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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false), so the bar is lower; the description adds real value beyond them by disclosing pricing ($0.01/call via x402 USDC or card key), 25 free calls, and that failed calls are free. 'Each call is charged, so repeats are not free' usefully explains the non-idempotent annotation in practical terms, though 'reads or computes only' merely restates the readOnly hint.

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?

Core capability, usage, and cost are front-loaded in a compact four-sentence block with no filler. Minor redundancy: the per-call price and the 'repeats are not free' sentence say much the same thing.

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?

For a two-parameter, no-output-schema tool, the description supplies everything needed: algorithms, default, input encoding, and return formats (hex and base64). An agent can call this correctly without opening the schema.

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 both parameters are already documented, and the description adds only a default restatement (SHA-256 default) and one example (text=hello). That is marginal added meaning over the structured schema, which is the expected baseline 3 case.

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 gives a specific verb (hash), resource (UTF-8 text), supported algorithms with an explicit default, and the return encoding (hex and base64). It is highly self-describing, but it never distinguishes itself from close siblings like hmac or pack_hash_toolbox, leaving the agent to infer that this tool is unkeyed hashing.

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 rather than vague intent. It stops short of stating when NOT to use it — e.g. use hmac for keyed digests, or another tool for file hashing — so there is no explicit alternative routing.

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