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

With no annotations, the description carries the full burden. It discloses 'No authentication required' and 'Always returns 200', which are valuable behavioral facts. It also mentions 'Model-agnostic' and lists the return keys, providing transparency about the response shape. No contradictions with annotations exist.

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 well-structured with labeled sections ('WHEN TO USE', 'RETURNS') and is informative without excessive verbosity. The 'Model-agnostic' sentence is a slight extra but still adds relevant context. Overall, 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 zero-parameter read-only endpoint, the description is quite complete. It covers purpose, usage timing, authentication behavior, HTTP status, and return keys. The lack of an output schema is mitigated by the detailed explanation of the upgrade ladder. It could be more precise about the exact format of the response, but this is sufficient for an agent to use 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?

The tool has zero parameters, so the baseline is 4. The description does not need to add parameter semantics, but it does explain the return object structure and provides concrete examples (e.g., sandbox, x402, credits), which adds context beyond the empty 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 clearly states 'Returns available payment and authentication options for accessing live market data', which is a specific verb+resource. It distinguishes itself from siblings like get_market_schedule and list_exchanges by focusing on payment/authentication rather than market data itself.

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 provides 'WHEN TO USE: when you need to understand how to authenticate or pay before making a request that requires a key or payment.' This gives clear usage context, though it does not mention when not to use or explicitly name alternatives. Still, the siblings are clearly different, so this is strong guidance.

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