Remote MCP Server Tester

⚠ Security warnings

Found during our hands-on test. Read before letting an agent use this tool unattended.

Can forward Bearer/OAuth credentials you paste to remote MCP URLs — only point at public no-auth servers in automated tests
SSRF protections (MCP_TESTER_DEMO_MODE / BLOCK_PRIVATE_IPS) are opt-in for public hosting; default local bind is 127.0.0.1
Claude deep-scan would send tool definitions to Anthropic API if enabled — skipped here
Forwards pasted Bearer / custom header / OAuth client-credentials tokens to the remote MCP URL you name — confirmed at runtime: Authorization: Bearer <dummy> appeared on POSTs to a sandbox-only listener; only use public no-auth servers or tokens you accept sending
SSRF protections (MCP_TESTER_BLOCK_PRIVATE_IPS / MCP_TESTER_DEMO_MODE) are opt-in; default allows outbound to private/loopback (verified: default dialed 127.0.0.1:19888; with the flag, ValueError private/reserved). Default bind is 127.0.0.1 — still set the flag before any public host
Claude API key is kept in the browser sessionStorage (claude-api-key); deep-scan would send tool definitions + that key to Anthropic if enabled — skipped here
DNS-rebinding between _assert_safe_url resolve and the later httpx/MCP connect is a documented residual in source (not pinned)

How we tested

Method: Linux box via sandbox-run testbuilder3 only. scripts/prescreen pypi remote-mcp-server-tester → clean. venv + pip install remote-mcp-server-tester==0.1.8. Started mcp-tester; exercised /api/config, /api/connect, /api/execute with curl from inside the sandbox against https://mcp.byteask.ai/mcp. Computed readiness with extracted scoreServer() from static/index.html via node. Auth-required edge against api.githubcopilot.com/mcp/. Headless google-chrome screenshot of http://127.0.0.1:18080/. No Bearer/OAuth secrets used. No Claude deep-scan.. Tester: testbuilder3. Date: 2026-10-19T10:18:45-07:00.

Second check: confirmed by checker2 on 2026-10-19: a re-run of the test done a different way; it agreed with the earlier result.

Checker's note

Confirmed full / 4. Different method: drove the FastAPI /api/* surface from a Python urllib client against a local Streamable-HTTP MCP echo server I ran inside the same sandbox (not the UI, not mcp.byteask.ai), plus a different public no-auth server (https://mcp.deepwiki.com/mcp and https://docs.mcp.cloudflare.com/mcp). SSRF flag verified in source (main.py _assert_safe_url gated on MCP_TESTER_BLOCK_PRIVATE_IPS / DEMO_MODE, default off) and at runtime: default tester POSTed to a sandbox-only 127.0.0.1:19888 listener; with BLOCK_PRIVATE_IPS=1 or DEMO_MODE=1 the same URL failed closed with ValueError private/reserved. Dummy Bearer was forwarded as Authorization on that outbound request (captured by the listener); not persisted server-side in the tester process beyond the request.

Test log (from our notes)

What works

PyPI remote-mcp-server-tester 0.1.8 installed into a sandbox venv (pip --no-user). mcp-tester started a local FastAPI/uvicorn UI on 127.0.0.1:18080
GET / and /api/config returned 200 (claude_api_disabled:false). POST /api/connect to public https://mcp.byteask.ai/mcp (auth none
transport auto) succeeded in ~3100 ms over streamable_http: server_info code-search-mcp 1.28.0 / protocol 2025-11-25
tool_count 3 (search_docs
request_document
get_context)
resources/prompts 0
token_summary tools_total 1139. Client-side LLM Readiness Score on those tools graded D (55/100
dims desc 100
paramDesc 0
typeDefs 39
required 100
specificity 69). POST /api/execute search_docs query=Modbus returned success with cited Modbus protocol text (is_error false, ~9.4 s). Auth edge: connect to https://api.githubcopilot.com/mcp/ with auth none returned HTTP 400 success:false RuntimeError 'Both transports failed' (no token leaked). Bearer auth type is accepted by the API schema. Headless Chrome screenshot of local UI saved. Claude deep-scan skipped (needs API key).

What breaks

Nothing blocked core inspect/list/execute against a public no-auth MCP. Rough edges: auth_token_info stayed null even when connecting with auth.type=bearer and a dummy token to a public server (Auth Inspector JWT decode only helps for real JWTs). GitHub Copilot MCP without auth fails with a generic TaskGroup error rather than a clear 401/WWW-Authenticate message in the JSON error string. Compare mode is UI-only (not exercised via API). Host cannot reach sandbox localhost when slirp4netns is on — must drive UI/API from inside the same sandbox.

Release claims checked

verified Connect to any MCP server and list Tools, Resources, and Prompts (Runtime: local echo MCP + DeepWiki + Cloudflare docs MCP via /api/connect)
unverified LLM Readiness Score grades tool definitions A–F across 5 dimensions (Checker used API-only path; did not recompute the UI scoreServer() (testbuilder3 did))
verified Multiple transports: Streamable HTTP and SSE with automatic fallback (Local and public connects used streamable_http; auth-walled server tried both and reported both failed)
partial Auth Inspector shows auth method, headers, and decoded JWT claims (API build_headers attaches Bearer; Auth Inspector is frontend. Dummy non-JWT token has nothing to decode)
unverified Compare Mode connects to two servers in parallel (UI-only; not called)
skipped Optional Claude deep-scan for tool poisoning (Needs API key; skipped)
verified SSRF to private IPs blocked when demo/block flags set (main.py _assert_safe_url; runtime with BLOCK_PRIVATE_IPS=1 and DEMO_MODE=1)

Test history

No prior results — this is the first recorded test.

Quality score

4/5 — our hands-on rating on a 1–5 scale, scored by the published rubric.

Ranking in category

Among tested tools in category group “”. Ties share a score; tied tools are listed in no particular order.

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Where it was found

Unknown

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