Feat/cli http

[ryanjclark]

This feature introduces streamable http support for the CLI mode. It is backward compatible; the default transport is sse. There is a new flag for --transport. Otherwise, the transport will be inferred from the suffix of the url (/mcp or /sse).

Motivation and Context

The CLI lags behind the client for Streamable HTTP support.
Closes #410

How Has This Been Tested?

# http
node build/cli.js --cli http://0.0.0.0:8001/mcp --method tools/list # success
node build/cli.js --cli http://0.0.0.0:8001/mcp --method tools/list --transport http # success
node build/cli.js --cli http://0.0.0.0:8001 --method tools/list --transport http # success
node build/cli.js --cli http://0.0.0.0:8001 --method tools/list # SSE error

# sse
node build/cli.js --cli http://0.0.0.0:8001/sse --method tools/list # success
node build/cli.js --cli http://0.0.0.0:8001/sse --method tools/list --transport sse # success
node build/cli.js --cli http://0.0.0.0:8001 --method tools/list --transport sse # success
node build/cli.js --cli http://0.0.0.0:8001 --method tools/list # success

Breaking Changes

No breaking changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[ryanjclark]

I am unsure how maintainers want this tested. It seems like cli/scripts/cli-tests.js doesn't work and isn't used.

[olaservo]

Hi, sorry I missed your question about the test script. This test doesn't run on CI yet, so there might be something that broke the CLI test script.

I was able to run the cli\scripts\cli-tests.js if I changed this part starting on line 64:

// Create a temporary directory for test files
const TEMP_DIR = path.join(os.tmpdir(), "mcp-inspector-tests");
fs.mkdirSync(TEMP_DIR, { recursive: true });

[ofek]

We are also very interested in this feature internally as we only support this transport type for development tools.

[ryanjclark]

We are also very interested in this feature internally as we only support this transport type for development tools.

Hey Ofek, us too. I will work on this now.

[ryanjclark]

Added tests for http transport. The SSE transport on server-everything times out after every request, making it weird to test. I figured it was fine to include in tests because it is deprecated.

[olaservo]

Looks good to me, just need to run this to fix formatting check failure in CI:

npx prettier --write cli/scripts/cli-tests.js

[olaservo]

Thanks!

[ofek]

Thanks! When might this be released?

[olaservo]

@ofek I will create one today, there might be an unrelated bug fix we want to get in as well, but if not we can just release what is here now.

[ofek]

Thanks! It looks like the release needs manual intervention: https://github.com/modelcontextprotocol/inspector/actions/runs/15891752275

[olaservo]

Hi @ofek , yes someone from the core maintainers team needs to approve that part. Will keep you posted.

[ofek]

No worries! How long does that usually take?

[olaservo]

@ofek usually its only around 1 working day or so, I think it flew under the radar this time. But it should be live now: https://www.npmjs.com/package/@modelcontextprotocol/inspector?activeTab=versions

[pztrick]

i've added a very small p/r #578 that allows other paths that do not necessarily end in /mcp like /mcp/http.