How to connect Claude to your construction accounting data

Most contractors already know what they would ask an assistant: which jobs are over budget, who has not been paid, what is committed against each job. The answers sit in an accounting or job-cost system that Claude cannot see. This guide walks through connecting the two, in the order that avoids the usual mistakes.

What you need before you start

• An MCP server for your system. MCP, the Model Context Protocol, is the open standard Anthropic introduced in November 2024 for connecting AI assistants to data sources. Claude speaks MCP; your accounting system does not, so something has to translate.
• A Claude plan that allows custom connectors. Anthropic's help article says custom connectors work on Free (limited to one), Pro, Max, Team and Enterprise plans. On Team and Enterprise an Owner adds the connector for the organisation first.
• A login that can only read. Whatever sits between Claude and your database or API should use credentials that cannot write, so a mistake in the connector cannot change a ledger.
• Three questions you can check. Pick three numbers you already trust from a report you run today. You will use them to test the answers.

Step 1: Decide where the data lives

How you connect depends on where the system runs, so settle this first.

Step 2: Put an MCP server in front of it

You have three routes. Build one yourself, which suits a team with spare engineers and a single system. Use the vendor's own MCP server where one exists: several vendors now offer one, and our systems list marks them. Or use a connector that already handles the construction systems and their quirks, which is what Junction is for.

Whichever you pick, ask the questions in our MCP security checklist before you connect anything with real data.

Step 3: Add the connector in Claude

These are the steps from Anthropic's help article for custom connectors using remote MCP. The menu names change over time, so check the current article if something differs.

1. Open Customize, then Connectors.
2. Click + Add, then Add custom connector.
3. Enter a name and your server's remote MCP URL, then Continue.
4. Review the detected sign-in settings and change them if you need to, then Continue.
5. Choose how people sign in: Sign in now, Sign in when needed or No sign in.
6. Click Add. To use it in a chat, click + in the lower left, choose Connectors and switch it on.

On Team and Enterprise plans an Owner first adds the connector under Organization settings, Connectors. Members then click Connect in their own settings.

Step 4: Test with answers you already know

Ask the three questions you chose and compare the answers with your own report to the dollar. Check that the answer says which system it came from and how fresh the data is. If a number is off, find out why before anyone else relies on it: a different job status filter or a cut-off date is the usual cause.

Step 5: Keep it safe

Anthropic's own guidance for custom connectors is worth reading in full. Its main points:

• Custom connectors are not verified by Anthropic, so only connect to servers you trust.
• Review the permissions requested when you sign in, and limit them where you can.
• Watch for prompt injection: hidden instructions inside data can try to steer the assistant. Built-in protections help but do not fully prevent it.
• Disable tools you do not need, and only choose "Allow always" for tools you trust.
• Server behaviour can change, so keep an eye on tool activity.

For accounting data, add two rules of your own. Exclude payroll and personal records unless a person has a clear reason to see them, and give each person only the systems and jobs they work on.