---
title: "VLLMDocumentEmbedder"
id: vllmdocumentembedder
slug: "/vllmdocumentembedder"
description: "This component computes the embeddings of a list of documents using models served with vLLM."
---

# VLLMDocumentEmbedder

This component computes the embeddings of a list of documents using models served with [vLLM](https://docs.vllm.ai/).

<div className="key-value-table">

|  |  |
| --- | --- |
| **Most common position in a pipeline** | Before a [`DocumentWriter`](../writers/documentwriter.mdx) in an indexing pipeline         |
| **Mandatory init variables**           | `model`: The name of the model served by vLLM                                              |
| **Mandatory run variables**            | `documents`: A list of documents                                                           |
| **Output variables**                   | `documents`: A list of documents (enriched with embeddings)                                |
| **API reference**                      | [vLLM](/reference/integrations-vllm)                                                       |
| **GitHub link**                        | https://github.com/deepset-ai/haystack-core-integrations/tree/main/integrations/vllm      |
| **Package name** | `vllm-haystack` |

</div>

## Overview

[vLLM](https://docs.vllm.ai/) is a high-throughput and memory-efficient inference and serving engine for LLMs. It exposes an OpenAI-compatible HTTP server, which `VLLMDocumentEmbedder` uses to compute embeddings through the Embeddings API.

`VLLMDocumentEmbedder` computes the embeddings of a list of documents and stores the obtained vectors in the `embedding` field of each document. It expects a vLLM server to be running and accessible at the `api_base_url` parameter (by default, `http://localhost:8000/v1`). To embed a string (such as a query), use the [`VLLMTextEmbedder`](vllmtextembedder.mdx).

The vectors computed by this component are necessary to perform embedding retrieval on a collection of documents. At retrieval time, the vector that represents the query is compared with those of the documents to find the most similar or relevant ones.

If the vLLM server was started with `--api-key`, provide the API key through the `VLLM_API_KEY` environment variable or the `api_key` init parameter using Haystack's [Secret](../../concepts/secret-management.mdx) API.

### Compatible models

vLLM supports a range of embedding models. Check the [vLLM pooling models docs](https://docs.vllm.ai/en/stable/models/pooling_models) for the list of supported architectures and models.

### vLLM-specific parameters

You can pass vLLM-specific parameters through the `extra_parameters` dictionary. These are forwarded as `extra_body` to the OpenAI-compatible embeddings endpoint. Use this to pass parameters that are not part of the standard OpenAI Embeddings API, such as `truncate_prompt_tokens` or `truncation_side`. See the [vLLM Embeddings API docs](https://docs.vllm.ai/en/stable/models/pooling_models/embed/#openai-compatible-embeddings-api) for details.

```python
embedder = VLLMDocumentEmbedder(
    model="google/embeddinggemma-300m",
    extra_parameters={"truncate_prompt_tokens": 256, "truncation_side": "right"},
)
```

### Matryoshka embeddings

If the model was trained with Matryoshka Representation Learning, you can reduce the dimensionality of the output vector through the `dimensions` parameter. See the [vLLM Matryoshka docs](https://docs.vllm.ai/en/stable/models/pooling_models/embed/#matryoshka-embeddings) for details.

### Batching and failure handling

`VLLMDocumentEmbedder` encodes documents in batches. Use `batch_size` (default `32`) to control how many documents are sent in a single request to the vLLM server, and `progress_bar` to toggle the progress indicator.

By default (`raise_on_failure=False`), failed embedding requests are logged and processing continues with the remaining documents. Set `raise_on_failure=True` to raise an exception instead.

### Instructions

Some embedding models require prepending the document text with an instruction to work better for retrieval. For example, if you use [intfloat/e5-large-v2](https://huggingface.co/intfloat/e5-large-v2), you should prefix your document with the following instruction: "passage:".

This is how it works with `VLLMDocumentEmbedder`:

```python
instruction = "passage:"
embedder = VLLMDocumentEmbedder(
    model="intfloat/e5-large-v2",
    prefix=instruction,
)
```

### Embedding metadata

Documents often come with a set of metadata. If they are distinctive and semantically meaningful, you can embed them along with the text of the document to improve retrieval. Pass the relevant fields through `meta_fields_to_embed`; they are concatenated to the document text using `embedding_separator` (a newline by default):

```python
from haystack import Document
from haystack_integrations.components.embedders.vllm import VLLMDocumentEmbedder

doc = Document(content="some text", meta={"title": "relevant title", "page_number": 18})

embedder = VLLMDocumentEmbedder(
    model="google/embeddinggemma-300m",
    meta_fields_to_embed=["title"],
)

docs_with_embeddings = embedder.run(documents=[doc])["documents"]
```

## Usage

Install the `vllm-haystack` package to use the `VLLMDocumentEmbedder`:

```shell
pip install vllm-haystack
```

### Starting the vLLM server

Before using this component, start a vLLM server with an embedding model:

```bash
vllm serve google/embeddinggemma-300m
```

For details on server options, see the [vLLM CLI docs](https://docs.vllm.ai/en/stable/cli/serve/).

### On its own

```python
from haystack import Document
from haystack_integrations.components.embedders.vllm import VLLMDocumentEmbedder

doc = Document(content="I love pizza!")

document_embedder = VLLMDocumentEmbedder(model="google/embeddinggemma-300m")

result = document_embedder.run([doc])
print(result["documents"][0].embedding)

# [-0.0215301513671875, 0.01499176025390625, ...]
```

### In a pipeline

```python
from haystack import Document, Pipeline
from haystack.components.retrievers.in_memory import InMemoryEmbeddingRetriever
from haystack.components.writers import DocumentWriter
from haystack.document_stores.in_memory import InMemoryDocumentStore
from haystack.document_stores.types import DuplicatePolicy
from haystack_integrations.components.embedders.vllm import (
    VLLMDocumentEmbedder,
    VLLMTextEmbedder,
)

document_store = InMemoryDocumentStore(embedding_similarity_function="cosine")

documents = [
    Document(content="My name is Wolfgang and I live in Berlin"),
    Document(content="I saw a black horse running"),
    Document(content="Germany has many big cities"),
]

document_embedder = VLLMDocumentEmbedder(model="google/embeddinggemma-300m")
writer = DocumentWriter(document_store=document_store, policy=DuplicatePolicy.OVERWRITE)

indexing_pipeline = Pipeline()
indexing_pipeline.add_component("document_embedder", document_embedder)
indexing_pipeline.add_component("writer", writer)
indexing_pipeline.connect("document_embedder", "writer")

indexing_pipeline.run({"document_embedder": {"documents": documents}})

query_pipeline = Pipeline()
query_pipeline.add_component(
    "text_embedder",
    VLLMTextEmbedder(model="google/embeddinggemma-300m"),
)
query_pipeline.add_component(
    "retriever",
    InMemoryEmbeddingRetriever(document_store=document_store),
)
query_pipeline.connect("text_embedder.embedding", "retriever.query_embedding")

query = "Who lives in Berlin?"

result = query_pipeline.run({"text_embedder": {"text": query}})

print(result["retriever"]["documents"][0])

# Document(id=..., content: 'My name is Wolfgang and I live in Berlin', score: ...)
```
