Use the LLM parser

This page explains how to use the Vertex AI RAG Engine LLM parser.

Introduction

Vertex AI RAG Engine uses LLMs for document parsing. LLMs have the ability to effectively process documents in the following ways:

  • Understand and interpret semantic content across various formats.
  • Retrieve relevant document chunks.
  • Extract meaningful information from documents.
  • Identify relevant sections in documents.
  • Accurately summarize complex documents.
  • Understand and interact with visuals.
  • Extract data from charts and diagrams.
  • Describe images.
  • Understand relationships between charts and text.
  • Provide more contextually rich and accurate responses.

The capabilities of the Vertex AI RAG Engine significantly improves the quality of generated responses.

Supported models

The LLM parser only supports Gemini models. If you have the RAG API enabled, you have access to the supported models. For a list of supported generation models, see Generative models.

Supported file types

The following file types are supported by the LLM parser:

  • application/pdf
  • image/png
  • image/jpeg
  • image/webp
  • image/heic
  • image/heif

Pricing and quotas

For pricing details, see Vertex AI pricing.

For quotas that apply, see Rate quotas.

The LLM parser calls Gemini models to parse your documents. This creates additional costs, which are charged to your project. The cost can be roughly estimated using this formula:

cost = number_of_document_files * average_pages_per_document *
(average_input_tokens * input_token_pricing_of_selected_model +
average_output_tokens * output_token_pricing_of_selected_model)

For example, you have 1,000 PDF files, and each PDF file has 50 pages. The average PDF page has 500 tokens, and we need an additional 100 tokens for prompting. The average output is 100 tokens.

Gemini 2.0 Flash-Lite is used in your configuration for parsing, and it costs $0.075 for 1M input tokens and $0.3 for output text tokens.

cost = 1,000 * 50 * (600 * 0.075 / 1M + 100 * 0.3 / 1M) = 3.75

The cost is $3.75.

Import files with LlmParser enabled

Replace the values in the following variables used in the code samples:

  • PROJECT_ID: The ID for your Google Cloud project.
  • LOCATION: The region where your request is processed.
  • RAG_CORPUS_RESOURCE: The ID of your corpus.
  • GCS_URI: The Cloud Storage URI of the files you want to import.
  • GOOGLE_DRIVE_URI: The Google Drive URI of the files you want to import.
  • MODEL_NAME: The resource name of the model used for parsing.

    Format: projects/{project_id}/locations/{location}/publishers/google/models/{model_id}

  • CUSTOM_PARSING_PROMPT: Optional: Custom prompt that is configured by the customer for LLM parser to use for parsing documents.

  • MAX_PARSING_REQUESTS_PER_MIN: Optional: The maximum number of requests the job can make to the Vertex AI model per minute. For more information, see Generative AI on Vertex AI rate limits and the Quotas & System Limits page for your project to set an appropriate value.

REST 

  curl -X POST \
    -H "Content-Type: application/json" \
    -H "Authorization: Bearer $(gcloud auth print-access-token)" \
  "https://LOCATION-aiplatform.googleapis.com/v1beta1/projects/PROJECT_ID/locations/LOCATION/ragCorpora/RAG_CORPUS_RESOURCE/ragFiles:import" -d '{
    "import_rag_files_config": {
      "gcs_source": {
        "uris":  ["GCS_URI", "GOOGLE_DRIVE_URI"]
      },
      "rag_file_chunking_config": {
        "chunk_size": 512,
        "chunk_overlap": 102
      },
      "rag_file_parsing_config": {
        "llm_parser": {
          "model_name": "MODEL_NAME",
          "custom_parsing_prompt": "CUSTOM_PARSING_PROMPT"
          "max_parsing_requests_per_min": "MAX_PARSING_REQUESTS_PER_MIN"
        }
      }
    }
  }'

Python

To learn how to install or update the Vertex AI SDK for Python, see Install the Vertex AI SDK for Python. For more information, see the Python API reference documentation.

  from vertexai import rag
  import vertexai

  PROJECT_ID = "PROJECT_ID"
  CORPUS_NAME = "RAG_CORPUS_RESOURCE"
  LOCATION = "LOCATION"
  MODEL_ID = "MODEL_ID"
  MODEL_NAME = "projects/{PROJECT_ID}/locations/{LOCATION}/publishers/google/models/{MODEL_ID}"
  MAX_PARSING_REQUESTS_PER_MIN = MAX_PARSING_REQUESTS_PER_MIN # Optional
  CUSTOM_PARSING_PROMPT = "Your custom prompt" # Optional

