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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description usefully adds that it checks public sources and returns limitations alongside evidence, plus concrete authentication/billing requirements (x402 v2 PAYMENT-SIGNATURE vs. Stripe headers), which is real behavioral context an agent needs before calling.

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: the purpose is front-loaded and the payment mechanics follow. The payment sentence is dense and acronym-heavy but every clause carries required operational information.

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?

An output schema exists, so return values need not be explained, and billing is covered. However, with four undocumented parameters, an enum-bearing response_mode, and no routing guidance against siblings, the definition is thinner than the tool's complexity warrants.

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% across four parameters (claim, source_urls, max_age_ms, response_mode), and the description explains none of them. The billing header names do not correspond to schema parameters, so the description does not compensate for the coverage gap at all.

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 states a specific verb and resource ('Check whether supplied public sources establish a claim') and names the return content ('evidence and limitations'). It is distinguishable from siblings like source_snapshot or web_qa, though it does not explicitly contrast itself with them.

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 guidance on when to use this tool versus siblings such as web_qa or source_watch_check, and no prerequisites beyond billing mechanics. The only usage instruction concerns payment, not task selection.

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