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

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. How to use it:

Click on a field that supports variable selection
Look for the variable picker icon or dropdown
Browse available outputs from previous nodes
Select the exact field you need

The output selector automatically generates the correct variable syntax for you, reducing errors and making configuration faster.

Understanding Variable Structure

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

{{node_name.output.property}}

Let’s break this down:

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

Real-world data often has nested structures. 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

When your data includes arrays, you can 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]}}

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.

Automatic Variable Updates

Let’s say you have a form trigger node named form1 being used in multiple places:

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

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

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

This happens automatically in:

Manual mode fields
AI Prompt mode instructions
Code node references
Condition node comparisons
All other node configurations

Best Practice: Name Nodes Meaningfully

Since renaming is seamless, invest time in giving nodes clear, descriptive names from the start: Good node names:

ExtractCustomerData
AnalyzeSentiment
SendWelcomeEmail
CheckInventoryStatus

Avoid generic names:

❌ agent1
❌ http_node
❌ trigger
❌ action

Reusing Variables Across Multiple Nodes

One of the most powerful features of variables is that you can use them multiple times across many different nodes. Once a node produces output, that data is available to all subsequent nodes in your workflow.

Basic Variable Reuse

Use the same variable in multiple nodes:

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

All three nodes can reference form1.output simultaneously since they all come after the trigger.

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}})

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

Use variables to filter or transform data: 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 };

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:

// Provide defaults in Code nodes
const email = trigger.output.email || "unknown@example.com";
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 by logging the variable
console.log(typeof trigger.output.amount);
console.log(JSON.stringify(trigger.output, null, 2));

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}}`	—

Best Practices

Use Descriptive Node Names

Name nodes clearly so variables are self-documenting: {{AnalyzeCustomerFeedback.output.sentiment}} is much clearer than {{agent1.output.sentiment}}

Test Variables After Each Node

After adding a node, run a test and click on the node to inspect its output. This confirms the data structure before using it in downstream nodes.

Provide Fallback Values

Use default values for optional fields:

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

Keep Variable Paths Simple

If you find yourself writing deeply nested paths like {{node.output.data.items[0].meta.tags[2].value}}, consider using a Code node to simplify the data structure first.

Document Complex Variable Usage

Add comments in Code nodes or descriptions in nodes when using complex variable logic, especially for team workflows.

Next Steps

Now that you understand variables, explore how to use them effectively in different contexts:

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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Troubleshooting

​Introduction

​Accessing Variables

​Method 1: Double Curly Braces ({{}})

​Method 2: Output Selector

​Understanding Variable Structure

​Accessing Nested Data

​Working with Arrays

​Complex Objects

​What Happens When You Rename Nodes

​Automatic Variable Updates

​Best Practice: Name Nodes Meaningfully

​Reusing Variables Across Multiple Nodes

​Basic Variable Reuse

​Use Case: Multi-Channel Notifications

​Advanced Variable Techniques

​Combining Multiple Variables

​Variables in Code Nodes

​Variables in AI Prompt Mode

​Filtering and Transformation

​Troubleshooting Variables

​Variable Not Available

​Undefined or Null Values

​Wrong Data Type

​Quick Reference

​Variable Syntax Cheat Sheet

​Best Practices

​Next Steps

Field Modes

Code Node

Condition Node

Core Concepts

Introduction

Accessing Variables

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

Method 2: Output Selector

Understanding Variable Structure

Accessing Nested Data

Working with Arrays

Complex Objects

What Happens When You Rename Nodes

Automatic Variable Updates

Best Practice: Name Nodes Meaningfully

Reusing Variables Across Multiple Nodes

Basic Variable Reuse

Use Case: Multi-Channel Notifications

Advanced Variable Techniques

Combining Multiple Variables

Variables in Code Nodes

Variables in AI Prompt Mode

Filtering and Transformation

Troubleshooting Variables

Variable Not Available

Undefined or Null Values

Wrong Data Type

Quick Reference

Variable Syntax Cheat Sheet

Best Practices

Next Steps