mcp-envoy-wasm

Local LibreChat + MCP + http-streamable + Envoy Setup

TODO add intro

Prerequisites

• Docker/podman
• node.js/npm/npx - https://nodejs.org/en/download
• rust - https://www.rust-lang.org/tools/install

Streamable HTTP MCP Server (Everything)

Important: Run this before librechat as it attempts to conenct to any configured mcp servers at startup

Setup and running locally

Install & run an MCP Server with Streamable HTTP support. For more info see mcp-server

npx @modelcontextprotocol/server-everything streamableHttp

Test it out

curl http://localhost:3001/mcp

The response should look something like this:

{"jsonrpc":"2.0","error":{"code":-32000,"message":"Bad Request: No valid session ID provided"}}

Wasm module & Envoy Proxy

Important: Run this before librechat as it attempts to conenct to any configured mcp servers at startup

Setup

Build the wasm module. This command outputs the wasm binary to the ./target folder.

cargo build --target wasm32-wasip1 --release

Start envoy with the wasm binary and envoy config mounted as path volumes. The envoy config will route traffic from /mcp to the mcp server started on port 3001, proxying through the wasm module.

docker run --rm -it   -v "$PWD/target/wasm32-wasip1/release/mcp_wasm_filter.wasm:/etc/envoy/mcp_wasm_filter.wasm"   -v "$PWD/envoy/envoy.yaml:/etc/envoy/envoy.yaml"   -p 10000:10000 -p 9901:9901   envoyproxy/envoy-dev:latest

Test it out

Initialise an mcp connection to the server

curl -v http://localhost:10000/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{
    "jsonrpc": "2.0",
    "id": "1",
    "method": "initialize",
    "params": {"protocolVersion":"2024-11-05","capabilities":{"sampling":{},"roots":{"listChanged":true}},"clientInfo":{"name":"my-client","version":"0.7.2"}}
  }'

The response should look something like this:

event: message
id: 38134b7b-a51a-4edb-b169-cc741f23df88_1750105674999_8lup021w
data: {"result":{"protocolVersion":"2024-11-05","capabilities":{"prompts":{},"resources":{"subscribe":true},"tools":{},"logging":{},"completions":{}},"serverInfo":{"name":"example-servers/everything","version":"1.0.0"}},"jsonrpc":"2.0","id":"1"}

There should also be some logs in the envoy output like this:

[2025-06-16 16:36:59.563][38][info][wasm] [source/extensions/common/wasm/context.cc:1137] wasm log mcp_wasm_filter_root my_vm: vm start called

...

[2025-06-16 20:42:19.595][41][info][wasm] [source/extensions/common/wasm/context.cc:1137] wasm log mcp_wasm_filter mcp_wasm_filter_root my_vm: on_http_request_body called
[2025-06-16 20:42:19.595][41][info][wasm] [source/extensions/common/wasm/context.cc:1137] wasm log mcp_wasm_filter mcp_wasm_filter_root my_vm: Appending 229 bytes to buffer
[2025-06-16 20:42:19.595][41][info][wasm] [source/extensions/common/wasm/context.cc:1137] wasm log mcp_wasm_filter mcp_wasm_filter_root my_vm: on_http_request_body called
[2025-06-16 20:42:19.595][41][info][wasm] [source/extensions/common/wasm/context.cc:1137] wasm log mcp_wasm_filter mcp_wasm_filter_root my_vm: Wasm filter: Got request body! body_size: 0

LibreChat

Bring it all together in the Librechat UI

Run LibreChat Locally

Once off config setup:

cp librechat/.env.template librechat/.env

Start the services:

cd librechat
docker compose up -d

LibreChat should now be running at http://localhost:3080 The mcp server should show up in the UI, and allow you to exec the tool using a prompt like add 7 and 3. You'll need to select an AI provider and model from the dropdown at the top first, and set an API Key (unless you have a custom model/endpoint set up in librechat you can use). For example, you can use a Gemini API Key on the free tier to test this out.

MCP Inspector

For a more direct & possibly quicker way to generate mcp traffic, you can use the mcp-inspector tool. Start it with this:

DANGEROUSLY_OMIT_AUTH=true npx @modelcontextprotocol/inspector

then open http://localhost:6274/?transport=streamable-http&serverUrl=http://localhost:10000/mcp and click 'Connect'. This should connect the browser directly to the mcp server via envoy proxy. Then use tools from the Tools tab (printEnv is good for testing as there's no params). Just click 'Run Tool' repeatedly in the UI to generate mcp traffic.