ProxyCAUTION
A TypeScript streamable HTTP and SSE proxy for MCP servers that use stdio transport.
Overview
From the repository's own README, as read at the audited commit. Badges and raw HTML are left out.
A TypeScript streamable HTTP and SSE proxy for MCP servers that use stdio transport.
[!NOTE] CORS is enabled by default with configurable options. See CORS Configuration for details.
[!NOTE] For the inverse — giving a stdio-only client access to a remote MCP server, including the interactive OAuth flow — see mcp-remote.
[!NOTE] MCP Proxy is what FastMCP uses to enable streamable HTTP and SSE.
Protocol revisions
MCP Proxy serves protocol revision 2026-07-28 and the 2025-era revisions (2024-10-07 through 2025-11-25) from the same endpoint. Every POST to the streamable HTTP endpoint is classified by its own content — the 2026-07-28 revision puts a _meta envelope on every request, and requests without one are served by the 2025-era session machinery — so old and new clients share one URL and neither has to know the other exists.
Progress notifications and cancellation cross the proxy in both eras: a forwarded call carries the caller's abort signal, and relayed progress is re-tagged with the token the caller sent.
Use --no-modern to serve only 2025-era clients; a 2026-07-28 client is then answered by the 2025-era machinery, which does not recognise its request. The modern leg lives on the streamable HTTP endpoint, so it is also absent when that endpoint is disabled (--server sse, or streamEndpoint: null).
The upstream connection
402713e9bf0eOBSERVED · 2026-10-05Connect
Built from this server's own package name, version and transport as found in its source — not copied from anyone's documentation, so it cannot drift against a page we do not control.
claude mcp add mcp-proxy -- npx -y [email protected]
{
"mcpServers": {
"mcp-proxy": {
"command": "npx",
"args": [
"-y",
"[email protected]"
]
}
}
}Exposed tools (1)
1 read · 0 write · 0 destructive.
| Tool | Risk | Description |
|---|---|---|
ping | read |
Trust audit
CAUTIONgrade B · trust 80/100 Install with care. The audit found things worth knowing before you trust its output.
| Layer | What it checks | Result |
|---|---|---|
| L0 | Provenance & inventory | PASS |
| L1 | Static analysis of the code | WARN |
| L2 | Instruction surface (what it tells the agent) | PASS |
| L3 | Class-specific surface | PASS |
| L4 | Behavioural (sandbox) | SKIPPED |
What the source does
- Filesystem
- declared (1 observation(s))
- Network
- none-observed
- Shell
- none-observed
- Dependencies
- not all pinned
- Secrets in source
- found
Findings (13)
const apiKey = "test-api-key-unhandled";
-----BEGIN PRIVATE KEY-----
-----BEGIN PRIVATE KEY-----
-----BEGIN PRIVATE KEY-----
const packageJson = require("../../package.json") as { version: string };url: "http://127.0.0.1:8080/sse",
new StreamableHTTPClientTransport(new URL(`http://127.0.0.1:${port}/mcp`)),fetch(`http://127.0.0.1:${port}/mcp`, {const inflight = fetch(`http://127.0.0.1:${port}/slow`);const response = await fetch(`http://127.0.0.1:${port}/mcp`, {@modelcontextprotocol/client, @modelcontextprotocol/server, pipenet, @eslint/js, @modelcontextprotocol/core, @modelcontextprotocol/node, @modelcontextprotocol/server-legacy, @sebbo2002/semantic-releas
`Access-Control-Allow-Credentials` is omitted whenever the allowed origin comes
[reject the whole CORS response](https://fetch.spec.whatwg.org/#http-access-control-allow-credentials)
Gates applied: no_behavioural_pass.
402713e9bf0efull audit observations/trust-audit/mcp-server/punkpeye__proxy-1.json · Report an issue / request a re-scanAudit history
Every audit this server has had. A grade with a past is a grade somebody is still checking.
| Date | Source | Verdict | Grade | Score | Change |
|---|---|---|---|---|---|
| 2026-10-05 | 402713e9bf0e | CAUTION | B | 80 | first audit |
Questions
What is the Proxy MCP server?
A TypeScript streamable HTTP and SSE proxy for MCP servers that use stdio transport.
What tools does Proxy expose?
1 in total: 1 read-only, 0 that write, and 0 that can delete or overwrite. Every one is listed on this page with its risk.
Is Proxy safe to connect to an agent?
With care. The audit graded it B (80/100) and found 13 things worth knowing before you trust this server, listed below with the exact line each was found on.
What credentials does Proxy need?
No credential environment variables were found in its source, so it appears to need none.
How does Proxy run?
It speaks sse, stdio and streamable-http, so it runs as a local process your client starts. It is published on npm as mcp-proxy at 1.0.0.
How current is this page?
The grade is for one exact copy of the source (402713e9bf0e), read on 2026-10-05. The repository is watched and re-audited when it changes.