---
title: Persistent memory for LangChain in Elixir, on your own machine
slug: semurg-memory-for-langchain-elixir
date: 2026-10-25
author: Semurg
section: how-to
tags: [langchain, elixir, mcp, agents, memory, how-to]
summary: Give an Elixir LangChain agent a memory that outlives the session, on your own disk, through the langchain_mcp adapter over streamable HTTP, with the exact program our tests run.
status: published
covers: [route:POST /v1/mcp, route:POST /v1/memory/recall, mcp:memory_remember, mcp:memory_recall]
constants: [24.04, 1.18]
---
> Last checked on r11.132.20261027.a274a28 (27 Oct 2026): every command below ran on a fresh node of that release. The current release is r11.135.20261028.2ff2348 (28 Oct 2026), and the commands have not been re-checked on it yet.

> Tested end to end with `langchain 0.4.1`, `langchain_mcp 0.2.0`, `anubis_mcp 0.16.0` and `plug 1.20.3`. The release it ran on is named in the checked line at the top of this page.

An agent built with LangChain for Elixir forgets what it learned when its process ends. This guide gives it a memory that outlives the
process: a Semurg node on your own machine, reached through the `langchain_mcp` adapter, where every fact stays on your disk and comes
back cited to where it was said. Any other agent or framework that uses the same node and the same scope reads the same memory.

> Diagram langchain-elixir-memory: Your Elixir program stores a fact through LangChain's MCP adapter; your node keeps it in the scope you named, on your own disk; a later run, another agent or a plain HTTP call on the same scope reads it back, cited.

## What you need

- An Intel or AMD x86_64 machine with Ubuntu 24.04, on Linux directly or on Windows through WSL2. One node is free, with no licence key.
- Elixir 1.18 with Erlang/OTP, installed the way you prefer. We test in the official `elixir:1.18-slim` container.

## Step one: install a node

On Ubuntu 24.04 (x86_64), with sudo:

```bash
curl -fsSL https://one.semurg.io/install | sudo bash
```

The [install page](/install) lists what the installer needs and what it changes. The installer ends by printing your API token, and the
node keeps a copy. Put it in a file only you can read, and have every new terminal load it:

```bash
mkdir -p ~/.config/semurg
(umask 077; sudo grep '^SEMURG_API_TOKEN=' /etc/semurg/semurg.env | cut -d= -f2- > ~/.config/semurg/token)
echo 'export SEMURG_API_TOKEN="$(cat ~/.config/semurg/token)"' >> ~/.bashrc
export SEMURG_API_TOKEN="$(cat ~/.config/semurg/token)"
```

## Step two: the packages

There is nothing to install by hand. The program's first line fetches and compiles LangChain, its MCP adapter and Plug on the first run
(the adapter compiles a small test server that needs Plug):

```elixir
Mix.install([{:langchain, "~> 0.4"}, {:langchain_mcp, "~> 0.2"}, {:plug, "~> 1.0"}])
```

On a fresh Elixir install, fetch the package tools once first, as our test setup does:

```bash
mix local.hex --force
mix local.rebar --force
```

## Step three: connect

Save the program below as `snippet.exs`. It is the program our tests run as written, shown here from the
[agents page](/agents#elixir-langchain) rather than copied, so what you read is always the file that ran.

```elixir
# Run: elixir snippet.exs   (SEMURG_API_TOKEN must be set in the environment)
Mix.install([{:langchain, "~> 0.4"}, {:langchain_mcp, "~> 0.2"}, {:plug, "~> 1.0"}])   # langchain_mcp compiles a test server that needs Plug.Router

Logger.configure(level: :warning)   # the MCP client logs every request at debug level

url = URI.parse(System.get_env("SEMURG_MCP_URL", "http://127.0.0.1:4000/v1/mcp"))
headers = %{
  "Authorization" => "Bearer " <> System.fetch_env!("SEMURG_API_TOKEN"),
  "X-Semurg-Scope" => System.get_env("SEMURG_MCP_SCOPE", "default")
}
facts = %{
  "entities" => [%{"name" => "Ada", "type" => "person"}, %{"name" => "Acme", "type" => "organisation"}],
  "relations" => [%{"source" => "Ada", "target" => "Acme", "type" => "WORKS_AT"}]
}

defmodule Semurg.MCP do
  use LangChain.MCP.Client, name: "semurg", version: "1.0.0", protocol_version: "2025-03-26"
end

{:ok, _} = Semurg.MCP.start_link(transport: {:streamable_http, base_url: "#{url.scheme}://#{url.host}:#{url.port}", mcp_path: url.path, headers: headers})
adapter = LangChain.MCP.Adapter.new(client: Semurg.MCP)

# the client does its MCP handshake in the background: ask until the memory tools are listed
wait = fn wait, tries ->
  tools = LangChain.MCP.Adapter.to_functions(adapter)
  cond do
    length(tools) >= 6 -> tools
    tries == 0 -> raise "the node listed no memory tools"
    true -> Process.sleep(500); wait.(wait, tries - 1)
  end
end

by_name = wait.(wait, 60) |> Map.new(&{&1.name, &1})
by_name["memory_remember"].function.(%{"facts" => facts}, %{})
IO.inspect(by_name["memory_recall"].function.(%{"subject" => "Ada"}, %{}), limit: :infinity, printable_limit: :infinity)
System.halt(0)
```

