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

Annotations already declare readOnly/destructive/openWorld/idempotent, so the bar is lower, yet the description adds real value: output encodings (hex and base64), the billing model ($0.003/call via x402 USDC or card key, first 25 free, failed calls free), and the clarification that repeats are charged. That last point explains the idempotentHint=false flag rather than merely restating it.

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 core action, then use cases, example, pricing, and a safety note — every sentence contributes something (function, relevance, format, cost, side effects). It is on the long side for a two-parameter utility but nothing is redundant.

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 compensates by specifying the return format (hex and base64), and it covers usage, cost, failure billing, and side-effect profile. Nothing material an agent needs to invoke it correctly is missing.

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; the description goes beyond it by restating the default algorithm and giving a concrete example (text=hello, algorithm=sha256) that shows the parameter relationship in practice. It doesn't document edge cases like unsupported algorithm errors, so it isn't a 5.

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?

Names a precise verb+resource (hash UTF-8 text) and enumerates the exact algorithm set (SHA-256 default, SHA-1, SHA-384, SHA-512), which also separates it from the sibling hmac (keyed) tool without naming it. An agent can identify exactly what this does from the first sentence.

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?

Gives concrete intended use cases ('checksums, cache keys and deduplication') and a worked example, so the when-to-use context is clear. It stops short of explicit exclusions or naming alternatives such as hmac or base64_encode, so it doesn't reach the top band.

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