Variable Usage

Introduction

Variables are the lifeblood of your workflows—they carry data between nodes, making your automations dynamic and context-aware. Every time a node completes execution, its output becomes available as a variable that subsequent nodes can access and use.

Think of variables as containers that hold data as it flows through your workflow. Understanding how to access and manipulate them is key to building powerful automations.

Accessing Variables

Langdock provides two intuitive ways to access variables from previous nodes in your workflow:

Method 1: Double Curly Braces ({{}})

The most direct way to reference variables is using the double curly brace syntax. Simply type {{ in any field, and you’ll see a dropdown of all available variables from previous nodes.

Basic syntax:

{{node_name.output.field_name}}

Real-world examples:

{{form1.output.email}}
{{analyze_feedback.output.sentiment}}
{{api_call.output.data.userId}}
{{trigger.output.customer_name}}

Method 2: Output Selector

Output Selector

For fields that support it, you can use the visual output selector instead of typing variable paths manually. This is especially helpful when you’re not sure of the exact data structure.

1

Click the field

Click on a field that supports variable selection.

2

Open the variable picker

Look for the variable picker icon or dropdown.

3

Browse outputs

Browse available outputs from previous nodes.

4

Select the field

Select the exact field you need — the output selector automatically generates the correct variable syntax for you.

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Understanding Variable Structure

Variables follow a consistent structure that makes them predictable and easy to work with:

{{node_name.output.property}}

Breakdown:

• node_name: The unique name you gave the node (e.g., form1, analyze_data, http_request)

• output: The standard output object every node produces

• property: The specific data field you want to access

Accessing Nested Data

You can access deeply nested properties using dot notation:

{{node_name.output.user.profile.email}}
{{api_response.output.data.items[0].title}}
{{trigger.output.metadata.created_at}}

Working with Arrays

Access specific elements by index:

{{http_request.output.results[0].name}}
{{trigger.output.attachments[2].url}}

Or reference the entire array:

{{trigger.output.tags}}
{{api_call.output.items}}

Complex Objects

For structured data from agents or API responses:

{{agent.output.structured.summary}}
{{agent.output.structured.priority}}
{{agent.output.structured.action_items[0]}}

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What Happens When You Rename Nodes

Node names are tied to variables. When you rename a node, all variables referencing that node are automatically updated throughout your workflow—no manual fixes needed.

Example: If form1 is used like this:

{{form1.output.email}}
{{form1.output.subject}}
{{form1.output.message}}

and you rename form1 to PMApplicantForm, all references update automatically:

{{PMApplicantForm.output.email}}
{{PMApplicantForm.output.subject}}
{{PMApplicantForm.output.message}}

This automatic update happens in:

• Manual mode fields

• AI Prompt mode instructions

• Code node references

• Condition node comparisons

• All other node configurations

Best Practice: Name Nodes Meaningfully

Good node names:

• ExtractCustomerData

• AnalyzeSentiment

• SendWelcomeEmail

• CheckInventoryStatus

Avoid generic names:

• ❌ agent1

• ❌ http_node

• ❌ trigger

• ❌ action

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Reusing Variables Across Multiple Nodes

Once a node produces output, that data is available to all subsequent nodes in your workflow.

Basic Variable Reuse

Example usage:

Trigger (form1) →
  ├─ Agent (analyze with {{form1.output.message}})
  ├─ HTTP Request (log {{form1.output.email}})
  └─ Notification (alert about {{form1.output.priority}})

Use Case: Multi-Channel Notifications

Send the same information through different channels:

Agent (analyze_ticket) →
  ├─ Email (send {{analyze_ticket.output.summary}} to support team)
  ├─ Slack (post {{analyze_ticket.output.summary}} to #support)
  └─ Database (log {{analyze_ticket.output.priority}} and {{analyze_ticket.output.category}})

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Advanced Variable Techniques

Combining Multiple Variables

Mix data from different nodes in a single field:

New order #{{trigger.output.order_id}} from {{customer_data.output.name}} for {{trigger.output.amount}}

Variables in Code Nodes

Access variables as standard objects in code nodes.

JavaScript:

const email = trigger.output.email;
const priority = analyze.output.structured.priority;
const score = calculate_score(email, priority);

return { score: score, email: email };

Python:

email = trigger["output"]["email"]
priority = analyze["output"]["structured"]["priority"]
score = calculate_score(email, priority)

return {"score": score, "email": email}

Variables in AI Prompt Mode

Reference multiple variables in AI instructions:

Analyze the customer message {{trigger.output.message}} and consider their history:
- Previous purchases: {{customer_data.output.purchase_count}}
- Last contact: {{customer_data.output.last_contact_date}}
- Sentiment from last interaction: {{previous_analysis.output.sentiment}}

Provide a personalized response addressing their concern.

Filtering and Transformation

In a Condition node:

{{trigger.output.amount}} > 1000
{{analyze.output.priority}} == "high"
{{customer.output.status}} != "inactive"

In a Code node for filtering:

const orders = trigger.output.orders;
const highValueOrders = orders.filter((order) => order.amount > 1000);

return { filtered_orders: highValueOrders };

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Troubleshooting Variables

Variable Not Available

Problem: The variable you want doesn’t appear in the autocomplete.

Common causes:

• The node hasn’t been connected yet

• The node is downstream (comes after) the current node

• The node hasn’t been executed in a test run yet

Solution: Ensure the node producing the variable comes before the node trying to use it in your workflow graph.

Undefined or Null Values

Problem: Variable exists but returns undefined or null.

Common causes:

• The source node failed or returned empty data

• The field path is incorrect

• Optional data wasn’t provided

Solution examples:

// Provide defaults in Code nodes
const email = trigger.output.email || "[email protected]";
const amount = trigger.output.amount || 0;

// Check existence first
if (trigger.output && trigger.output.email) {
  // Safe to use
}

Wrong Data Type

Problem: Variable contains unexpected data type.

Solution: Check the output tab of the source node after a test run to see the actual data structure.

Debug example:

// Debug by logging the variable
console.log(typeof trigger.output.amount);
console.log(JSON.stringify(trigger.output, null, 2));

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Quick Reference

Variable Syntax Cheat Sheet

Use Case	Syntax	Example
Basic field access	{{node.output.field}}	{{trigger.output.email}}
Nested object	{{node.output.object.property}}	{{user.output.profile.age}}
Array element	{{node.output.array[index]}}	{{items.output.list[0]}}
Nested in array	{{node.output.array[0].property}}	{{orders.output.items[0].price}}
Entire array	{{node.output.array}}	{{trigger.output.tags}}
Agent structured output	{{agent.output.structured.field}}	{{analyze.output.structured.summary}}
Multiple in one string	Order {{trigger.output.id}} for {{trigger.output.amount}}	—

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Best Practices

• Use Descriptive Node Names — e.g., {{AnalyzeCustomerFeedback.output.sentiment}} is clearer than {{agent1.output.sentiment}}

• Test Variables After Each Node — run a test and inspect node output to confirm structure

• Provide Fallback Values — e.g.:

  const priority = analyze.output.priority || "medium";
  const tags = trigger.output.tags || [];

• Keep Variable Paths Simple — consider a Code node to simplify deeply nested data

• Document Complex Variable Usage — add comments in Code nodes or descriptions in nodes for complex logic

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Next Steps

Explore these related topics:

• Field Modes — Learn how to use variables in Auto, Manual, and AI Prompt modes

• Code Node — Transform and manipulate variables with custom code

• Condition Node — Use variables to create dynamic routing logic

• Core Concepts — Understand how variables fit into the bigger picture

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Output Selector