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

With no annotations provided, the description fully bears the transparency burden. It discloses trial allowance limits, the signed receipt returned, the 402 response after allowance exhaustion, and that the tool reports rather than fabricates results. It also covers the payment parameter requirements. It could be more transparent about side effects or the contents of the receipt, but it is substantially informative.

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 two sentences: the first is a crisp statement of purpose, and the second packs trial and payment details into a dense but efficient format. Each clause contributes new information, though the second sentence is long and slightly run-on, which mildly hampers 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?

With 7 parameters, two nested objects, no output schema, and no annotations, the description covers the core behavior: how to invoke, the trial and paid flows, and error reporting on 402. It does not detail the exact structure of payment_authorization or the signed receipt, but the combination of description and schema gives a workable understanding of the tool.

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 input schema covers only 4 of 7 properties with descriptions (57% coverage). The three payment-related parameters (payment_channel, payment_channel_secret, payment_authorization) have no schema descriptions, but the description compensates by explaining their roles in paid and escrow access. It adds meaning beyond the schema, particularly for the undocumented parameters.

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 clearly states the tool's function: to 'Invoke a capability found via market_search.' The verb 'invoke' is specific and the resource is well-defined. It distinguishes itself from the sibling market_search by explicitly tying invocation to a prior search result, making its role unambiguous.

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 explains when to use the tool—after finding a capability via market_search. It also delineates the two access modes: trial invokes (no wallet, key, or channel) and paid access (payment_channel with secret, plus payment_authorization for escrow). However, it does not explicitly state when not to use it or mention exclusions, leaving a slight gap.

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