Microsoft Tenant ID lookup

Where tenant IDs are used

• Entra ID app registrations and single sign-on set-ups.
• Cross-tenant access settings and B2B collaboration between organisations.
• PowerShell and Microsoft Graph connections to a specific tenant.
• Partner and MSP access (GDAP), and Microsoft support cases.

Is a tenant ID secret?

No. Microsoft publishes it in the tenant’s public sign-in configuration, so anyone can find it for a domain that uses Microsoft 365. On its own it gives no access to anything. It does reveal that a domain uses Microsoft 365, which is worth keeping in mind for phishing awareness — attackers use the same lookup.

Reverse lookup (tenant ID to domain)

Microsoft has no anonymous way to turn a tenant ID back into a domain, so the reverse lookup goes through Microsoft Graph. It returns the organisation’s display name and default domain where Microsoft makes them available; for some tenants no result is returned.