---
title: "CogneeWriter"
id: cogneewriter
slug: "/cogneewriter"
description: "Writes ChatMessage objects to a CogneeMemoryStore as long-term memories."
---

# CogneeWriter

Writes `ChatMessage` objects to a `CogneeMemoryStore` as long-term memories.

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

|  |  |
| --- | --- |
| **Most common position in a pipeline** | After an [`Agent`](../agents-1/agent.mdx) or Chat Generator in memory-augmented pipelines |
| **Mandatory init variables** | `memory_store`: A `CogneeMemoryStore` instance |
| **Optional init variables** | `session_id`: When set, writes target the session-cache tier; when `None`, writes go to the permanent knowledge graph |
| **Mandatory run variables** | `messages`: A list of `ChatMessage` objects |
| **Optional run variables** | `user_id`: Cognee user ID to scope the write; pass `None` to use Cognee's default user |
| **Output variables** | `messages_written`: The list of `ChatMessage` objects that were written (passed through unchanged) |
| **API reference** | [Cognee](/reference/integrations-cognee#cogneewriter) |
| **GitHub link** | https://github.com/deepset-ai/haystack-core-integrations/tree/main/integrations/cognee |
| **Package name** | `cognee-haystack` |

</div>

## Overview

`CogneeWriter` persists a list of `ChatMessage` objects into a `CogneeMemoryStore`. Use it in a Haystack Pipeline to store conversation facts or user preferences after an Agent turn.

Messages are passed through unchanged to the pipeline output (`messages_written`), making this component easy to chain after an Agent or generator without breaking the pipeline flow.

The `session_id` init parameter controls which Cognee memory tier is targeted:

- Omit `session_id` (or set it to `None`) to write to the **permanent knowledge graph** — Cognee runs LLM extraction during ingestion, producing rich graph-completion-ready nodes.
- Set `session_id` to write to the **session cache** — fast writes with no LLM extraction, scoped to that session. Session content can later be promoted to the permanent graph via `CogneeMemoryStore.improve()`.

The writer's `session_id` overrides the store's `session_id` per call, so a single store can back multiple writers targeting different memory tiers.

## Installation

Install the Cognee integration:

```bash
pip install cognee-haystack
```

Set your LLM API key (used by Cognee for graph extraction):

```bash
export LLM_API_KEY="your-llm-api-key"
```

Optionally, set a separate embedding API key (defaults to `LLM_API_KEY` when unset):

```bash
export EMBEDDING_API_KEY="your-embedding-api-key"
```

## Usage

### On its own

```python
from haystack.dataclasses import ChatMessage

from haystack_integrations.components.writers.cognee import CogneeWriter
from haystack_integrations.memory_stores.cognee import CogneeMemoryStore

store = CogneeMemoryStore()
writer = CogneeWriter(memory_store=store)

result = writer.run(
    messages=[ChatMessage.from_user("Alice prefers concise Python examples.")],
    user_id="a1b2c3d4-e5f6-7890-abcd-ef1234567890",
)
print(result["messages_written"])
```

To write to the session cache instead of the permanent graph, pass a `session_id`:

```python
session_writer = CogneeWriter(memory_store=store, session_id="alice_session_1")
session_writer.run(
    messages=[ChatMessage.from_user("Alice is currently debugging a vector store issue.")],
    user_id="a1b2c3d4-e5f6-7890-abcd-ef1234567890",
)
```

### In a Pipeline

This example connects an Agent's full `messages` output to `CogneeWriter`, so Cognee stores the conversation turn in the permanent graph.

```python
from haystack import Pipeline
from haystack.components.agents import Agent
from haystack.components.generators.chat import OpenAIChatGenerator
from haystack.dataclasses import ChatMessage

from haystack_integrations.components.writers.cognee import CogneeWriter
from haystack_integrations.memory_stores.cognee import CogneeMemoryStore

store = CogneeMemoryStore(dataset_name="my_agent_memory")

pipeline = Pipeline()
pipeline.add_component(
    "agent",
    Agent(
        chat_generator=OpenAIChatGenerator(model="gpt-4o-mini"),
        system_prompt=(
            "Answer the user and preserve durable user facts or preferences for future conversations."
        ),
    ),
)
pipeline.add_component("writer", CogneeWriter(memory_store=store))

pipeline.connect("agent.messages", "writer.messages")

result = pipeline.run(
    {
        "agent": {
            "messages": [
                ChatMessage.from_user(
                    "My name is Alice and I prefer concise Python examples.",
                ),
            ],
        },
        "writer": {
            "user_id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
        },
    },
)

print(result["writer"]["messages_written"])
```
