Fixing Langchain Go Markdown Splitter Chunking Issues

Introduction: The MarkdownTextSplitter Challenge

Markdown has become a ubiquitous format for writing and documentation due to its simplicity and readability. However, when dealing with large markdown documents, the need to split them into smaller, manageable chunks arises. This is where textsplitter tools, such as the NewMarkdownTextSplitter in the langchaingo library, come into play. The primary goal of a text splitter is to divide text into semantically meaningful chunks, ideally while preserving the original structure. In practice, getting the right balance between chunk size, structural integrity, and the number of chunks can be tricky. This article delves into a specific issue with the NewMarkdownTextSplitter, where it produces an unexpectedly large number of chunks and, crucially, alters the original markdown structure, especially with nested content like code blocks and lists. We will explore the expected behavior, the actual behavior, and provide a minimal, reproducible example to highlight the problem. By understanding these issues, developers can better utilize the NewMarkdownTextSplitter and improve the accuracy of their downstream language model applications.

The Problem Unveiled: Chunking and Structural Integrity

The central issue is that the NewMarkdownTextSplitter does not adhere to the specified chunk size, leading to an excessive number of smaller chunks. While the user configures a chunkSize, the actual chunks generated are significantly smaller than anticipated. This deviation from the expected behavior is further complicated by the fact that the splitter can corrupt the original Markdown structure. This is particularly noticeable when handling nested content like code blocks within lists or nested lists themselves. This means that important elements are separated, rendering the splitting process ineffective for preserving the meaning and context of the markdown. The core problem is that the splitter appears to break the text on every Markdown element rather than considering the configured chunkSize settings. This is a crucial aspect for any application processing markdown since preserving context is critical.

Expected Behavior vs. Actual Behavior: A Detailed Comparison

What We Anticipate: Chunk Size and Structure Preservation

When we configure the NewMarkdownTextSplitter, certain behaviors are expected. First, the chunks should be approximately the size specified by chunkSize. This could mean that, if we set the chunkSize to 500 tokens, each chunk should contain roughly 500 tokens. Of course, in practice, there will be variations, but they should be within reasonable bounds. The second expectation is the preservation of the markdown structure. This means lists should remain lists, headings should be separate headings, and code blocks should remain intact. This structural integrity is essential, especially when feeding the processed chunks to language models. For instance, a chunk of text that starts a code block should be split at the beginning of the code block. Finally, when advanced options like WithCodeBlocks(true) or WithJoinTableRows(true) are enabled, the chunks might exceed the specified chunkSize to keep code blocks and tables together. However, even with these exceptions, the splitter should still respect the chunkSize as much as possible.

The Reality: Deviations and Disruptions

Unfortunately, the actual behavior deviates significantly from what is expected. The NewMarkdownTextSplitter often generates far more chunks than it should. The produced chunks are often considerably smaller than the specified chunkSize. This behavior leads to inefficiency, increases processing overhead, and potentially reduces the quality of the results if it is used with other tools. Additionally, the text introducing code blocks, like the phrase