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

With no annotations, the description carries real weight: it discloses the data source, refresh cadence (every 10 min), coverage start date, pay-per-call cost, USDC/Base payment rail, and that unpaid calls return a 402 challenge. That is meaningful behavioral context, though the return shape is not described.

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?

Three dense sentences that front-load what the tool returns, then add cadence and payment terms. Little waste, though the payment sentence is somewhat verbose relative to the core definition.

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 no-annotation, no-output-schema tool the payment and freshness disclosure is valuable, but the unexplained 'url' parameter and the phantom 'hours' parameter leave an agent unsure how to actually scope the query.

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 schema has a single required 'url' parameter with description merely 'required', which the description never explains. Worse, the description advertises a 'hours up to 2160' parameter that does not exist anywhere in the schema, creating confusion about how to control the time window.

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?

States a specific resource and scope: x402 endpoints whose price, asset or network changed recently. That clearly separates it from census_new (new endpoints) and census_search in the sibling list, though it doesn't name those siblings 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?

The 'changed recently' framing and the 'hours up to 2160' window imply when the tool applies, but there is no explicit guidance on when to choose this over census_new or census_search, nor any prerequisites for calling it.

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