Claude in Excel with MCP Connector - Talk to Your Backends from Inside Excel

Published: February 20, 2026

Claude in Excel can now connect to your backend APIs through MCP. That changes things quite a bit.

I ran a whole bunch of tests across my MCP connectors. And it works. Really well actually. Once you connect the MCP server in Claude AI Settings → Connectors → Custom Connectors, Claude in Excel just picks it up and talks to it. You ask in natural language, it hits the backend, brings back results. Like having a ChatGPT-style interface sitting right inside Excel but connected to your own stuff.

Quick context on my setup

A lot of my client work runs on reusable FastAPI backends - data pulls from databases, processing, PDF report generation, some AI based, some just regular Python automations. These backends always need a front end. I use Custom GPTs, React UIs, or xlwings Lite depending on the situation. Claude in Excel with MCP is now one more option. And a pretty good one.

And by the way - a reality check here. I work with small businesses. Yes I have multi-agent setups that do all kinds of AI and data science gymnastics. But my bread and butter is automation work with operations, finance and marketing teams. Some need LLM API calls, some don't. And this is where tools like xlwings Lite, Custom GPTs and now Claude with MCP make a big difference in actual day to day work.

What I actually tested

Test 1: I connected my YFIN MCP connector that pulls data from Yahoo Finance. Had it pull price data for the last 3 years. Then had Claude in Excel build a 30-day rolling returns model on that data, compute averages, confidence intervals, and create validation sheets. It did all of this properly - the scenario modeling, sub-scenarios, validation formulas. This is where Claude in Excel is genuinely strong.

Test 2: I have a Technical Analysis MCP server. I asked Claude in natural language to generate a technical analysis report for a specific security. It connected to the backend, the backend generated the PDF and HTML reports, and Claude shared the URLs back. Matter over.

Test 3: Same thing with my Security Performance Review server - asked it to run a multi-security risk-returns comparison. Backend generated the HTML report with charts and CSV outputs for offline validation. URL came back right in the Excel chat.

So three different MCP servers, three different types of backend operations - data pulls, report generation, multi-security analysis. All worked through natural language from inside Excel.

Where it stumbles

The data writing part. If I ask it to pull thousands of records from a backend it gets into trouble. Not the data pull itself - that works fine. Two issues: one, the whole dataset goes into its context window so there's context bloat. Two, writing large data to Excel cells - it is still not good at it. Left to its own devices it thinks it is Claude Code - tries to pull everything at one shot, write everything at one shot, then chokes up and collapses.

The fix is simple enough - I guide it to download data in smaller chunks and write using its office.js tools. Then things go smoothly. But you have to tell it, it won't figure this out on its own.

Also - URLs. If the backend shares a URL (like a PDF report link), Claude can share that URL with you but it cannot fetch or open the URL itself. Which is fine for my use case - I just want the URL, I'll open it myself. But good to know.

My public MCP servers - free to use

I have published three open source MCP servers. All are public endpoints, free to use. I have rate limits at backend but no access controls.

▸ YFIN Server - pulls price data, financial statements, quarterly results, market data from Yahoo Finance

▸ Security Performance Review (SPR) - compares multiple securities across risk-returns metrics, drawdown analysis. Generates HTML reports with charts plus CSV outputs for offline validation

▸ Technical Analysis Server - takes a security and date range, creates daily and weekly technical analysis charts, sends it to an AI for intelligent interpretation, and returns the report as PDF and HTML

Connect them via Claude AI → Settings → Connectors → Custom Connectors → plug in the MCP server URL. Documentation and source code links below.

One important note on MCP security

I tell my clients - don't touch any unknown MCP server. They can be genuinely dangerous. You are basically running somebody else's code blind. You never know what an unknown MCP endpoint is actually doing with your data or your system.

My servers are documented, open source, and you can inspect every line of code. If you are not comfortable using my endpoints directly, take the source code, scan it, make any changes you want, and deploy on your own infrastructure. That is the right way to approach any MCP server you don't control.

Which tool for which job

This is how I think about it now:

▸ Claude in Excel (native) - for all Excel work. Models, scenarios, complex formulas, validation sheets, lightweight Python. Just this use case alone makes it worth it.

▸ Claude in Excel + MCP - to connect to your backend for natural language queries and light automations. E.g. "pull portfolio analysis for this date range" or "generate customer statement for this ID"

▸ Custom GPT connected to same backend - natural language interaction not requiring Excel. E.g. generate a customer statement PDF and give me the URL.

▸ xlwings Lite - heavy Python in Excel work, advanced automations, and Excel apps where you specify parameters in a controls sheet to run automated processes.

▸ Claude Code - offline Python and JavaScript work, full stack apps, tools, heavy automations.

Coming next

I want to validate the rolling returns model from Test 1 using Claude Code with offline Python and then use xlwings Lite to build the chart. So it becomes a full example of using the right tool for each step - Claude in Excel for the model, Claude Code for validation, xlwings Lite for the final output. That will be a separate post.

Resources

Claude in Excel help pages (well written, check them out)

MCP Server Documentation and Source Code:

Previous Claude in Excel posts: