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

Annotations already establish readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description goes beyond that with genuinely non-obvious operational context: a 3-call-per-day free quota shared across all tools, then $0.001 USDC via x402 or card credits, paid in-band through params._meta["x402/payment"]. That payment mechanism is exactly the kind of thing an agent cannot learn from structured fields.

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, no filler, and the return-shape clause is a useful close. The main structural flaw is that the long pricing/payment sentence is front-loaded ahead of the actual purpose statement, delaying the agent's answer to "what does this do?" until sentence two.

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 an output schema present, the description needn't document return fields, and its one-line return summary is sufficient. Six optional parameters with zero schema descriptions leave gaps (no default or max for limit, no pagination behavior), but for a read-only search tool with clear filter names the coverage is largely adequate.

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 description coverage is 0%, so the description carries the full burden. It glosses keyword, category, language, scope, and official flag, but never mentions the limit parameter at all, nor explains that limit is typed as a string or that official only accepts "yes" — quirks an agent would otherwise get wrong.

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 gives a specific verb and resource ("Search 4,259 MCP (Model Context Protocol) servers") and enumerates the filterable dimensions, so the agent knows exactly what the tool returns. It does not, however, distinguish itself from the closely related siblings mcp_servers_sample and dump_mcp_servers, which is the only thing keeping it from a 5.

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?

Implicit guidance comes from the enumerated filters and the note that results include repo URL and description, which signals "use this to find a server." There is no explicit when-to-use/when-not statement and no routing to mcp_servers_sample or dump_mcp_servers, so the agent must infer which of the three MCP tools to pick.

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