Ephemeral Buffer MCP Server (ephemeral-buffer)

Ephemeral Buffer is an MCP server and command-line client for capturing command output in a bounded, searchable buffer. Coding agents can search captures and retrieve relevant portions instead of carrying entire build and test logs in their conversation context.

Quick start

Requires Python 3.10 or newer. Install the package in an isolated environment.

macOS and Linux

python3 -m venv .venv
.venv/bin/python -m pip install --upgrade pip
.venv/bin/python -m pip install ephemeral-buffer-mcp

Configure your MCP client using the user guide. For an isolated server, the server and ephbuf must use the same unique session ID. On macOS/Linux, export the ID before starting Codex with the launcher installed in the virtual environment:

export EPHEMERAL_SESSION_ID=quick-start-session
.venv/bin/codex-ephemeral

Set the same value in another MCP client's server environment. Then capture command output with ephbuf, passing the same ID.

macOS and Linux

.venv/bin/python -c 'print("Hello from a captured command")' 2>&1 |
  EPHEMERAL_SESSION_ID=quick-start-session .venv/bin/ephbuf --label "quick start"

Windows installation steps are in the user guide's Windows support section. Windows runtime behavior isn't covered by CI; that section describes the unverified CLI capture and process-control paths.

The agent can then search the capture and retrieve bounded slices through the MCP tools.

Context reduction in one agent comparison

In a five-repetition gpt-6-luna comparison run on 2026-10-09, mean MCP tool-response bytes fell from 6,681 to 1,501 (77.5%); the Codex context proxy fell from 23,910 to 17,643 bytes (26.2%). This is a result from one workload, not a general savings guarantee. The context figure is a prompt/event-envelope proxy, not the model's internal context size. See the benchmark methodology and comparison details.

Documentation