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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds materially more: non-supported networks return 422, "Used also covers an authorization its signer cancelled," bad input is a 422 and not charged, latency is 1-3s, price is USD 0.002, and there is a free quota of 10 reads/IP/day. It also warns to treat returned text as untrusted data.

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 purpose and alternative before dense operational facts (error codes, timing, pricing, quota, security note). Every sentence earns its place, though the middle section is clause-heavy and could be split for readability.

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?

Given an output schema exists, return values need not be described. The description still covers network restrictions, error behavior, pricing/quota, latency, input selection, and a security caveat, leaving nothing an agent needs to invoke it correctly.

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 100%, so baseline is 3, but the description adds the key constraint the schema does not encode: network plus either x_payment or authorizer with nonce (and optional token). That XOR-style requirement is genuine semantic value beyond the schema, which only marks network required.

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 and resource with scope: "Check an x402 payment: was its USDC authorization used, can it still settle." It explicitly distinguishes itself from the sibling test_x402_payment, so an agent can route correctly without reading 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?

Names the alternative explicitly ("To make a real test payment instead use test_x402_payment") and gives the selecting condition. It also specifies when the tool applies (base/polygon/arbitrum only) and what input shapes are acceptable.

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