer. There are no when-not conditions or pointers to hmac for keyed hashing, so it stops short of full routing guidance.

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