Langflow MCP client: add Sume's hosted MCP server

Langflow is an MCP client through its MCP Tools component: register the server under Settings > MCP Servers > Add MCP Server, drag it from the MCP sidebar onto the canvas, enable Tool mode, and connect the component's Toolset port to an Agent's Tools port. For Sume's hosted MCP server, choose HTTP/SSE, enter https://mcp.sume.com/mcp, and add an Authorization header whose value is a Credential global variable holding Bearer and your Sume API key.

Langflow's side comes from Use Langflow as an MCP client, the page for Langflow 1.12.x; Sume's side comes from MCP OAuth and API keys, MCP tools and gates, and Jobs and results, all read on 2026-09-28. Sume has no official Langflow integration: Langflow connects to Sume's remote MCP server like any other, and Sume's basics page says hosted MCP still works but is not part of the primary path today. Langflow can also act as an MCP server for its own flows; this post covers the client side. n8n MCP Client Tool with Sume covers another visual builder.

How do I add an MCP server in Langflow?

As of Langflow 1.9.x, MCP Tools is not a draggable component under Agents, so you register the server first. On 1.12.x:

• Store the key. Click your profile icon, then Settings, then Global Variables, and create a Credential variable such as SUME_BEARER. Its value must include the Bearer prefix with a space, followed by your Sume API key.
• Register Sume. Open Settings > MCP Servers and click Add MCP Server, or click MCP in the flow editor's left sidebar and then Add MCP Server. Choose HTTP/SSE and enter the Name sume, the Streamable HTTP/SSE URL https://mcp.sume.com/mcp, and one header: key Authorization, value SUME_BEARER. When the connection succeeds, Langflow shows how many tools the server exposes.
• Drag the new server from the MCP sidebar onto the canvas. That adds an MCP Tools component for it.
• In the component's Tool field, pick one Sume tool, or leave it blank for all of them.
• Enable Tool mode in the component's header menu, then connect its Toolset port to the Agent's Tools port. Attach Chat Input and Chat Output to the Agent if the flow lacks them.
• Open the Playground and enter a prompt that uses the tool you connected.

Which Sume tools should each MCP Tools component serve?

One each. A blank Tool field gives the agent every tool the server offers, and an API-key session sees Sume's full hosted tool set, paid tools included. Langflow's MCP client page describes no approval step before the agent calls a tool, so an agent holding every tool can start paid jobs on its own judgment. Langflow's docs say to add more tools components for more tools: give each one a single Sume tool and connect every Toolset to the Agent.

Sume's paid tools each need an idempotency_key; dry_run=true previews admission and cost without submitting; max_spend_usd caps a call only when it is sent. The agent writes those arguments, so they are not a limit your flow enforces. Hosted MCP also cannot read files from your laptop.

Will a long Sume render time out in Langflow?

Langflow's MCP client page documents no tool-call timeout, and Sume doesn't hold one call for a whole render. jobs_wait returns after at most 55 seconds per call; on wait_slice_expired the agent should call it again with the same ids and never resubmit the paid create. MCP tool call timeouts on long-running video jobs has the pattern.

What if the Sume server won't connect?

• Langflow resolves the global variable to its value before it calls the server and passes that value without validating it, so a wrong key shows up only when Sume rejects the call.
• Headers set on an MCP Tools component take precedence over the server's headers. Keep one key header, not two.
• verify_ssl defaults to true; leave it on.
• If an administrator has locked MCP server management, adding a server shows a locked message.