SiteCheck Web Intel

Maps an IPv4 address to its origin AS number, the BGP

security_cymru_asn_lookup

Read-only

Maps an IPv4 address to its origin AS number, the BGP prefix that covers it, the country, the registry and the allocation date, using Team Cymru's public IP-to-ASN DNS service. Returns no origin when Cymru has no mapping for the address. Related tools on this server, for a different need: security_ip_geolocation_asn when you need IPv4 or IPv6 address → covering BGP prefix, origin; security_asn_peers_upstream when you need for an autonomous system: how many upstream and downstream. Price: $0.002 in USDC per successful call, paid with x402 (Base, Solana or Arc); failed calls are not charged.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "ip": "<ip>"
    },
    "name": "security_cymru_asn_lookup"
  }
}

Input Schema

Name	Required	Description	Default
`ip`	Yes	IPv4 address such as 8.8.8.8 (required)

Output Schema

Name	Required	Description	Default
`ip`	No
`asn`	No
`mapped`	No
`prefix`	No
`source`	No
`country`	No
`registry`	No
`allocated`	No
`checkedAt`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 23, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations only declare readOnlyHint and openWorldHint; the description adds real behavioral facts: no origin is returned when Cymru has no mapping, and each successful call costs $0.002 via x402 with failed calls not charged. That cost/charging semantics is exactly the kind of disclosure annotations cannot carry. It stops short of latency, rate limits, or caching behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core mapping, then the no-match caveat, then sibling routing, then pricing — each sentence carries distinct information. The pricing sentence is longer than the rest but is material to whether an agent should call at all.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a single-parameter read tool with an output schema, the description covers inputs, the return payload in prose, the empty-result case, sibling alternatives, and cost. Nothing an agent needs to decide whether and how to call is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With one parameter and 100% schema description coverage, the schema baseline applies, but the description still adds the meaningful constraint that the input must be IPv4 (the sibling handles IPv6). It does not say what happens if an IPv6 literal is passed, which is the one residual ambiguity.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource (maps an IPv4 address to origin AS, covering BGP prefix, country, registry, allocation date) and names the data source (Team Cymru IP-to-ASN DNS). The IPv4 scoping and the no-mapping case are both explicit, so an agent can distinguish this from security_ip_geolocation_asn or security_bgp_prefix_origin without opening a schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It explicitly routes to two alternatives with conditions: security_ip_geolocation_asn for IPv4/IPv6 prefix+origin and security_asn_peers_upstream for upstream/downstream counts. The routing against security_ip_geolocation_asn is weaker than it could be, since that sibling is described as returning the same prefix/origin data, leaving the actual selection rationale (IP version only) partly implicit.

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

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