diff --git a/CHANGELOG.md b/CHANGELOG.md
index a3bdaef..bbacb39 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,9 @@ Notable changes to Swarmail. Versions follow [semantic versioning](https://semve
   which is the default. A page of 20 messages took 48 µs instead of 57 µs with 2 KB bodies and 52 µs instead of 82 µs
   with 17 KB bodies.
 
+- The `swarmail-mcp` README lists the memory each launch command costs: about 180 MiB for `npx -y swarmail-mcp`, 82 MiB
+  for `bunx swarmail-mcp` and 46 MiB for `bunx --bun swarmail-mcp`, which runs the same relay under Bun.
+
 ## 0.5.2 - 2026-10-09
 
 - Require agents to record whole-session closeouts and retire their own project
diff --git a/packages/mcp-relay/README.md b/packages/mcp-relay/README.md
index 8e3c851..169032e 100644
--- a/packages/mcp-relay/README.md
+++ b/packages/mcp-relay/README.md
@@ -17,3 +17,21 @@ It forwards each JSON-RPC message to `SWARMAIL_URL`
 (default `http://127.0.0.1:18765/mcp/`). Node 18 or newer, no dependencies.
 Hosts that support MCP over HTTP can skip the relay and use that URL directly,
 which is what `scripts/configure-mcp.ts` sets up.
+
+## Memory
+
+Each MCP client that launches the relay keeps its own process tree running.
+On one Linux machine, with the relay idle after a first request:
+
+| Command                   | Memory, whole process tree |
+| ------------------------- | -------------------------- |
+| `npx -y swarmail-mcp`     | about 180 MiB              |
+| `bunx swarmail-mcp`       | about 82 MiB               |
+| `bunx --bun swarmail-mcp` | about 46 MiB               |
+
+Most of the `npx` figure is the `npm exec` process that stays running beside
+the relay. `bunx` alone still runs the relay under Node, because the script's
+`#!/usr/bin/env node` line wins; `--bun` runs it under Bun. The relay is plain
+JavaScript with no dependencies, so it runs unchanged under Bun, but the
+repository's relay tests run it under Node only. Use `--bun` only where Bun is
+installed.