fix(mcp): OpenAPI tool listing and execution for relative URLs and camelCase

[Sameerlite]

Summary

Fixes two issues with OpenAPI-based MCP servers (e.g. Petstore, fusion_litellm_mcp):

Issue 1: Tool Listing Failure (Case-Sensitivity Bug)

Problem: Servers with allowed_tools configured returned 0 tools when the OpenAPI spec used camelCase operationIds (e.g. addPet, updatePet).

Root Cause:

• OpenAPI operationIds are lowercased during tool registration (addPet → addpet)
• allowed_tools contained original camelCase names from the spec
• Filter comparison was case-sensitive, filtering out all tools

Fix: Modified _tool_name_matches() in server.py to perform case-insensitive comparison.

Issue 2: Tool Execution Failure (Relative URL Bug)

Problem: Tool calls failed with InvalidURL: /api/v3/pet for specs with relative server URLs.

Root Cause: Petstore and similar specs have servers: [{"url": "/api/v3"}] - a relative path. The code returned this directly instead of resolving to a full URL.

Fix: Modified get_base_url() in openapi_to_mcp_generator.py to detect relative URLs and derive the full base URL from spec_path (e.g. https://petstore3.swagger.io/api/v3).

Test Coverage

• test_tool_name_matches_case_insensitive - Core matching logic
• test_filter_tools_by_allowed_tools_case_insensitive - End-to-end filtering with camelCase
• test_filter_tools_by_allowed_tools_no_filter - Servers without filters return all tools

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Project	Deployment	Actions	Updated (UTC)
litellm	Error		Mar 10, 2026 6:06am

[greptile-apps]

Greptile Summary

This PR fixes two bugs in the OpenAPI-based MCP server integration: (1) tool listing silently returning zero results when allowed_tools used camelCase operationIds while registered tool names were lowercased, and (2) tool execution failing with InvalidURL for OpenAPI specs that declare a relative servers[0].url (e.g. Petstore's /api/v3).

• Case-insensitive matching (server.py): _tool_name_matches() now lowercases both the incoming tool name and the filter list before comparison. The fix is correct and naturally extends to disallowed_tools as well, though the PR description does not mention this side effect.
• Relative URL resolution (openapi_to_mcp_generator.py): get_base_url() now detects a relative server_url and derives the full URL from the spec_path domain. The logic handles HTTP/HTTPS spec paths correctly; local-file spec paths with a relative server URL remain unresolved (acceptable limitation with no available domain).
• Test coverage (test_mcp_server.py): Three new unit tests cover the case-insensitive matching fix end-to-end. No tests are added for the get_base_url relative URL fix, leaving that code path without automated verification.
• urlparse is imported inside the function body in get_base_url() rather than at the module top alongside the existing from urllib.parse import quote.

Confidence Score: 4/5

• PR is safe to merge; both fixes are scoped to the experimental MCP server module and carry low regression risk.
• Changes are confined to a clearly experimental module, the logic is straightforward, and the case-insensitive matching fix is well-tested. The relative URL fix lacks a dedicated unit test, but the fix itself is simple URL parsing with no side effects on other code paths.
• No files require special attention; the missing get_base_url test is the only gap worth addressing before merge.

Important Files Changed

Filename	Overview
litellm/proxy/_experimental/mcp_server/openapi_to_mcp_generator.py	Adds relative URL resolution in get_base_url() by parsing the domain from spec_path when the OpenAPI servers[0].url is a relative path. Logic is correct; minor style issue with urlparse being imported inside the function body rather than at the module top.
litellm/proxy/_experimental/mcp_server/server.py	Makes _tool_name_matches() case-insensitive by lowercasing both the tool name and filter list before comparison. The change correctly fixes OpenAPI camelCase operationId mismatches and also implicitly applies to disallowed_tools. Minor performance overhead from rebuilding the lowercase list on every call.
tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server.py	Adds three pure unit tests covering case-insensitive tool name matching. No real network calls are made. Missing a corresponding unit test for the get_base_url relative URL fix.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[get_base_url called] --> B{spec has servers?}
    B -- Yes --> C[read servers 0 url]
    C --> D{url starts with /\nAND spec_path given?}
    D -- Yes --> E{spec_path is http/https?}
    E -- Yes --> F[urlparse spec_path\nextract scheme + netloc]
    F --> G[return domain + server_url\ne.g. https://petstore3.swagger.io/api/v3]
    E -- No --> H[return relative server_url as-is\nInvalidURL still possible for local files]
    D -- No --> I[return server_url as-is\nabsolute URL]
    B -- No --> J{spec has host?}
    J -- Yes --> K[build URL from scheme+host+basePath\nOpenAPI 2.x]
    J -- No --> L{spec_path is http/https?}
    L -- Yes --> M[strip known suffixes\nreturn derived base URL]
    L -- No --> N[return empty string]

