# MCP Inspector (CLI mode) 0.15.0 (Node 20) / 2.12.0 (Node 24): our test log

Canonical: https://theagenticweekly.com/tests/mcp-inspector · Last verified: 2026-10-25 · Published: 2026-10-25 · Author: Agentic Weekly (operated independently from Texas, US) · Evidence: Tested by us on 2026-10-25. Local open-weight model, not the vendor's hosted models. A smoke test on a CPU-only box, not a benchmark.

> MCP Inspector listed the filesystem server's 14 tools from the command line on both 0.15.0 (Node 20) and 2.12.0 (Node 24) in under a second; the 2.x install is smaller.

## Result at a glance

Table: MCP Inspector (CLI mode) test record

| Field | Value |
|---|---|
| Result | Passed |
| Version tested | 0.15.0 (Node 20) / 2.12.0 (Node 24) |
| Date and time | 2026-10-25, 23:29 CDT (America/Chicago) |
| Task | Use the Inspector in CLI mode to connect to the reference filesystem MCP server over stdio and list its tools, on Node 20 (resolving 0.15.0) and Node 24 (resolving 2.12.0). We did not run the browser UI. |
| Model used | none (no language model involved) |
| Hardware | Linux x86_64 virtual machine (Debian 13), 8 vCPU (Intel Xeon, 1 thread per core), 15 GiB RAM, no GPU |
| Install, Node 20 (0.15.0) | 7.2 s, 147 MB, 258 packages |
| Install, Node 24 (2.12.0) | 7.7 s, 109 MB, 140 packages |
| CLI tools/list wall time | 0.85 s (0.15.0) and 0.47 s (2.12.0), one run each |

## What we found

- Both versions printed the same 14-tool list as JSON, so scripted use of --cli --method tools/list works on either.
- Install: 147 MB in 258 packages for 0.15.0 against 109 MB in 140 for 2.12.0.
- Wall times (0.85 s and 0.47 s) include starting both the Inspector and the server and were measured once each with the shell clock, so treat them as rough.

## What we ran, step by step

Table: Commands run, wall-clock time and exit code

| Step | Wall time | Exit code | Notes |
|---|---|---|---|
| npm install on Node 20.19.2 (cold) | 7.2 s | 0 | Resolved 0.15.0; 147 MB in 258 packages; load 3.45. |
| npm install on Node 24.22.1 (cold) | 7.7 s | 0 | Resolved 2.12.0; 109 MB in 140 packages; load 1.73. |
| CLI tools/list on Node 20 / Inspector 0.15.0 | 0.85 s | 0 | 14 tools returned as JSON. |
| CLI tools/list on Node 24 / Inspector 2.12.0 | 0.47 s | 0 | 14 tools returned as JSON; the server printed "No valid root directories provided by client" to stderr, harmless for this call. |

Exact commands (paths shortened)

```
# npm install on Node 20.19.2 (cold)
npm install --no-audit --no-fund --cache /tmp/npmcache @modelcontextprotocol/inspector

# npm install on Node 24.22.1 (cold)
npm install --no-audit --no-fund --cache /tmp/npmcache @modelcontextprotocol/inspector

# CLI tools/list on Node 20 / Inspector 0.15.0
node node_modules/.bin/mcp-inspector --cli node <fs-server-1.0.0> /path/to/root --method tools/list

# CLI tools/list on Node 24 / Inspector 2.12.0
node node_modules/.bin/mcp-inspector --cli node <fs-server-2.0.1> /path/to/root --method tools/list
```

## Raw output (excerpts)

First lines of the Inspector 0.15.0 output

```
{
  "tools": [
    {
      "name": "read_file",
      "title": "Read File (Deprecated)",
      "description": "Read the complete contents of a file as text. DEPRECATED: Use read_text_file instead.",
      "inputSchema": {
        "type": "object",
        "properties": {
          "path": {
            "type": "string"
          },
          "tail": {
            "description": "If provided, returns only the last N lines of the file",
            "type": "number"
          },
          "head": {
```

First lines of the Inspector 2.12.0 output (stderr then JSON)

```
Secure MCP Filesystem Server running on stdio
No valid root directories provided by client
{
  "tools": [
    {
      "name": "read_file",
      "title": "Read File (Deprecated)",
      "description": "Read the complete contents of a file as text. DEPRECATED: Use read_text_file instead.",
      "inputSchema": {
        "type": "object",
        "properties": {
          "path": {
            "type": "string"
          },
          "tail": {
            "description": "If provided, returns only the last N lines of the file",
            "type": "number"
          },
          "head": {
        
```

## Gotchas and things that broke

- Inspector 2.12.0 declares a minimum of Node 22.19; on Node 20 npm silently installs 0.15.0 instead. The command-line flags matched for the call we made but the two versions are different codebases.
- We did not open the browser UI, so authentication tokens, proxy settings and session behaviour of the UI mode are untested.

## What we did not test

- The browser UI, OAuth flows, SSE and streamable HTTP transports.
- Calling tools through the Inspector: only tools/list was run.
- One run each; not a benchmark.

## Reproduce it

Versions change. These commands install whatever is latest on the day you run them unless a version is pinned, so expect different results later. The version we measured is in the table above.

```
npm install @modelcontextprotocol/inspector
node node_modules/.bin/mcp-inspector --cli node /path/to/server.js --method tools/list
```

## How to read this test

Every number on this page was measured on this one machine, which also ran other jobs, so timings are indicative and vary run to run. A pass means our small task worked once or as stated, a fail means it did not work as we ran it; neither says how the tool behaves with a vendor's frontier model, on a GPU, or at scale. Where a tool could not run without an account or a GPU, we say so instead of guessing.

See the [testing rig](https://theagenticweekly.com/methodology#testing-rig) for the hardware, the local model and the rules we follow, and the [test hub](https://theagenticweekly.com/tests) for every other test.

## FAQ

### Can the MCP Inspector be scripted?

Yes: in our run the --cli mode with --method tools/list printed the server's tools as JSON on both 0.15.0 and 2.12.0.

## Sources

- [MCP Inspector repository](https://github.com/modelcontextprotocol/inspector) (fetched 2026-10-25)

## Related

- [All test logs](https://theagenticweekly.com/tests)
- [Methodology and testing rig](https://theagenticweekly.com/methodology#testing-rig)
- [Study: MCP server startup and call latency over stdio](https://theagenticweekly.com/research/mcp-servers-latency-and-failures)
- [Study: the silent version downgrade on older Node, and other install traps](https://theagenticweekly.com/research/older-node-silent-downgrades)

## How to cite

Agentic Weekly, "MCP Inspector (CLI mode) 0.15.0 (Node 20) / 2.12.0 (Node 24): our test log", last updated 2026-10-25, https://theagenticweekly.com/tests/mcp-inspector