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: Types do not match! List =/= Single Value

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

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: Types do not match! Single Value =/= List

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

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: Types do not match! List of List =/= List

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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!

Custom Node BuilderList Size Mismatch Errors