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by airano-ir
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

n8n: Update variable

n8n_update_variable
Destructive

Update an existing variable's value by site and key, enabling AI assistants to change stored configuration through MCP Hub. Requires an n8n Enterprise or Pro license.

Instructions

[UNIFIED] [Enterprise] Update an existing variable's value. Requires n8n Enterprise/Pro license.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "site": "<site>",
      "key": "<key>",
      "value": "<value>"
    },
    "name": "n8n_update_variable"
  }
}

Input Schema

NameRequiredDescriptionDefault
keyYes
siteYes
valueYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv3.14.0
  2. Removedv3.13.1
  3. First observedv3.4.0

TDQS

B3.1/5.0
Behavior3/5

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

Annotations already declare destructiveHint=true, idempotentHint=false, and readOnlyHint=false, so the safety profile is covered. The description adds a genuine behavioral fact beyond annotations — the Enterprise/Pro license entitlement requirement. It does not explain what overwriting the value destroys or why the operation is flagged non-idempotent despite setting a value.

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 short sentences, front-loaded with the operation and followed by the license constraint. The bracketed tags are terse metadata rather than wasted prose, though '[UNIFIED]' contributes little to an agent's decision.

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

Completeness2/5

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

For a destructive mutation with no output schema and zero parameter documentation, the description should explain the effect of overwriting, whether the key must already exist, and what 'site' scopes. It supplies only the license prerequisite, leaving most of what an agent needs before calling it unspecified.

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

Parameters2/5

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

Schema coverage is 0%, so all three parameters (site, key, value) are completely undocumented in the schema. The description only implies that 'value' is what gets replaced and that 'key' identifies the variable; the 'site' parameter — critical for a multi-site tool — receives no explanation anywhere.

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?

States a specific verb and resource ('Update an existing variable's value'), and the word 'existing' implicitly separates it from n8n_create_variable and n8n_get_variable. It does not explicitly name any sibling, but the operation is unambiguous.

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?

The Enterprise/Pro license prerequisite is useful context, and 'existing variable' implies the variable must already exist. However, there is no explicit guidance on when to use this versus n8n_create_variable (upsert behavior unclear) or on any other alternatives.

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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