API reference

All signatures on this page are verified against the current @exulu/backend source. For option details, see Configuration.

Namespace import

import { ExuluChunkers, defaultChunker } from "@exulu/backend";
import type { ChunkerOperation, ChunkerResponse } from "@exulu/backend";

ExuluChunkers.sentence            // SentenceChunker class
ExuluChunkers.markdown            // MarkdownChunker class (Enterprise Edition)
ExuluChunkers.recursive.function  // RecursiveChunker class
ExuluChunkers.recursive.rules     // RecursiveRules class

SentenceChunker

SentenceChunker.create()

Static async factory. The constructor is private.

SentenceChunker.create(options?: SentenceChunkerOptions): Promise<CallableSentenceChunker>

Returns a CallableSentenceChunker — an object that is both callable and has class properties/methods.

interface SentenceChunkerOptions {
  tokenizer?: TokenizerModelName;         // default "gpt-3.5-turbo"
  chunkSize?: number;                     // default 512
  chunkOverlap?: number;                  // default 0; must be < chunkSize
  minSentencesPerChunk?: number;          // default 1
  minCharactersPerSentence?: number;      // default 12
  approximate?: boolean;                  // deprecated; no effect
  delim?: string[];                       // default [". ", "! ", "? ", "\n"]
  includeDelim?: "prev" | "next" | null;  // default "prev"
}

Calling the chunker

// Single text
const chunks: SentenceChunk[] = await chunker(text: string, showProgress?: boolean);

// Batch
const batchChunks: SentenceChunk[][] = await chunker(texts: string[], showProgress?: boolean);

SentenceChunk properties

type SentenceChunk = {
  text: string;
  startIndex: number;  // Byte offset in the original text
  endIndex: number;
  tokenCount: number;  // Accurate token count via ExuluTokenizer
  sentences: Sentence[]; // Individual sentences in this chunk
};

chunk()

Chunk a single text string. Called internally when the chunker is invoked as a function.

chunker.chunk(text: string): Promise<SentenceChunk[]>

Properties

After create(), these are available on the instance:

Property	Type	Notes
`chunkSize`	`number`	Effective max tokens per chunk
`chunkOverlap`	`number`	Token overlap between consecutive chunks
`minSentencesPerChunk`	`number`	Minimum sentences guaranteed per chunk
`minCharactersPerSentence`	`number`	Minimum sentence length before merging
`delim`	`string[]`	Active sentence delimiters
`includeDelim`	`"prev" \| "next" \| null`	Delimiter placement
`tokenizer`	`ExuluTokenizer`	The tokenizer instance

RecursiveChunker

RecursiveChunker.create()

Static async factory. The constructor is private.

RecursiveChunker.create(options?: RecursiveChunkerOptions): Promise<CallableRecursiveChunker>

interface RecursiveChunkerOptions {
  tokenizer?: TokenizerModelName;        // default "gpt-3.5-turbo"
  chunkSize?: number;                    // default 512
  rules?: RecursiveRules;               // default new RecursiveRules()
  minCharactersPerChunk?: number;        // default 24
  prefix?: string;                       // prepended to every chunk
  retainHeaders?: boolean;               // default false
}

Calling the chunker

// Single text
const chunks: RecursiveChunk[] = await chunker(text: string, showProgress?: boolean);

// Batch
const batchChunks: RecursiveChunk[][] = await chunker(texts: string[], showProgress?: boolean);

RecursiveChunk properties

type RecursiveChunk = {
  text: string;       // Chunk text (prefix prepended if set)
  startIndex: number;
  endIndex: number;
  tokenCount: number;
  level: number;      // Recursion level where the split occurred; 0 = top level
};

chunk()

chunker.chunk(text: string): Promise<RecursiveChunk[]>

Properties

Property	Type	Notes
`chunkSize`	`number`	Effective max per chunk (adjusted for prefix)
`minCharactersPerChunk`	`number`	Minimum character count per chunk
`rules`	`RecursiveRules`	Active rule set
`prefix`	`string \| undefined`	Prefix prepended to each chunk
`prefixTokenCount`	`number`	Token count of the prefix (0 if none)
`retainHeaders`	`boolean`	Whether header context is prepended

RecursiveRules

import { ExuluChunkers } from "@exulu/backend";

const rules = new ExuluChunkers.recursive.rules({ levels? });

interface RecursiveLevelData {
  delimiters?: string | string[];
  whitespace?: boolean;
  includeDelim?: "prev" | "next";  // default "prev"
}

Constructor

RecursiveLevelData[]

Array of level definitions. When omitted, the five built-in levels are used (paragraphs → sentences → punctuation → words → tokens).

whitespace and delimiters are mutually exclusive on a single level — passing both throws.

Properties and methods

Member	Type	Notes
`levels`	`RecursiveLevel[]`	Ordered array of level objects
`length`	`number`	Number of levels
`getLevel(index)`	`RecursiveLevel \| undefined`	Level at the given index
`RecursiveRules.fromDict(data)`	`RecursiveRules`	Static factory from a plain object

MarkdownChunker

Enterprise Edition class. Instantiate directly:

import { ExuluChunkers } from "@exulu/backend";

const mdChunker = new ExuluChunkers.markdown();

chunk()

mdChunker.chunk(
  text: string,
  chunkSize: number,
  prefix?: string,
  config?: { pageBreakTags?: boolean },
): Promise<{ text: string; page: number }[]>

string

required

The markdown text. Tables are converted to numbered-list format; <page_break page=N> tags are tracked for page numbering.

number

required

Target max tokens per chunk (effective budget is reduced by prefix and active header context tokens).

string

Optional string prepended to every chunk. Token count subtracted from the effective budget.

boolean

default:"false"

Prepend  to each chunk.

string

Full chunk content: optional page comment + header context (for non-current headers) + optional prefix + slice of the document.

number

Page number (1-based) in effect at the chunk boundary. Always 1 when no <page_break> tags are present.

convertTablesToText()

Converts markdown tables in a string to numbered-list format and returns the result. Called automatically by chunk().

mdChunker.convertTablesToText(text: string): string

Useful for pre-processing content before passing it to another chunker.

