MyDevTools
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ASN Lookup

Find the network that announces one address, using a prefix table stored on this computer.

The lookup runs on your computer through the local agent. The address and the result stay on this page.

Local agent

Paste the current code from the agent window. The field is cleared after each attempt.

Agent disconnected

Set up the agent

Download and start the local agent, then come back to this page.

About the agent and download
  1. Start MyDevTools Agent.
  2. Copy the pairing code from the agent window.
  3. Paste the code below. If the browser asks for local-network access, allow it for this connection.

The browser sends the address only to the agent on 127.0.0.1. The agent looks it up in a prefix snapshot stored with the program and does not call a geo-IP service. It does not show a country or a city, and it does not resolve a hostname. The lookup is not part of path trace. This browser does not store the address or the result.

Address

One IPv4 or IPv6 address, or one CIDR. A name, a URL, a range and a list are not a query. The agent masks host bits and does not call a network API.

Result

Look up one address to see the announcing network.

On this page

ASN Lookup asks the local agent to match one address against a prefix snapshot stored on this computer. The grant is asn.lookup, separate from http.request, icmp.trace, dns.lookup, tcp.connect, tls.inspect and whois.lookup. The lookup does not call a geo-IP API.

Detailed Functionality

The snapshot is the iptoasn.com table from 2026-10-21, derived from RouteViews. The country column is not stored, and ASN 0 is omitted. A reserved, private or documentation address is a result, not an error. An address with no public prefix is reported as not found. One query is one address or one CIDR. The agent does not list more-specific prefixes inside a short query, and it does not add a column to path trace. At most two lookups run at once. This browser does not store the address or the result.

Practical Examples

  • 1.1.1.1 shows AS13335, CLOUDFLARENET and the prefix 1.1.1.0/24.
  • 8.8.8.8 shows AS15169 and GOOGLE.
  • 127.0.0.1 is reserved. No prefix is named.

How to Use This Tool

  1. Start the local agent

    Download the agent, start it, and copy the pairing code.

  2. Pair ASN lookup

    Paste the code and connect. The page asks for asn.lookup and keeps capabilities this browser already holds.

  3. Look up one address

    Enter one address or one CIDR and press Check.

  4. Read the network

    The page shows the status, the prefix, the ASN and the name. Copy it. Reloading the page clears the address and the result.

Tips and Best Practices

  • A reserved address and a missing prefix are results. They are not a failed lookup.
  • One request is one address or one CIDR. The agent does not scan a range and does not call a geo-IP API.
  • At most two lookups run at once.
  • The published Windows download may be older than this page. ASN lookup needs an agent that advertises asn.lookup.

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