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

Goes well beyond the readOnlyHint/openWorldHint annotations: it discloses the underlying dataset size (~1,200 active exit IPs), the enrichment source (Onionoo), the coverage limitation (only exit IPs, other relay IPs unchecked), and the cost model ($0.002 USDC per successful call via x402 on Base/Solana/Arc, failures free). Pricing and coverage caveats are exactly the behavioral facts structured fields cannot carry.

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 tight sentences: capability first, enrichment second, limitation third, cost last. Every sentence carries information the agent needs — none restates the tool name or the schema.

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-shape explanation is optional, yet the description still sketches what comes back when the IP is a hit. For a paid, single-parameter lookup, the combination of coverage scope, data source, and billing terms leaves nothing an agent needs missing before calling.

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% and the single 'ip' parameter is already documented with a format example, so the description adds nothing parameter-specific. Baseline 3 applies; the IPv4-only constraint is implied by the schema example rather than stated in the description.

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 and resource ('Checks an IPv4 address against the Tor Project's bulk exit list') and then names the enrichment source and the exact fields added (nickname, flags, country, first/last seen). This is clearly distinguishable from nearby siblings such as security_vpn_proxy_detector or security_abuseipdb_check without opening any schema.

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 scope statement 'Only exit IPs are on the list; a relay's other IPs are not checked' tells the agent the exact boundary of what this check answers, which is real usage context. However, it never names an alternative or says when to prefer a broader proxy/VPN detector instead, so routing decisions between siblings are left to inference.

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