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

Annotations already declare readOnly/openWorld, and the description goes well beyond them: it discloses the pricing model ($0.002 USDC per successful call via x402 on Base/Solana/Arc, failed calls free), feed size (~300 active URLs, continuously updated), return shape (exact-URL and same-host match, feed size, up to 5 examples), and the false-negative caveat.

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?

Four sentences, each carrying distinct information: what it checks, what it returns, the reliability caveat, and the cost. The important caveat and pricing are front-loaded enough to be seen before invoking.

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, yet the description still summarizes the return contents, and it covers the non-obvious operational detail (paid x402 call, free on failure) that an agent must know before spending on a call. Nothing needed to invoke correctly is missing.

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 coverage is 100% and documents the single url parameter, so the schema carries the syntax burden. The description adds meaning beyond that by explaining the host-level matching behavior, which is not implied by the parameter definition alone.

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 verb (checks), resource (URL or host) and data source (OpenPhish public phishing feed), plus the exact matching semantics — exact URL or any URL on the same host. An agent can distinguish this from security_phishtank_check or security_urlhaus_malware by the named feed alone.

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?

Gives clear usage context: the feed is short and fast-changing, so 'not listed does not mean safe' — that tells the agent how to interpret a negative. It stops short of explicitly routing to a sibling (e.g. PhishTank or URLhaus) or naming when-not-to-use, so no exclusion guidance is present.

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