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TypeScript
Remote

Update split DNS (partial)

tailscale_update_split_dns
Idempotent

Update split DNS by merging only the specified domains, leaving all others unchanged. Set a domain to null to remove it.

Instructions

Partially update split DNS configuration. Merges the provided domains with the existing config -- only the specified domains are changed, others are untouched. To remove a domain, set it to null: that is the idiom the API reference documents. An empty array is also accepted and forwarded as-is -- it is what Tailscale's Terraform provider sends.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
splitDnsYesMap of domain to nameserver list to merge, or to null to remove that domain (e.g. { "new.example.com": ["10.0.0.3"], "old.example.com": null }). Only specified domains are changed.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed4 schema fields changedv0.21.0
    • addedInput schema / properties / splitDns / additionalProperties / anyOf
      Added value: +[
+  {
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  },
+  {
+    "type": "null"
+  }
+]
    • removedInput schema / properties / splitDns / additionalProperties / items
      Removed value: -{
-  "type": "string"
-}
    • removedInput schema / properties / splitDns / additionalProperties / type
      Removed value: -"array"
    • changedInput schema / properties / splitDns / description
      Previous value: -"Map of domain to nameserver list to merge (e.g. { \"new.example.com\": [\"10.0.0.3\"] }). Only specified domains are changed."New value: +"Map of domain to nameserver list to merge, or to null to remove that domain (e.g. { \"new.example.com\": [\"10.0.0.3\"], \"old.example.com\": null }). Only specified domains are changed."
  2. First observedv0.13.3

TDQS

A4.7/5.0
Behavior5/5

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

Annotations establish that this is a mutating, idempotent call, but the description adds the key behavioral details: it merges with existing config, only specified domains change, null removes a domain, and an empty array is forwarded as-is rather than interpreted as a clear operation. These details explain what changes and what does not, and they do not contradict the annotations.

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

Conciseness5/5

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

The description is three sentences, and each one earns its place: the first defines the operation and merge semantics, the second covers removal, and the third addresses the empty-array edge case. The core partial-update idea is front-loaded, and the Terraform-provider reference is a compact way to signal the intended semantics.

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?

For a single-parameter tool with thorough schema documentation and useful annotations, the description leaves no gap an agent needs to invoke it correctly. It states the operation, scope, merge behavior, removal semantics, and the empty-array edge case. The lack of an output schema is not a problem because invocation is fully specified.

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

Parameters4/5

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

The schema already documents the splitDns map, the null-to-remove idiom, and the fact that only specified domains change, so the baseline is solid. The description adds extra value by explaining that an empty array is accepted and forwarded as-is, which prevents misinterpretation. This goes beyond the schema's basic type constraints.

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?

The description opens with 'Partially update split DNS configuration', giving a specific verb, resource, and scope. It then explains the merge behavior ('only the specified domains are changed, others are untouched'), which clearly distinguishes it from full-replacement operations. The removal via null and empty-array handling make the tool's exact purpose unambiguous.

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

Usage Guidelines4/5

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

The description clearly conveys that this tool is for partial updates to split DNS, where only specified domains are merged into the existing config. It also documents the removal idiom (set to null) and the empty-array case. However, it does not explicitly point to set_split_dns as the alternative for full replacement, leaving the when-not contrast mostly implicit.

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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