Type mismatch errors occur when you try to connect nodes with incompatible data types. Don’t worry though - they’re easy to understand and fix once you know what to look for! This guide will help you identify these errors and show you exactly how to resolve them.

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What is a Type Mismatch Error?

A type mismatch error occurs when you try to connect nodes that expect different types of data. In Gumloop, data flows between nodes in two main formats:
  • Text (String): A single piece of information (one email, one article, one message)
  • List (Array): Multiple pieces of information (multiple emails, articles, messages)
The basic rule is simple:
  • If a node expects text input → pass in text
  • If a node expects list input → pass in list
However, there’s a special case: You can pass a list into a node that expects text by enabling “Loop Mode”. When Loop Mode is on, the node will process each item in the list one by one. For example:
A type mismatch typically happens when you try to:
  1. Send a list where a node expects a single text Example: Trying to send [email1, email2, email3] to a node that expects just one email
  2. Send a single text where a node expects a list Example: Trying to send one email to a node that expects [email1, email2, email3]
When this happens, you’ll see a red error message warning you about the mismatch. The good news is that these errors are easy to fix using the right nodes, which we’ll cover in this guide.

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Common Scenarios and Solutions

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Scenario 1: List → Text (Multiple Items to Single Item)

The Problem: You have a list of items (like multiple research topics from a Google Sheet) that you want to process as a single text input (like merging them and sending as a single message on Slack). Example:
Error Message: Single Value Expected, List Received
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The Solution: Use the Join List Items node to combine all items in the list into a single text string. Steps:
  1. Insert a Join List Items node between your nodes
  2. Connect your list output to the Join List Items input
  3. Choose a separator (like newline)
  4. Connect the Join List Items output to your target node
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Common Use Case:
  • Combining any list of items into a single text
  • Converting any list data into a single text string for nodes that expect text input
  • Processing multiple items together rather than individually in a loop

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Scenario 2: Text → List (Single Item to Multiple Items)

The Problem: You have a single text item (like a writing style guide from a Google Doc) that needs to be used with each item in a list (like multiple blog posts that need the same style guide). Example:
Error Message: List Expected, Single Value Received
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The Solution: Use the Duplicate node to create a list containing multiple copies of your text. Steps:
  1. Add a Duplicate node after your single text source
  2. Connect your text to the Duplicate node’s input
  3. Connect your list to the “List size to match” input
    • This tells the node how many copies to create
  4. The output will be a list of identical items matching your other list’s size
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Common Use Case:
  • Using any single text input with multiple list items
  • Applying the same data or context across multiple operations
  • Converting any single text input into a list to match other list operations

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Scenario 3: List of Lists → List (Nested Lists)

The Problem: You have a nested list (a list containing other lists) but need a simple, flat list. Example:
Error Message: List Expected, List of List Received
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Two Solutions:

  1. Create a subflow to process each inner list
  2. Add input/output nodes in the subflow
  3. Process the inner list items individually
  4. Use the subflow in your main flow with Loop Mode enabled
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Option 2: Use Flatten List Node

  1. Add the Flatten List node
  2. Connect your nested list to it
  3. Get a single-level list as output
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Tips for Preventing Type Mismatches

  1. Check Node Types:
    • Look for list vs text indicators in the node input and output connections
  2. Understanding Loop Mode:
    • Enable for processing lists item by item
    • Disable when working with entire lists at once
    Example: If you have a Google Sheet with a column that you want to send to AI as a whole for context, you’d use a Join List Items node to merge the contents of each row from that column instead of enabling loop mode and processing each row in a loop.
  3. Plan Your Data Flow:
    • Think about whether you need to process items individuall in a loop or as a group
    • Consider using Join List Items when you need all items processed together without looping over each item
    • Use Loop Mode when each item needs individual processing

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Quick Reference Table

ScenarioProblemSolution NodeHow It Works
List → TextNeed to combine multiple items into oneJoin List ItemsConcatenates all items in a list into a single text string, using a separator
Text → ListNeed to use one item with manyDuplicateCreates multiple copies of a single text input to match the size of another list, ensuring compatible data structures
List of Lists → ListHave nested lists that need flatteningSubflow or Flatten ListEither processes inner lists through a dedicated flow (Subflow) or combines all nested items into a single-level list (Flatten List)
Still stuck? If you’ve tried these solutions and still can’t resolve your type mismatch error, reach out on forum.gumloop.com and we’ll help!