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

Beyond the minimal annotations (readOnlyHint=false, destructiveHint=false), the description discloses substantial behavior: it is a paid x402 operation, the first call returns a PaymentRequired, the second completes with a signed payment, and the receipt returns in _meta. It also explains the 'heartbeat' design rationale and the no-account/no-API-key requirement, giving full transparency about side effects and prerequisites.

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?

The description is longer than typical but front-loaded with the core purpose and payment model. The feedback-solicitation sentence at the end is somewhat tangential to invoking the tool, yet the overall structure flows logically from what → why → how, and every sentence earns its place.

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 paid multi-step tool with no output schema, the description covers the full workflow: price discovery, payment submission, receipt location, and auth requirements. It does not enumerate failure modes or edge cases, but the essential operational context is present and the complexity is well addressed.

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 schema already covers all three parameters with detailed descriptions, so the baseline is 3. The description adds a small amount of extra meaning by linking the 'plan' parameter to the pricing table via GET /pricing or service_card, but it does not materially enhance understanding of 'key' or 'holder' beyond the schema.

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 opens with a specific verb and resource: 'extend a hold you already have without losing your place in line'. It clearly distinguishes this from claim_acquire by stating that re-acquiring does NOT extend, so an agent can identify the exact operation and differentiate it from siblings.

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?

The description explicitly explains when to use this tool (extending an existing hold) and notes that claim_acquire deliberately does not extend, warning against using the wrong sibling for renewal. It also outlines the required two-step payment flow, so an agent knows exactly how to sequence calls.

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