    subgraph _tool_name_matches fix
        P[tool_name + filter_list] --> Q[lowercase both]
        Q --> R{tool_name.lower in filter_list_lower?}
        R -- Yes --> S[return True]
        R -- No --> T[strip server prefix\ncheck unprefixed.lower]
        T --> U{match?}
        U -- Yes --> S
        U -- No --> V[return False]
    end

Loading

_{Last reviewed commit: db99fde}

[greptile-apps]

Import inside function body

urlparse is already available in the same urllib.parse namespace used at the top of this file (line 11 imports quote from there). Moving this import to the module level avoids the repeated import resolution on every code path that hits this branch and keeps the import conventions consistent with the rest of the file.

Suggested change

	from urllib.parse import urlparse
	from urllib.parse import urlparse, quote

Or better, just add urlparse to the existing top-level import:

# line 11 — change to:
from urllib.parse import quote, urlparse

and remove the inline import entirely.

[greptile-apps]

filter_list_lower rebuilt on every call

filter_list_lower is reconstructed as a list on every invocation of _tool_name_matches. Since filter_tools_by_allowed_tools calls this function in a loop over all tools, the filter list is lowercased once per tool rather than once per filtering pass. Using a set also changes the in membership test from O(M) to O(1):

Suggested change

	# Normalize filter list to lowercase for case-insensitive comparison
	filter_list_lower = [f.lower() for f in filter_list]
	if tool_name.lower() in filter_list_lower:
	return True
	# Check if the unprefixed name is in the list
	# Check if the unprefixed name is in the list (case-insensitive)
	unprefixed_name, _ = split_server_prefix_from_name(tool_name)
	return unprefixed_name in filter_list
	return unprefixed_name.lower() in filter_list_lower
	filter_list_lower = {f.lower() for f in filter_list}
	if tool_name.lower() in filter_list_lower:
	return True
	# Check if the unprefixed name is in the list (case-insensitive)
	unprefixed_name, _ = split_server_prefix_from_name(tool_name)
	return unprefixed_name.lower() in filter_list_lower

A more impactful refactoring would be to compute filter_list_lower once in filter_tools_by_allowed_tools and pass it through, but the set change above at least removes the repeated list construction.

[greptile-apps]

No test for get_base_url relative URL fix

The PR adds test coverage for the case-insensitive matching fix (_tool_name_matches, filter_tools_by_allowed_tools) but does not include a test for the get_base_url relative URL fix — the other half of the changes described in the PR description. Per the project's custom rule, fixes should include passing tests as evidence. A unit test exercising the new branch would look like:

def test_get_base_url_resolves_relative_server_url():
    """Test that get_base_url resolves relative server URLs using the spec_path domain."""
    from litellm.proxy._experimental.mcp_server.openapi_to_mcp_generator import get_base_url

    spec = {"servers": [{"url": "/api/v3"}]}
    spec_path = "https://petstore3.swagger.io/api/v3/openapi.json"
    result = get_base_url(spec, spec_path)
    assert result == "https://petstore3.swagger.io/api/v3"

def test_get_base_url_absolute_server_url_unchanged():
    """Test that get_base_url returns absolute server URLs as-is."""
    from litellm.proxy._experimental.mcp_server.openapi_to_mcp_generator import get_base_url

    spec = {"servers": [{"url": "https://api.example.com/v1"}]}
    result = get_base_url(spec, spec_path=None)
    assert result == "https://api.example.com/v1"