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

With no annotations, the description carries the burden and does well: it discloses the pre-registration upstream probe, failure on unreachable upstream, that registration does not spend funds, and the operator-key requirement. It omits duplicate-name behavior and what the response returns, leaving some gaps.

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?

Four tight sentences, front-loaded with the seller-side framing and the key behavior, with the operator-key requirement emphasized at the end. No sentence is wasted.

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 no output schema and no annotations, the description covers the core behavioral facts (probe, failure mode, no fund spend, auth). It falls slightly short on the nested-object parameters and duplicate-name/response semantics, but is largely sufficient to call 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 0% across 8 params, so the description must compensate. It gives real meaning to price_sats (per-request Lightning payment) and upstream_url (proxied target), but leaves upstream_headers, upstream_method, upstream_timeout_ms, category, and description unexplained.

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 ('put your HTTP endpoint behind an L402 paywall on our gateway') and frames it from the seller side, distinguishing it from gateway_list, gateway_update, and the buyer-side pay_l402_api. An agent can identify the operation without opening the schema.

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?

'Seller side' plus 'Registering does not spend funds' gives clear situational context and implicitly contrasts with spend tools like pay_l402_api. It states the operator-key requirement. It does not explicitly name an alternative (e.g., gateway_update for changes), so it stops short of full when/when-not guidance.

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