Registering a Streamable HTTP MCP server with no authentication, then allowlisting a tool, fails with "We couldn't allowlist the tools due to an internal error: <id> (1360387860)". The tool selection resets and no agent action is created.
The trigger is any parameter whose `type` is a list, even a plain nullable one. A parameter with `"type": "string"` allowlists fine. All of these fail: `["null","string"]`, `["null","array"]`, `["null","integer"]`, `["null","boolean"]`, and `["null","string","integer"]`.
The server answers `initialize`, `notifications/initialized` and `tools/list` correctly before the error. A tool with the same description and plain types passes, so it isn't the description length. Type lists are valid JSON Schema, and many servers emit `["null", X]` for optional fields automatically (Go's schema generator does), so this will hit a lot of servers.
Expected: the tool imports, or the error says which schema was rejected. The Considerations for MCP for Agentforce page says tool schemas that don't map to Lightning types still work, only without variable storage.
Repro: one tool with one optional parameter `{"type": ["null","string"]}`. Developer Edition org created 2026-10-28. Setup > Agentforce Registry > Register MCP Server > No Authentication > Create and Continue > Add Tool > Allow and Continue.
Workaround: allowlist only tools whose parameters have a single plain type.
Related: Known Issues has an entry, "Adding an MCP tool fails when its schema includes both a default value and unevaluatedProperties: false" (Service/Agentforce, Solution in Progress), which shows the same kind of "internal error" on save. My schema has neither keyword, so this looks like a separate trigger, but it may share the schema-import step.
#Agentforce #Mcp
