MAC Address Lookup

com.jasontally.macv1.0.0Updated Oct 2, 2026

Find the organization behind a MAC address or OUI prefix in the IEEE registries. No auth, no key.

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Overview

AI-generated overview

Looks up the organization behind a MAC address or OUI prefix using IEEE registry data.

What it does
Exposes one stateless tool, lookup, that takes a MAC address or OUI prefix and returns the registered organization, block type, address count, country, and a link to the record page. It matches full or partial addresses against IEEE MA-L, MA-M, MA-S, IAB, and CID assignments using longest-prefix precedence, and can flag randomized or virtual-machine ranges. The same data is also published as downloadable NDJSON files for clients that cannot speak MCP.
When to use it
Useful when an assistant needs to identify the vendor behind a MAC address or prefix, for example while reading ARP output, switch tables, or device logs. It is a small, single-purpose lookup service rather than a general networking toolkit.
Requirements
A remote Streamable HTTP endpoint at mac.jasontally.com/mcp. No account, API key, token, session, or handshake is required, and no environment variables or headers are declared. The assistant needs network access to that host.
Before you install
The endpoint is public and stateless, so no credentials are requested or presented. Lookups are sent to a third-party host; the README states the host serves static files and runs no search code, and that Cloudflare collects cookieless aggregate analytics. The tool only reads registry data and does not write, send, or delete anything.

Installation

In SourceWeft

  1. Open MAC Address Lookup in the dashboard and add it to a workspace.
  2. Enable the server for the chats that should use its tools.

Web executable via Streamable HTTP. Remote servers run from the web runtime once configured in a workspace.

Other MCP clients

Add this to your client's mcpServers config.

{
  "mcpServers": {
    "mcp": {
      "type": "http",
      "url": "https://mac.jasontally.com/mcp"
    }
  }
}

README

MAC Address Lookup

Free, fast, client-side MAC address vendor lookup. Paste a full or partial MAC address (OUI prefix, MA-M, MA-S, IAB, or CID block) and instantly identify the organization behind it — everything runs in your browser with no backend. We ask nothing of you: no ads, no cookies, no account, no tracking. The project came out of frustration with lookup pages wrapped in intrusive advertising: identifying a MAC vendor is a small utility, and it should be possible to build and host it for close to nothing.

mac.jasontally.com

The app does no tracking: there are no ads, no cookies, and every lookup runs in your browser, where the addresses you look up are never processed by a server. Normal requests still reach the host as with any website — a direct link such as /apple carries the term in its URL path, and the app fetches its public data files by URL — but the host only serves static files and runs no search code. The site is hosted on Cloudflare, which collects privacy-first, aggregate web analytics (Cloudflare Web Analytics) that use no cookies or client-side state and do not fingerprint individuals.

Features

  • Full or partial lookup — works with complete 48-bit addresses or just the leading hex digits (00:1A:2B, 001A2B3, 001A2B3C4)
  • Any format — colons, hyphens, Cisco dots, spaces, or plain hex; input is normalized automatically
  • Complete IEEE registry coverage — MA-L, MA-M, MA-S, IAB, and CID assignments, matched with longest-prefix precedence so small blocks resolve to the correct organization
  • Randomized MAC detection — flags locally administered / privacy-randomized addresses instead of returning a misleading "unknown vendor"
  • VM & hypervisor detection — recognizes VMware, VirtualBox, Hyper-V, KVM, Docker, Xen, and similar ranges
  • IEEE block details — assignment type, block size, address range, registered country, and organization details
  • Prefix lineage — for prefixes that changed hands (acquisitions, renames), a timeline of organizations and when each change was first observed. Shown only for the exact matched prefix, never inherited from parent or child blocks.
  • Paste anything — drop CLI output (arp -a, switch tables, logs) into the search box; every full MAC address inside is extracted and looked up, with non-address text ignored
  • Vendor and former-owner search — type a company name to list its prefixes; names from lineage match too ("Tekelec" finds the prefix that became Oracle), plus country names ("Germany"), registry types, and registration years
  • Registration dates and portfolios — first-registered dates for every prefix, and per-vendor block/address-space totals
  • Format conversions — see the address in every common notation
  • URL-driven lookups — no pasting required: mac.jasontally.com/001A2B renders the result directly. Batch lookups and vendor searches work the same way.
  • Static & private — the IEEE dataset loads in the browser; all searching, processing, and presentation happen locally, and the addresses you look up are never processed by a server. The app sets no cookies. The host (Cloudflare) collects privacy-first, cookieless, aggregate web analytics (Cloudflare Web Analytics).
  • Dark mode — follows your system preference by default, with a manual toggle
  • History, copy & share — recent lookups are stored locally; results are copyable and permalinked

URL-driven lookups

Navigate directly to a result — no form submission needed. Everything after / is the query (address, prefix, vendor/country/former-owner text):

URLResult
https://mac.jasontally.com/001A2BOUI / prefix lookup
https://mac.jasontally.com/001B213C4D5EFull address lookup
https://mac.jasontally.com/001A2B,005056Batch lookup (comma-separated, cap 250)
https://mac.jasontally.com/appleVendor search
https://mac.jasontally.com/tekelecFormer-owner search
https://mac.jasontally.com/vendorVendor index: every organization with two or more registered blocks
https://mac.jasontally.com/vendor/apple-incVendor page: every block registered to one organization
https://mac.jasontally.com/country/usCountry page: every organization with registered blocks
https://mac.jasontally.com/countryDimension index rollups: /country, /year, /region, /history, /successor (each is its own table over the corresponding page family)
https://mac.jasontally.com/former/apple-computerFormer-owner page: what happened to each renamed/reassigned block
https://mac.jasontally.com/?q=001A2BLegacy form (canonicalizes to /001A2B)

The page consumes the value from the URL path and displays the result without any manual input.

