Fixed-Size Chunking: Fast and Reliable

Why Fixed-Size?

Pros:

• ✅ Simple to implement
• ✅ Predictable chunk count
• ✅ Fast (no AI needed)
• ✅ Works for any content

Cons:

• ❌ Breaks sentences
• ❌ Ignores semantics

Basic Implementation

DEVELOPERpython
def fixed_chunk(text, chunk_size=500, overlap=50):
    chunks = []
    start = 0
    
    while start < len(text):
        end = start + chunk_size
        chunk = text[start:end]
        chunks.append(chunk)
        start += chunk_size - overlap  # Move forward with overlap
    
    return chunks

With Sentence Boundaries

Better: don't break mid-sentence:

DEVELOPERpython
import re

def chunk_by_tokens(text, chunk_size=500, overlap=50):
    # Split into sentences
    sentences = re.split(r'(?<=[.!?])\s+', text)
    
    chunks = []
    current_chunk = []
    current_size = 0
    
    for sentence in sentences:
        sentence_size = len(sentence)
        
        if current_size + sentence_size > chunk_size and current_chunk:
            # Save current chunk
            chunks.append(' '.join(current_chunk))
            
            # Start new chunk with overlap
            overlap_sentences = current_chunk[-2:] if len(current_chunk) > 1 else current_chunk
            current_chunk = overlap_sentences + [sentence]
            current_size = sum(len(s) for s in current_chunk)
        else:
            current_chunk.append(sentence)
            current_size += sentence_size
    
    if current_chunk:
        chunks.append(' '.join(current_chunk))
    
    return chunks

LangChain Implementation

DEVELOPERpython
from langchain.text_splitter import RecursiveCharacterTextSplitter

splitter = RecursiveCharacterTextSplitter(
    chunk_size=500,
    chunk_overlap=50,
    separators=["\n\n", "\n", ". ", " ", ""]
)

chunks = splitter.split_text(long_text)

Choosing Chunk Size

Small chunks (200-300):

• More precise retrieval
• But less context

Medium chunks (500-800):

• Balanced (recommended)

Large chunks (1000+):

• More context
• But noisy retrieval

Test on your data!

Fixed-size is battle-tested. Start here, optimize later if needed.