pfSense MCP Server

update_system_dns

Idempotent

Update pfSense system DNS settings by providing new server IPs, switching to local or remote resolution, and applying changes immediately.

Instructions

Update system DNS server settings

Input Schema

TableJSON Schema

Name	Required	Description
`dnsserver`	No	Array of DNS server IP addresses (e.g., ["8.8.8.8", "1.1.1.1"])
`dnslocalhost`	No	DNS resolution behavior — 'local' (use only the local resolver, 127.0.0.1) or 'remote' (use only the remote servers). Omit to leave the current behavior unchanged.
`apply_immediately`	No	Whether to apply changes immediately

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv1.1.0Sep 26, 2026

changedInput schema / properties / dnslocalhost / anyOf

Previous value: -[
-  {
-    "type": "boolean"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / properties / dnslocalhost / description

Previous value: -"Whether to use the local DNS resolver (Unbound) as the primary DNS"New value: +"DNS resolution behavior — 'local' (use only the local\nresolver, 127.0.0.1) or 'remote' (use only the remote servers).\nOmit to leave the current behavior unchanged."

First observedv1.0.0Aug 9, 2026

TDQS

C2.9/5.0

Behavior2/5

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

Annotations already indicate the operation is idempotent and non-destructive, but the description adds no behavioral context beyond the bare action. It does not mention that changing system DNS may affect DNS resolution or connectivity, nor does it clarify the practical effect of apply_immediately or whether changes require a restart.

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?

The description is a single, front-loaded sentence with no filler or redundancy. It is concise, though it sacrifices useful context that could have been added without much additional length.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Structured data covers the parameters, safety profile, and output schema, so the description does not need to re-explain those. However, for a system-level mutation tool, the description omits guidance on when to prefer it over similar DNS tools and does not note potential network-impact side effects, leaving the agent with only partial context.

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%, so the baseline is 3 even though the description itself adds nothing about parameters. The schema fully documents dnsserver, dnslocalhost, and apply_immediately, so the description does not need to compensate for missing parameter information.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb ('update') and a specific resource ('system DNS server settings'), making the core purpose clear. It is not a tautology, and it is distinguished from the read-oriented sibling get_system_dns, though it does not explicitly differentiate itself from update_dns_resolver_settings.

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

Usage Guidelines2/5

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

The description gives no guidance on when to use this tool versus alternatives like update_dns_resolver_settings, apply_dns_forwarder_changes, or get_system_dns. There are no conditions, exclusions, or hints about what distinguishes system DNS changes from other DNS-related operations.

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

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