Multiple MCP servers or one endpoint: what the tool list costs

Connecting a second and a third MCP server is easy. The cost shows up later, in the context window. At the start of every conversation the client asks each server for its tools (the tools/list call). It hands the model every name, description and input schema it got back. The model reads all of it before your first question.

We measured that cost on 24 September 2026 for three professional data services: Victano (EU public tenders), Rekvira (EU regulation text) and Avokata (Lithuanian law and court rulings). First each one connected directly and signed in, the way a user adds three separate connectors. Then the same three behind Datailo, one hub address.

How big are three tool lists?

Bytes are the size of the serialized tools/list answer each address returned, measured by our capture script. The model’s token count depends on its tokenizer, so we report bytes rather than guess tokens. The ratio is what matters: the direct route loads 7.2 times as much text before any work starts.

The hub’s list does not grow when a service is added. Its 15 tools are the same whether one service is switched on or all three: the services’ own tools are found with datailo_tools and called with datailo_invoke.

What does the hub route cost instead?

The hub route has its own cost. With one hub address the model does not see a service’s input schema up front, so before its first call to a tool it asks for it:

1. datailo_tools with a word such as “ruling” lists matching tools across the services you switched on.
2. datailo_tool_schema returns one tool’s full inputs. For Avokata’s cited_by that answer was 2,724 bytes and took 34 ms.
3. datailo_invoke runs the call. Avokata’s cited_by on Civil Code Article 6.256 returned 2,426 rulings that apply the article, in 7.3 seconds; almost all of that time was Avokata’s own work, not the hub’s.

That is one or two extra round trips per new tool, paid only for the tools the conversation uses. Against 83,616 bytes not loaded, it is usually the better deal. When you use a single service all day, connecting it directly is simpler, and every service keeps its own address for that reason.

When do many MCP servers become a problem?

The pages that rank for this query are mostly people asking how to run several servers at once:

• a Cursor forum thread titled “Multiple HTTP MCP servers in one project: Agent only registers one server”;
• an r/mcp thread on managing many servers across clients;
• a Hugging Face question about hosting several servers on one endpoint.

Our measurement shows where the weight comes from in a real set of three.

Descriptions are the largest part

Victano’s 22 tools take 45,857 bytes because each description explains in detail when to use the tool. That helps accuracy and costs context.

Plumbing repeats

Each of the three services ships its own sign-in tool and its own workflow readers (list_workflows, get_workflow). A client connected to all three shows the model three of each.

Names overlap

Rekvira and Avokata both have a tool called verify_citation, one for EU regulation text and one for Lithuanian law. Through the hub every call names its service, which makes it harder for the model to send an EU citation to the Lithuanian checker.

How we measured

A script opened MCP connections the way a client does. It called tools/list on each service’s own address after signing in with a reserved test address. Then it called tools/list on mcp.datailo.com, then the three hub calls above. Every number on this page is in the recorded run below, with the time each call took. Service tool counts change as the services ship features, so read the figures as a measurement taken on that date.

Related

• How to add an MCP server to Claude: the address, the sign-in and a first answer
• The Datailo catalogue: what each service covers and how fresh its data is
• Connect Datailo in Claude, Claude Code, ChatGPT, Cursor or VS Code