*Ran: this exact file, end to end against a fresh node on release r11.132.20261027.a274a28, with langchain 0.4.1, langchain_mcp 0.2.0, anubis_mcp 0.16.0, plug 1.20.3. Install: `Mix.install([{:langchain, "~> 0.4"}, {:langchain_mcp, "~> 0.2"}, {:plug, "~> 1.0"}])`. Its run record: https://one.semurg.io/agents#elixir-langchain*

It reads your token from `SEMURG_API_TOKEN`, the node's address from `SEMURG_MCP_URL` (without it, `http://127.0.0.1:4000/v1/mcp`) and
the scope from `SEMURG_MCP_SCOPE` (without it, the scope named `default`). It defines a client module with `use LangChain.MCP.Client`,
starts it over the streamable HTTP transport with the token and the `X-Semurg-Scope` header, waits until the node's tools are listed,
stores two facts with `memory_remember` (Ada works at Acme) and prints what `memory_recall` returns for Ada.

## Step four: run it

Give the program a scope of its own, so it never writes into a memory you use for real work:

```bash
export SEMURG_MCP_SCOPE=try-elixir-langchain
elixir snippet.exs
```

The first run is slower, because it fetches and compiles the packages. The program then inspects the recall result, which carries the
node's answer for Ada: `state` set to `answered` and the `WORKS_AT` fact that links Ada to Acme, each item cited. Storing the same facts
again changes nothing, so it is safe to run twice.

Now read the same fact from outside Elixir, over plain HTTP. What one client writes, any other client on the same node and scope reads:

```bash
curl -sS http://127.0.0.1:4000/v1/memory/recall \
  -H "Authorization: Bearer $SEMURG_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"scope":"try-elixir-langchain","subject":"Ada"}'
```

## The memory tools in LangChain for Elixir

`LangChain.MCP.Adapter.to_functions` returns each memory tool as a LangChain function with the same name; the program calls its
`function` directly. The same functions are what you add to a LangChain chain, and the model then chooses (our test calls them directly,
without a model).

- `memory_status`: reports whether shared memory is on for this node and which of your scopes hold facts.
- `memory_remember`: stores entities, the relationships between them and the passages they came from, or plain text, with an optional source label and date.
- `memory_recall`: recalls what is stored about one named entity, its own facts first, each item cited.
- `memory_relate`: adds one typed relationship between two entities in a scope, creating an end that is not stored yet.
- `memory_context`: answers a question in plain words with cited items and a verdict on whether the store covers it.
- `memory_document`: takes a whole document (PDF with a text layer, Word, HTML or plain text) and stores it as cited passages in a scope.
- `memory_forget`: deletes one thing per call: an entity and everything that names it, one fact, one document, every document under a source label, or the whole scope. It is unreachable at once and not yet wiped from the disk.
- `memory_export`: reads everything a scope holds, one page per call: send each reply's `next` back as `cursor` until it is empty. The records are the entities, the facts with their dated sources and whether each is current or ended, and each stored document once; a forgotten passage is never exported.
- `memory_import`: stores the records `memory_export` produced into any scope, through the same writes `memory_remember` makes. A page sent twice stores nothing twice, and the reply names every record it skipped.

Every answer says its `state`: `answered`, `nothing_stored` (nothing stored matched, so the agent should say it does not know) or `could_not_judge`.

## Troubleshooting

- An error that the environment variable `SEMURG_API_TOKEN` is not set: run the last line of step one, or open a new terminal.
- `Mix.install` cannot fetch the packages on a fresh Elixir: run the two `mix local` lines of step two once.
- `the node listed no memory tools`: the client never finished its handshake while the program waited. Check the token and the address first.
- The program sets the log level to warning because the MCP client logs every request at debug level; remove that line to watch each request.
- After the node restarts (an update restarts it), the first call can fail; in our October 2026 restart test, run on an earlier release, the client then reconnected by itself. For a node that is up but stalled, set the per-call timeout your framework offers.

Use `127.0.0.1` rather than `localhost`: on Ubuntu `localhost` can resolve to the IPv6 address first, and the node listens on IPv4 loopback
only. To reach a node on another machine, set `SEMURG_MCP_URL`, or forward its port with `ssh -N -L 4000:127.0.0.1:4000 you@your-node`.

## Next

- The [agents page](/agents): every framework program, with its versions and the release it last ran on in our tests.
- [Give your agent persistent memory with MCP in five minutes](/blog/agent-memory-mcp-five-minutes): the memory calls over plain HTTP too.
- [Connecting to Semurg over MCP](/blog/connect-over-mcp): the endpoint, the protocol versions it speaks and how a refusal comes back.
- If a step does not work, tell us on the [contact page](/contact), with the reply you got.

*This post was written with AI assistance. Every result in it is checked against a published release or record before the post goes out.*