MAC Address Lookup

Look up a MAC address or OUI prefix

lookup

Read-onlyIdempotent

Resolve a MAC address or OUI prefix to its registered organization using longest-prefix match across the MA-L, MA-M, MA-S, IAB, and CID registries. Reports the block type, address count, registration country, and a link to the full record page. Randomized and locally administered addresses usually have no registered organization.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`mac`	Yes	MAC address or OUI prefix, 6 to 12 hex characters. Accepts colon, hyphen, Cisco dot, or plain hex, for example 8C:1F:64:AF:A4:B2 or 8C1F64.

Output Schema

TableJSON Schema

Name	Required	Description
`url`	Yes	Record page on https://mac.jasontally.com.
`query`	Yes	The normalized query, colon-separated.
`prefix`	Yes	Longest registered prefix that matched.
`country`	No	ISO 3166-1 alpha-2 registration country.
`orgName`	No	Registered organization name.
`blockType`	No	MA-L, MA-M, MA-S, IAB, or CID.
`multicast`	No	The bit pattern marks the address a multicast group.
`addressCount`	No	Addresses in the matched block.
`locallyAdministered`	No	The bit pattern marks the address locally administered, which usually means a randomized or virtual-machine address.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 5, 2026

changedOutput schema / properties / locallyAdministered / description

Previous value: -"The bit pattern marks the address locally administered, which usually means a randomized or virtual-machine address. Present only when there is no match."New value: +"The bit pattern marks the address locally administered, which usually means a randomized or virtual-machine address."

changedOutput schema / properties / multicast / description

Previous value: -"The bit pattern marks the address a multicast group. Present only when there is no match."New value: +"The bit pattern marks the address a multicast group."

Changed2 schema fields changedOct 2, 2026

addedOutput schema / properties / locallyAdministered

Added value: +{
+  "description": "The bit pattern marks the address locally administered, which usually means a randomized or virtual-machine address. Present only when there is no match.",
+  "type": "boolean"
+}

addedOutput schema / properties / multicast

Added value: +{
+  "description": "The bit pattern marks the address a multicast group. Present only when there is no match.",
+  "type": "boolean"
+}

First observedOct 2, 2026

TDQS

A4/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is covered. The description adds real value beyond that: the longest-prefix matching algorithm, the specific registries searched, the fields reported, and the failure mode for randomized/LAA addresses.

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

Conciseness4/5

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

Two tightly written sentences with the core operation front-loaded and the edge-case caveat last. The middle sentence enumerating reported fields is mildly redundant given an output schema exists, but it aids scanning and does not bloat the text.

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?

An output schema exists so return values need not be explained, and annotations cover the safety profile. The description still supplies everything an agent needs: input domain, resolution semantics, source registries, and the important caveat about unresolvable address classes.

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

Parameters3/5

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

Schema description coverage is 100% and the schema already documents accepted lengths (6-12 hex chars) and all four accepted formats with an example. The description only echoes 'MAC address or OUI prefix' without adding format or normalization detail, so the baseline 3 applies.

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 ('Resolve a MAC address or OUI prefix to its registered organization') and names the exact registries consulted (MA-L, MA-M, MA-S, IAB, CID), so the agent knows precisely what operation is performed. With no siblings, no differentiation is needed.

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

Usage Guidelines3/5

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

There are no siblings to route against, so alternatives are moot, but the description never states explicitly when to use the tool versus other resolution paths. The note that randomized/locally administered addresses usually have no registered organization is a useful expectation-setting hint that partially compensates.

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

All MAC Address Lookup tools Inspect

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