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

Annotations already establish readOnly, idempotent, and non-destructive behavior, so the meaningful additions are 'No API key needed' and 'max 20 queries/session'. These are useful operational traits. However, the text mixes 'Price 0.01 USDC/query' with 'FREE preview — no key, no payment', creating ambiguity about whether a call actually costs money, and it does not describe what the response contains.

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 a promotional blurb rather than a structured tool specification. It repeats the 'no key / no payment / free preview' idea multiple times and buries the technical purpose under emojis, pricing, and sample questions. It is short, but not efficient for an agent to parse into actionable behavior.

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 tool with zero required parameters, it does communicate free/no-auth access and gives sample questions, which is helpful. However, it omits what the response looks like and how slug/question affect results, and the 'Price' vs 'FREE' statements are confusing. With no output schema, these gaps are more significant.

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 both parameters 100% with descriptions: slug defaults to the routed session's listing and question is echoed back. The sample questions add illustrative examples for the question parameter, but no extra semantics for slug are provided. With high schema coverage, the description does not need to repeat parameter details.

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 frames the tool as a 'FREE preview' of a 'New MCP Server Directory (Agent Tools Index)' and provides sample questions, so the general resource and action are inferable. However, it never explicitly states that the tool returns preview listing data for a slug/question, and it does not distinguish data_preview from siblings like data_session_query or discover_agents. The marketing tone obscures the operational meaning.

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 says 'No API key needed — call this now' and 'FREE preview — no key, no payment', which gives some sense of when calling is cheap or safe. But it provides no explicit guidance on when not to use this tool or which sibling tools should be used for full data access or session queries. The imperative 'call this now' is promotional rather than a decision rule.

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