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

With no annotations, the description carries the behavioral disclosure burden. It clearly discloses that the tool is paid, how payment works via x402 or a Bearer bby_live_... header, and that both path and query parameters go into params. However, it does not mention potential errors, response format, rate limits, or explicitly confirm read-only behavior beyond the word 'Fetch.'

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 compact, front-loaded with the core function, and every sentence adds necessary operational or pricing context. The standalone 'Paid.' immediately alerts the agent to the cost-bearing nature, and the subsequent sentences cover mechanics, alternatives, and payment methods without fluff.

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 generic endpoint-fetching tool with no output schema, the description covers the essential operational aspects: payment, authentication, parameter construction, and when to call describe_endpoint. It does not explain the response shape or error behavior, but the arbitrary endpoint nature makes a precise return contract impractical. Overall, an agent can call it correctly with the provided information.

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 100%, so the schema already documents both path and params thoroughly. The description adds some clarification by stating that path and query parameters are passed together in params, but this largely mirrors the schema's existing description. It is adequate but does not substantially elevate the semantics.

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 names a specific action and resource: 'Fetch live data from any fetcher.sh endpoint.' This clearly distinguishes fetch_data from sibling tools like describe_endpoint, search_endpoints, check_balance, and topup_credits. It also clarifies the generic scope versus the named per-endpoint MCP alternative.

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 gives practical guidance: call describe_endpoint first if unsure about parameters, use a named tool per endpoint when one exists, and expect a paid call. It does not explicitly enumerate when not to use fetch_data, but the routing to describe_endpoint and the named-tool alternative provides usable context.

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