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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully structured. The description adds value beyond those: it discloses that the call requires no API key, that it costs 0.01 USDC/query, and that a session is capped at 20 queries — practical constraints an agent needs before invoking. There is no contradiction with the annotations (the description's 'preview' matches the readOnly/idempotent hints).

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 reads as a user-facing marketing banner, not a tool spec: 'no key' and 'FREE' are repeated, 'call this now'/'Try one of the sample questions now' are imperative filler, and the actual purpose/location statements share space with price and sample-question copy. The actionable facts (price per query, session cap, guest accessibility) are present but packaged inefficiently; several sentences do not earn their place for an agent.

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 2 optional parameters, 0 required parameters, 100% schema coverage, and annotations covering safety, the description gives the agent enough to call it for free with cost/session limits. But with no output schema, the description never states what the call returns — the 'public metadata only' fact lives only in the input-schema description — leaving the agent to infer the response shape for a tool that has no output schema to document it.

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 100% — both 'slug' and 'question' are fully described in the schema, so the schema carries the semantic load and the baseline is 3. The description adds two concrete sample values for the 'question' parameter (e.g., 'What are the newest enterprise IT headlines?'), which is mild extra value, but it says nothing about 'slug' that the schema doesn't already cover.

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 conveys the basic verb+resource pair — a 'FREE preview' of the registerwatch listing — and even names the concrete listing/pricing, so an agent can tell it's a free trial of a specific plan. But the purpose is buried under promotional copy ('call this now', price, sample questions), and the description never states the core behavior that the schema supplies ('guest-callable taste of a listing — public metadata only') as text. It interacts with it implicitly, so the distinction from data_session_query is nicely skipped.

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?

'No API key needed — call this now' and 'FREE preview — no key, no payment' imply this is the guest entry point to try a listing before a paid/session call, and the 'max 20 queries/session' cap hints at scope. However, it never explicitly names alternative siblings like data_session_open or data_session_query or says when not to use this tool (e.g., when you need a paid full session), leaving the routing decision to inference.

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