Does a SaaS with a full web UI still need an MCP App?

A link and an MCP App solve different problems. A link sends the person out of the conversation: they look at your page, and the assistant has no idea what they saw, clicked or changed. An MCP App puts a small view inside the conversation, and the assistant can read its state and react to it. The view is shared between the person and the model, which a browser tab is not.

So the question is whether the task needs that loop. If the job is "show me this month's chart", a link or a plain tool result is enough and much cheaper to build. If the job is "let me adjust these filters, then have the assistant explain what changed and draft the email", an inline view saves the person from copying things back and forth.

You should not rebuild your product in the MCP layer. Pick one or two moments where people currently leave the chat, act in your app and come back to paste the result, and build small views just for those. Keep the full product where it is and link to it for everything else.

Lower token use is a real side effect, because what the person does in the view does not all have to pass through the model, but on its own it rarely justifies a second interface to maintain. Start with plain tools, watch where users get stuck, and add a view only where the round trip hurts.

Listings mentioned

• Creating MCP Apps · skill by alpic-ai
  Walks through building an MCP App from spec to deploy, and starts from the point that the view is shared by the person and the model.
• MCP builder · skill by anthropics
  Anthropic's guide to designing plain MCP tools well, the right first step before deciding any view is needed.

Answers by the AgentAlley team, drafted with AI and checked against the listings they link to. Not a real-person reply from the original thread.