AI native
Your Claude does the work, and your firm holds the controls
Connect your own Claude to Mastro and it works in your clients' books as you, with exactly your access. Your firm decides, area by area, what it does on its own, what waits for a person, and what it can't touch.
AI native
Whatever you can do in Mastro, your Claude can do
Mastro is built so that anything a person sees or does, Claude can see and do through Mastro's MCP server, as that person. Only what's yours alone to give stays with you: your sign-in factors, your signature, and approving what Claude asked first about.
It works as you
You sign in to Mastro from Claude on the web, on your desktop, or in Claude Code. Claude never sees your password, and every request runs with your permissions: the clients you can see, and nothing more.
It does the work, not just the talking
Categorize a month of bank lines, post the entry that closes it, reconcile an account, send an invoice, ask a client a question, run a pay run, or read a report: the same actions Mastro's screens call, checked by the same database.
It knows the books
Mastro hands Claude a live map of the client's books: the accounts, contacts, feeds, rules, and documents your question names, their balances for the period you ask about, what's waiting, and where the close stands.
Mastro's own screens come with it
In Claude on the web or desktop, the review queue, a reconciliation, and the month-end close open in the chat, and the approve and close buttons are yours.
On your own Claude plan
Mastro never resells AI and never marks up tokens. Each person uses the Claude plan they already have, and another app that speaks MCP can connect the same way.
Safe for a CPA firm
The firm sets the limits, and everything is on the record
A CPA firm answers for its clients' books. These hold whatever Claude is asked.
- The firm sets each areaPosting, rules, invoices and bills, reconciling and closing, payroll, taxes, what goes to clients, lists and client settings, QuickBooks, the team, and plans: for each, Claude does it, asks first, or can't.
- Asking first means a person approvesThe change waits in one AI review queue with its reason. Approving it is always someone's click, and it's made as the person who approves.
- Every action is in the activity feedWhat Claude reads, suggests, and does is in the client's activity feed, marked as Claude's, beside what people did.
- No model runs on the booksMastro runs no AI model of its own. Rules are versioned and deterministic, so the same books and rules always post the same way.
- Sensitive numbers stay maskedSocial Security numbers, bank account numbers, and card numbers reach Claude as their last four digits. Employees' pay rates, withholding, and home addresses never reach it.
- The client's choice, client by clientThe AI module is on a client's plan or it isn't. Claude reaches nothing of a client without it.
- Closed months stay closedClaude works through the same locks as a person. Posted entries never change, and a correction is a reversing entry.
- Every connection is the person's to endEach person sees their connections to Claude in Settings and ends any of them.
Three settings, for each area
Does it, asks first, or can't
- Does it
Claude makes the change
It's made as the person, and it's in the client's activity feed.
- Asks first
A person approves
The change waits in AI review. Whoever approves it makes it, as themselves, one at a time or many at once.
- Can't
It's done in Mastro
Claude is told to do that in Mastro instead, and does the rest.
What a firm asks for
The month, kept by Claude, approved by you
- Categorize
New bank lines
A category for each line no rule covers, from the client's chart and how its past lines went, with the reason.
- Follow up
Questions that wait
A few friendly lines drafted to the client, sent from you only when you approve them.
- Close
Month-end prep
What's left before the close, what looks unusual against last month and last year, and a summary for the client.
- Ask
Questions about the books
Balances, reports, and where the close stands, answered from the books with where each number comes from.
Questions
AI in Mastro, asked
Which AI is it?
Claude, by Anthropic, on each person's own Claude plan. Mastro runs no model of its own, so it has nothing to resell or mark up.
Can Claude post to a client's books on its own?
Only where your firm says it may. For each area your firm picks does it, asks first, or can't, and what it asks first about waits for a person.
Does the AI see client Social Security or bank account numbers?
Only their last four digits. Employees' pay rates, withholding, home addresses, and tax forms never reach it, and neither do documents, passwords, or access tokens.
Can the same books post differently twice?
No. Rules are deterministic and versioned, and no model runs on the books. A person's Claude acts only when that person asks it to.
How do we see what Claude did?
In the client's activity feed, marked as Claude's, with who it acted for.
Does every client get it?
Only clients with the AI module, which is $29 a client a month. A client without it is out of Claude's reach.