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

Annotations already declare readOnly, idempotent, non-destructive, and openWorld, so the safety profile is covered. The description adds genuinely new behavioral context: a per-call price ($0.001 USDC via x402 on Solana) and a fallback HTTPS endpoint, which are things the annotations cannot express. It does not describe error handling for malformed permutations, so it falls just short of full transparency.

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 compact sentences plus a single endpoint line, with the core semantics front-loaded ahead of the pricing and transport details. Every sentence carries information, though the pricing and URL could arguably sit in a separate note rather than inline.

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 pure, read-only function with no output schema, the description covers semantics, validity constraints, cost, and an alternate transport. The only shortfall is that the return value is implied by the formula rather than stated as an array of length n, and input-validation failure behavior is unmentioned.

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?

With 0% schema description coverage, the description must carry the parameter meaning, and it does: it defines a and b as equal-length permutations over 0..n-1 and establishes their order of application. It does not restate the integer element type or the maxItems=10 bound, which the schema already constrains, so a small gap remains.

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 ('Compose') and resource ('two permutations of the same length') and states the exact index formula b[a[i]], which pins down the operation unambiguously. It is clearly distinguishable from siblings like perm_inverse, perm_rank, and perm_sign without opening their schemas.

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?

It specifies the composition order (a first, then b) and the preconditions ('Both must use 0..n-1 once each'), giving an agent the context needed to decide whether its inputs qualify. It stops short of naming alternatives such as perm_inverse or perm_next and does not say what to do on invalid input, so it is clear rather than exhaustive.

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