ValueError
builtins.ValueError
Stack trace
ValueError: overlap tokens cannot be greater than chunk size
File "/app/my_script.py", line 42, in split_text
raise ValueError("overlap tokens cannot be greater than chunk size") Why it happens
When splitting text into chunks for context windows, the overlap parameter must be smaller than the chunk size. If overlap tokens exceed or equal the chunk size, the splitter cannot create valid chunks, triggering this error.
Detection
Validate chunk size and overlap parameters before splitting text; assert that overlap < chunk size to catch misconfiguration early.
Causes & fixes
Overlap tokens parameter is set equal to or larger than the chunk size.
Reduce the overlap tokens value to be strictly less than the chunk size in your text splitter configuration.
Dynamic chunk size or overlap values computed incorrectly, causing overlap to exceed chunk size at runtime.
Add validation checks after computing chunk size and overlap to ensure overlap < chunk size before passing to the splitter.
Using default or hardcoded values without verifying their relationship, leading to invalid overlap settings.
Explicitly set and verify chunk size and overlap parameters in your code, avoiding defaults that violate the constraint.
Code: broken vs fixed
from langchain.text_splitter import RecursiveCharacterTextSplitter
text_splitter = RecursiveCharacterTextSplitter(chunk_size=100, chunk_overlap=150) # overlap > chunk_size
chunks = text_splitter.split_text(long_text) # Raises ValueError hereimport os
from langchain.text_splitter import RecursiveCharacterTextSplitter
# Fixed: overlap less than chunk size
text_splitter = RecursiveCharacterTextSplitter(chunk_size=100, chunk_overlap=50) # overlap < chunk_size
chunks = text_splitter.split_text(long_text)
print(f"Split into {len(chunks)} chunks successfully.")Workaround
Wrap the splitter call in try/except ValueError, catch the error, and programmatically adjust overlap to chunk_size - 1 before retrying the split.
Prevention
Implement parameter validation in your text splitting utility to enforce overlap < chunk size, and use unit tests to catch invalid configurations before deployment.