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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so the safety profile is covered. The description adds genuinely new behavioral context not in annotations: a per-call price ($0.001 USDC via x402 on Solana) and a direct HTTPS endpoint — meaningful payment/auth details for an agent deciding whether to call.

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 definition and examples, then payment/endpoint details. Every sentence earns its place; the pricing and URL lines are the only additions beyond pure semantics, and they're operationally useful rather than padding.

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 single-parameter, read-only lookup with no output schema, the description is essentially complete: it defines the return value via examples, bounds the input, and discloses cost/access. Only sibling disambiguation is missing, which is minor given the strong examples.

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 carry the meaning of 'pos' — and it does, giving the valid range (1 to 999999999999) and worked examples that make the index semantics unambiguous. It stops short of edge-case behavior (e.g., pos=1) but is well above baseline for an undocumented param.

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 ('Which integer owns place pos in the Champernowne digit stream') and pins it down with three concrete examples (place 10/11 → 10, place 12 → 11, place 190 → 100). An agent knows exactly what the tool returns without opening the schema, though it doesn't explicitly name the point-sibling champernowne_digit.

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 via the examples; there is no explicit 'use this when / instead of champernowne_digit' guidance despite several closely related siblings (champernowne_digit, champernowne_place, champernowne_start, champernowne_len). An agent can infer the purpose but must reason about the alternative itself.

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