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

Annotations already mark readOnly, idempotent, non-destructive; the description adds concrete behavioral context beyond those annotations: public/zero-auth, 0 credits/AI calls, and the full list of no-op actions. No contradiction.

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?

Two tight sentences with no filler; the primary purpose is front-loaded and the second sentence adds only high-value constraints (cost, auth, and excluded side effects).

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 verification tool, the annotations, output schema, and parameter schema already carry the return and safety details; the description covers auth, cost, and side-effect exclusions. Nothing 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?

The parameter is fully documented in the schema (100% coverage), including the instruction to submit only compact receipt JSON and not Full Evidence JSON. The tool description itself adds only the word 'portable' about the parameter, so 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?

The description states a specific verb and object: 'public zero-auth MCP verification of a portable Nexus x402 Compact Audit Receipt.' It is not a tautology; it adds scope (public, portable, compact) and explicitly lists side-effecting actions it cannot perform, distinguishing it from the many trade/payment sibling tools.

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 gives clear context: use as a zero-auth, zero-cost read-only verification, and it enumerates what it cannot be used for (signing, paying, invoking buyers, contacting sellers, settling). It does not name an alternative tool explicitly, so it stops short of a 5.

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