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

Annotations already cover read-only, idempotent, non-destructive behavior. The description adds genuinely new context the agent needs before calling: a $0.001 USDC x402/Solana payment per successful call and an alternate HTTPS endpoint. It does not describe output structure explicitly, though the example implies 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 operation and a concrete example, then payment and endpoint details. Every sentence carries information, though the URL/pricing tail is metadata rather than math context.

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 effectively shows what comes back — squared length 30 and conjugate (1, -2, -3, -4) for input (1,2,3,4) — plus the cost and a transport alternative. A short note on output field naming would make it complete.

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 0%, so the description must compensate, and it does: the example '(1, 2, 3, 4)' shows the single `q` parameter is an ordered 4-tuple of numeric components. It still doesn't clarify that the schema expects strings rather than numbers, leaving a small ambiguity.

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 pair ('Conjugate and squared length of a quaternion') and cements it with a worked example, so it is distinguishable from siblings like quat_mul, quat_inv, and quat_pow. It does not explicitly name those siblings, so it falls short of 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?

'Unit means the squared length is 1' hints at the use case of checking normalization, but there is no explicit guidance on when to pick this over quat_inv or quat_pow, nor any stated preconditions. Usage is only implied.

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