MCP connections
Connect external tool servers and diagnose authentication or discovery problems.
In this topic
An MCP service supplies tools an agent can call: search a tracker, inspect a repository, or retrieve documents. A model provider supplies inference. Configure each in its own area; adding a model endpoint does not import the service's tools.
Add and verify a service
Open Tools & MCP → Services and choose Add Service. Select a supported catalog entry or configure a custom server. Check the transport and complete the authentication method requested by that server. HTTP services need a complete MCP endpoint; local stdio services need the command and environment supported by their execution path.
Use the connection test, save the entry, and inspect the discovered tool count. Then make a small read-only call with an agent allowed to use that service. Successful discovery establishes that schemas were retrieved, not that every tool has permission to read every resource.
Connection settings
| Setting | Meaning |
|---|---|
| Name | Identifies the service in Mellow and helps distinguish its tools |
| Endpoint or command | Where the MCP transport connects |
| Authentication | OAuth, a token, custom headers, or no authentication according to the service |
| Enabled | Whether Mellow may use this connection |
| Auto-connect | Whether connection is attempted when Mellow starts |
| Discovery timeout | How long catalog discovery may wait |
| Tool-call timeout | How long an individual operation may wait |
Store tokens and secret headers in the secure fields. Do not include them in a service name, URL query, or copied diagnostics. OAuth sign-in must complete for the service and account you intend to use.
Discover and select tools
Mellow requests the server's tool list and registers a namespaced catalog. A server named research exposing search can appear as research_search; inspect All Tools for the actual exposed name. Namespacing distinguishes identical operation names from different services.
A refreshed catalog replaces the prior catalog as a complete set. The server's advertised count is not the number of all local capabilities. An MCP server with five tools can be functioning normally; what matters is whether those five are the intended operations.
Tool availability also depends on the current agent and request. Built-in protected tools cannot be replaced by a server using the same name. When names are ambiguous, choose the explicit exposed name rather than relying on a bare alias.
What a call sends
The agent supplies arguments under the discovered schema. Mellow routes the call to the owning service and returns the result to the agent. The remote service receives the arguments and operates under the configured credentials; it does not gain implicit access to every local file.
Results may include sensitive information. They can become context for the model handling the conversation. Consider both the tool service and the selected model provider when deciding whether a task is appropriate.
For clients integrating with Mellow itself, the local HTTP bridge includes GET /mcp/tools and POST /mcp/call. Use the configured Mellow server address and authentication; these convenience endpoints are not a universal replacement for an MCP server's own transport protocol.
Diagnose the correct layer
| Failure | Inspect next |
|---|---|
| Connection refused | Process health, host, port, and network route |
| Authentication rejected | Account, token expiry, OAuth scope, and required headers |
| Discovery timeout | Server response and discovery budget |
| Connected, zero tools | What that account's server actually advertises |
| Tool listed but execution denied | Resource permissions and Mellow's tool policy |
| Schema error | The operation's argument schema and provider compatibility |
| A previously available tool disappeared | Updated catalog and the selected connection |
Use Test Connections, Reconnect All, and Copy Diagnostics where shown in the Services menu. Review Insights for the failed operation and transport. Reconnecting cannot fix a missing role or malformed server schema.
Maintain a connection
Disable a service to stop using it without discarding its settings. Remove it when it is no longer needed, and revoke the grant on the provider when appropriate. Review discovery after service upgrades; names and schemas can change independently of Mellow.
For a Cloud workspace, begin with its dedicated sign-in flow so the saved connection is bound to the verified account and workspace.
Continue exploring · Connect your workspaceImporting plugin packages →Understand which package components Mellow can use and what needs separate setup.