  PATHS = ["https://drive.google.com/file/123", "gs://my_bucket/my_files_dir"]

  # Initialize Vertex AI API once per session
  vertexai.init(project={PROJECT_ID}, location={LOCATION})

  transformation_config = rag.TransformationConfig(
      chunking_config=rag.ChunkingConfig(
          chunk_size=1024, # Optional
          chunk_overlap=200, # Optional
      ),
  )

  llm_parser_config = rag.LlmParserConfig(
      model_name = MODEL_NAME,
      max_parsing_requests_per_min=MAX_PARSING_REQUESTS_PER_MIN, # Optional
      custom_parsing_prompt=CUSTOM_PARSING_PROMPT, # Optional
  )

  rag.import_files(
      CORPUS_NAME,
      PATHS,
      llm_parser=llm_parser_config,
      transformation_config=transformation_config,
  )

Prompting

The Vertex AI RAG Engine LLM parser uses a predefined and tuned prompt for parsing documents. However, if you have specialized documents that might not be suitable for a general prompt, you have the option to specify your custom parsing prompt when using the API. When requesting Gemini to parse your documents, Vertex AI RAG Engine appends a prompt to your default system prompt.

Prompt template table

To help with document parsing, the following table provides a prompt template example to guide you in creating prompts that Vertex AI RAG Engine can use to parse your documents:

Instruction Template statement Example
Specify role. You are a/an [Specify the role, such as a factual data extractor or an information retriever]. You are an information retriever.
Specify task. Extract [Specify the type of information, such as factual statements, key data, or specific details] from the [Specify the document source, such as a document, text, article, image, table]. Extract key data from the sample.txt file.
Explain how you want the LLM to generate the output according to your documents. Present each fact in a [Specify the output format, such as a structured list or text format], and link to its [Specify the source location, such as a page, paragraph, table, or row]. Present each fact in a structured list, and link to its sample page.
Highlight what should be the focus of the LLM. Extract [Specify the key data types, such as the names, dates, numbers, attributes, or relationships] exactly as stated. Extract names and dates.
Highlight what you want the LLM to avoid. [List the actions to avoid, such as analysis, interpretation, summarizing, inferring, or giving opinions]. Extract only what the document explicitly says. No giving opinions. Extract only what the document explicitly says.

General guidance

Follow these guidelines to write your prompt to send to the LLM parser.

  • Specific: Clearly define the task and the type of information to be extracted.
  • Detailed: Provide detailed instructions on output format, source attribution, and handling of different data structures.
  • Constraining: Explicitly state what the AI shouldn't do such as analysis or interpretation.
  • Clear: Use clear and directive language.
  • Structured: Organize instructions logically using numbered lists or bullet points for readability.

Parsing quality analysis

This table lists results from scenarios that customers ran using Vertex AI RAG Engine. The feedback shows that the LLM parser improves the quality of parsing documents.

Scenario Result
Parsing information across slides and linking sections The LLM parser successfully linked section titles on one slide to the detailed information presented on subsequent slides.
Understanding and extracting information from tables The LLM parser correctly related columns and headers within a large table to answer specific questions.
Interpreting flowcharts The LLM parser was able to follow the logic of a flowchart and extract the correct sequence of actions and corresponding information.
Extracting data from graphs The LLM parser could interpret different types of graphs, such as line graphs, and extract specific data points based on the query.
Capturing relationships between headings and text The LLM parser, guided by the prompt, paid attention to heading structures and could retrieve all relevant information associated with a particular topic or section.
Potential to overcome embedding limitations with prompt engineering While initially hampered by embedding model limitations in some use cases, additional experiments demonstrated that a well-crafted LLM parser prompt could potentially mitigate these issues and retrieve the correct information even when semantic understanding is challenging for the embedding model alone.

The LLM parser enhances the LLM's ability to understand and reason about the context within a document, which leads to more accurate and comprehensive responses.

Retrieval query

After you enter a prompt that's sent to a generative AI model, the retrieval component in RAG searches through its knowledge base to find information that's relevant to the query. For an example of retrieving RAG files from a corpus based on a query text, see Retrieval query.

What's next