Pre-rendered pages

A build step pre-renders a real HTML page for every registered IEEE assignment — each OUI (MA-L), MA-M, MA-S, IAB, and CID prefix — so that people can find the tool when they look up a prefix or a vendor in their own words. Every page contains the vendor record without requiring JavaScript, and the interactive tool hydrates on top to resolve everything else in the browser: full addresses, partial prefixes, batch lists, vendor names, former owners, countries, and registration years. No brand is promoted as part of the app; the title is translated into local words for each language, because an English-only brand name would make it harder to find for everyone else. Generated pages include canonical URLs, schema.org metadata, sitemap.xml, and robots.txt. Sitemap: https://mac.jasontally.com/sitemap.xml.

On top of the prefix pages, the build generates vendor pages (/vendor/<slug>, every block registered to one organization — roughly 3,500 today), country pages (/country/<code>, every organization with blocks registered in a country — roughly 130), former-owner pages (/former/<slug>, roughly 350), and registry/year/region/history/successor dimension pages (/registry, /year, /region, /history, /successor), each family behind its own rollup index — /vendor (every organization with two or more blocks) and /country (every country) are both in the sitemap. The hub pages are complete static tables with no row caps, plus an internal relational link web: related-prefix sections (same vendor, adjacent prefixes, same registration year) on every prefix page, hub links from prefix pages, org directory links on country pages, and the home page's "MAC address by" nav reaching every rollup index. Rationale and capacity accounting: docs/thin-content-mitigation.md.

Data sources

  • IEEE Registration Authority — MA-L, MA-M, MA-S, IAB, and CID CSV registries (current assignments)
  • runZero mac-tracker — historical assignment changes back to ~1998, derived from IEEE snapshots and Wireshark/Ethereal archives (MIT)

Using the data from scripts, agents, and LLMs

  • llms.txt describes the site and data files for AI tools.
  • /.well-known/ai-catalog.json and /.well-known/ard.json are ARD 1.0 catalogs whose single entry describes the MCP server below. Real JSON at those paths also prevents the SPA fallback from serving HTML there.
  • Full download: data/registry.ndjson (~13.6 MB, one JSON object per IEEE assignment) and data/lineage.ndjson (ownership-change events). If your client cannot speak MCP, match the longest registered prefix against these yourself.
  • MCP server: /mcp is a stateless MCP server over Streamable HTTP. No key, no auth, no session, and no handshake required: a current client posts a request directly. It also answers an initialize probe statelessly, so a 2025-era client can connect too, and refuses an unsupported protocol version with -32022 listing what it does speak. One tool, lookup, takes a MAC address or OUI prefix and returns the registered organization, block type, address count, country, and a link to the record page in one call. Served by a Cloudflare Snippet (mcp/snippet.js, generated by build/mcp-shards.mjs); see docs/mcp-endpoint.md.
  • Auth discovery: /.well-known/oauth-protected-resource and /.well-known/oauth-protected-resource/mcp return RFC 9728 metadata naming no authorization server, because the endpoint is public and no token is ever presented.
  • Directory and registry listings: server.json at the repository root is the document the official MCP Registry publishes, and /.well-known/mcp/server-card.json is the same document at the path clients probe for pre-connection discovery (SEP-1649). test/mcp-listing.test.mjs keeps the two copies identical. Where the server can be listed, what each place checks, and the steps that need the account holder: docs/mcp-listing.md.
  • Load and correctness testing: npm run mcp:load drives the live endpoint with a real request mix and validates every response against a brute-force oracle built from registry.ndjson, so a fast wrong answer counts as a failure. See docs/mcp-endpoint.md → Load and correctness testing.

Tech stack

  • Static HTML/CSS/JavaScript — no backend at runtime; all lookup work happens in the browser
  • Single client bundle built with esbuild (engine + Hyparquet inlined): ~91 KB JS / ~18 KB CSS, gzip-served by Cloudflare
  • IEEE dataset stored as Apache Parquet and read in-browser with Hyparquet (pure JS, zero dependencies) — sharded by prefix so a lookup fetches a few KB instead of the full registry; no database or API
  • Pre-rendered prefix pages generated at build time so people can find the tool when they look up a prefix or a vendor — vendors, countries, former owners, and other registration dimensions get the same treatment (see above)
  • Deployed on Cloudflare Workers Static Assets (custom domain: mac.jasontally.com)
  • Architecture, platform constraints, and capacity planning: docs/architecture.md
  • Design language and UX requirements: docs/design.md

License

MIT

Source: README.md at commit e3ac30a

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Version history

1
  1. v1.0.0LatestOct 2, 2026