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

With no annotations, the description carries the full behavioral disclosure burden. It adds valuable traits: 'Free, no key and no registration' and the price-based filtering behavior. It does not mention the return format or potential pagination, but for a simple catalog listing these omissions are minor. The disclosed traits go beyond what the empty schema provides.

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 sentences with no wasted words. The primary purpose is front-loaded, and the next-step guidance follows naturally. Every clause contributes value, from the scope ('every published service') to the cost/access statement ('Free, no key and no registration') to the routing to sibling tools.

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 zero-parameter, read-only catalog tool with no output schema, the description is complete. It tells the agent what it will get (services, descriptions, prices), the access requirements (none), and what to do after. No critical information needed to invoke or interpret the tool 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 tool has zero parameters, so per the rubric the baseline is 4. The description adds no parameter information because none exist. It correctly explains the output semantics (what services are listed) which is the only relevant semantic detail.

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: 'See what you can buy right now: every published service, what it does and its price'. It uses a specific verb ('see') and resource ('every published service'), and distinguishes itself from siblings by framing it as the starting point before creating a contract or paying per call. This leaves no ambiguity about what the tool does.

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?

Explicitly says 'Start here' and then directs the user to either marketplace_create_contract or marketplace_x402_payment for next steps. It also clarifies a key filter ('a service without a price is not listed'), which helps the agent know what to expect. This is strong when-to-use guidance with clear alternatives.

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