ChunkerOperation and ChunkerResponse

These are the types that connect chunkers to ExuluContext.

import type { ChunkerOperation, ChunkerResponse } from "@exulu/backend";

type ChunkerOperation = (
  item: Item & { id: string },
  maxChunkSize: number,
  utils: { storage: ExuluStorage },
) => Promise<ChunkerResponse>;

type ChunkerResponse = {
  item: Item & { id: string };
  chunks: {
    content: string;
    index: number;
    metadata?: Record<string, unknown>;
  }[];
};

ChunkerOperation parameters

Item & { id: string }

required

The fully hydrated item record. Includes id, name, content, description, and all custom fields defined in the context schema.

number

required

The token budget per chunk, derived from the embedder model’s max_chunk_size as reported by LiteLLM. Pass this directly to the underlying chunker’s chunkSize option.

ExuluStorage

required

S3-backed storage accessor. Use utils.storage.read(s3key) to retrieve file content for file-backed contexts. For text-only items, this is not needed.

ChunkerResponse

Item & { id: string }

The original item, returned unchanged. Required.

string

The text content of this chunk. This is the text that will be embedded.

number

Zero-based position of this chunk. Must be contiguous (0, 1, 2, …) after filtering empty chunks — re-index with .map((c, i) => ({ ...c, index: i })) after any filtering step.

Record<string, unknown> | undefined

Arbitrary JSON-serializable metadata stored in the metadata JSONB column of the chunks table. Common uses: { page: 3 }, { section: "Introduction" }, { source_url: "https://..." }. Null bytes in string values are stripped automatically.

defaultChunker

import { defaultChunker } from "@exulu/backend";
import type { ChunkerOperation } from "@exulu/backend";

const defaultChunker: ChunkerOperation

The built-in ChunkerOperation used by ExuluContext when no chunker is configured. Concatenates item.name and item.content (falling back to item.description), runs SentenceChunker.create({ chunkSize: maxChunkSize }), and returns the results as a ChunkerResponse. Items with no usable text return { item, chunks: [] }.

Writing a custom chunker

Implement ChunkerOperation to handle file-backed, multi-source, or domain-specific chunking:

import type { ChunkerOperation } from "@exulu/backend";
import { ExuluChunkers } from "@exulu/backend";

export const myChunker: ChunkerOperation = async (item, maxChunkSize, utils) => {
  // For file-backed items:
  let text = "";
  if (item.document_s3key) {
    const buffer = await utils.storage.read(String(item.document_s3key));
    text = buffer.toString("utf-8");
  } else {
    text = [item.name, item.content].filter(Boolean).join("\n\n");
  }

  if (!text.trim()) return { item, chunks: [] };

  const chunker = await ExuluChunkers.sentence.create({
    chunkSize: maxChunkSize,
    chunkOverlap: Math.floor(maxChunkSize * 0.1),
  });
  const pieces = await chunker(text);

  return {
    item,
    chunks: pieces
      .map((c, index) => ({ content: c.text.trim(), index }))
      .filter((c) => c.content.length > 0)
      .map((c, index) => ({ ...c, index })),
  };
};

Assign it to the context:

import { ExuluContext } from "@exulu/backend";
import { myChunker } from "./my-chunker";

const docsContext = new ExuluContext({
  id: "docs",
  embedder: { model: "text-embedding-3-small" },
  chunker: myChunker,
  fields: [
    { name: "title", type: "text", required: true },
    { name: "document", type: "file", allowedFileTypes: [".pdf", ".txt"] },
    { name: "content", type: "longtext" },
  ],
  sources: [],
});

Start

Tutorials

Recipes

Core classes

Reference

Namespace import

SentenceChunker

SentenceChunker.create()

Calling the chunker

SentenceChunk properties

chunk()

Properties

RecursiveChunker

RecursiveChunker.create()

Calling the chunker

RecursiveChunk properties

chunk()

Properties

RecursiveRules

Constructor

Properties and methods

MarkdownChunker

chunk()

convertTablesToText()

ChunkerOperation and ChunkerResponse

ChunkerOperation parameters

ChunkerResponse

defaultChunker

Writing a custom chunker

Next steps

Configuration

ExuluContext

​Namespace import

​SentenceChunker

​SentenceChunker.create()

​Calling the chunker

​SentenceChunk properties

​chunk()

​Properties

​RecursiveChunker

​RecursiveChunker.create()

​Calling the chunker

​RecursiveChunk properties

​chunk()

​Properties

​RecursiveRules

​Constructor

​Properties and methods

​MarkdownChunker

​chunk()

​convertTablesToText()

​ChunkerOperation and ChunkerResponse

​ChunkerOperation parameters

​ChunkerResponse

​defaultChunker

​Writing a custom chunker

​Next steps

Configuration

ExuluContext

Namespace import

SentenceChunker

SentenceChunker.create()

Calling the chunker

SentenceChunk properties

chunk()

Properties

RecursiveChunker

RecursiveChunker.create()

Calling the chunker

RecursiveChunk properties

chunk()

Properties

RecursiveRules

Constructor

Properties and methods

MarkdownChunker

chunk()

convertTablesToText()

ChunkerOperation and ChunkerResponse

ChunkerOperation parameters

ChunkerResponse

defaultChunker

Writing a custom chunker

Next steps