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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely new behavioral facts: the exact response shape, the per-call price (1 credit = 1 CAD cent), and that schema-invalid input is rejected before billing. That billing/validation disclosure is real value beyond the annotations.

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?

Three sentences, each doing work: what is computed, what is returned, and what it costs. The return shape is front-loaded immediately after the purpose, with zero filler.

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 supplies the return object structure itself ({ algorithm, hex }) plus casing. Combined with the pricing and validation rules, an agent has everything needed to call it correctly and predict the cost.

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%, including the algorithm enum with its default and the 64,000-character limit, so both parameters are fully documented structurally. The description adds nothing beyond the schema about parameter syntax or edge cases (e.g., whether text is normalized). Baseline 3 applies.

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 specific verb (computes hex digest), the exact algorithms supported, the input encoding (UTF-8), and the return shape. This clearly separates it from siblings like base64 (encoding) or uuid (identifier generation). It stops short of naming an alternative sibling explicitly, so it lands at 4 rather than 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?

Usage is only implied by the tool's obvious function; there is no explicit 'use this when...' clause and no alternative tool is named for related tasks (e.g., base64 for reversible encoding). The billing note is an operational constraint, not selection guidance.

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