Value.Firewall

Remarks

This function is intended for internal use only and is not designed to be called directly in user-written M queries.

Value.Firewall is part of the Power Query data privacy firewall infrastructure. The firewall engine partitions data by source and enforces rules that prevent unauthorized data flow between sources with different privacy levels (e.g., Public, Organizational, Private). Value.Firewall retrieves a value from a specific firewall partition identified by the key parameter.

When Power Query evaluates a query that combines data from multiple sources, the engine internally inserts Value.Firewall calls to isolate data from each source into its own partition. This ensures that data from a Private source cannot leak into a query sent to a Public source, and vice versa.

### How the firewall works at a high level

• Each data source accessed in a query is assigned a privacy level (Public, Organizational, or Private).
• The engine creates partitions — one per data source — and wraps each partition's data behind Value.Firewall.
• Before combining data across partitions, the engine checks whether the combination is allowed by the configured privacy levels.
• If the combination violates the privacy rules, the query raises a Formula.Firewall error rather than silently leaking data.

You will typically encounter Value.Firewall only in diagnostic or trace output from the Power Query engine. Calling it directly will not produce useful results and may raise errors, since the key values are engine-internal identifiers.