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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered; the description adds genuinely new context — that the call is free with no x402 payment challenge and returns no fact values, only metadata. The HTTP equivalent endpoint is a bonus for agents that can fall back to raw HTTP.

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?

Purpose and payload contents are front-loaded, which is good, but the payment message is stated twice ('FREE' in the opening and the full 'no payment required... this tool is free' clause), and the em-dash fragment plus HTTP endpoint add bulk. Trimming the duplicate free/payment note would make it tighter.

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 no output schema, the description carries the burden of describing the return payload, and it does so concretely (labels, counts, field names, op list, prices, freshness). Combined with annotations covering safety and zero parameters, an agent has nearly everything needed; only the relationship to sibling fact-bank tools is left implicit.

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 takes zero parameters, so there is nothing for the description to disambiguate at the argument level; baseline 4 applies. The schema is an empty object and the description correctly makes no parameter claims.

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 the resource (fact bank catalog) and enumerates exactly what it returns: stream labels, entity/fact counts, field names, op list, ruled prices, and store freshness. The line 'No fact values' usefully separates it from data-returning siblings such as fact_bank_status or fact_bank_tendency, though it never names a sibling explicitly.

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?

Usage is only implied: the emphasis on 'counts and labels only' and 'no payment required: call directly' suggests a free discovery/introspection call to run before fetching facts, but the description never states when to prefer this over fact_bank_status, fact_bank_health, or packs_catalog. The agent must infer the discovery-first pattern.

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