Building Slack alerts with Claude

The limitation to set before we start

Let's be direct about this, since it's the question we get most often: the Spendesk MCP has no webhooks or push notifications. There's no mechanism that lets Spendesk warn Claude in real time that something happened (an invoice received, a threshold crossed, an approval pending).

What this guide calls a "Slack alert" is therefore never a true real-time push — it's always the combination of two things you've already seen:

1. A routine that pulls data from the MCP on a schedule.
2. Claude's Slack connector, which pushes that routine's result into a channel.

That's an important distinction: the alert has the frequency of the routine, not the instantaneity of a real push.

Three real client needs, and how to cover them

Budget overrun alerts (a need raised by several CFOs) — caveat: the Spendesk MCP doesn't expose a get_budgets tool. So there's no strict "budget vs actual" check available. What is possible is an approximation via spendesk_analyze_spend, comparing spend in one period against a reference period — useful to spot drift, but not a formal budget control.

Filtered approval alerts (a Procurement need) — via get_requests, a routine can watch for requests pending approval for more than N days and flag the ones past a threshold.

Missing invoice alerts (a CFO/AP need) — by cross-referencing get_purchase_orders and get_payables, or via spendesk_get_due_invoices, a routine can flag invoices that haven't arrived when they were expected.

What a Slack alert looks like in practice

The prompt to copy to get started

Every [frequency — e.g. Monday at 9am], send a summary of [business need — e.g. invoices overdue by more than 15 days] to the Slack channel [#channel-name], based on [MCP tool — e.g. spendesk_get_due_invoices]. Include the total amount and the 3 most critical cases.

For CFOs: start with a weekly digest rather than a daily one — a Slack channel that gets a message every day is quickly ignored, while a well-built weekly summary stays read.

For Procurement: always filter by cost center or minimum amount — an unfiltered alert on every purchase request quickly becomes noise.

What to keep in mind before rolling this out to your team

• The alert has the frequency of the routine that triggers it, never the instantaneity of a true push.
• "Budget vs actual" remains an approximation as long as get_budgets doesn't exist in the MCP — present it as a trend indicator, not a formal control.
• Test the routine in a manual conversation first before wiring it to a shared channel — a badly calibrated alert sent to a whole team is harder to walk back afterward.

To go further and learn to assess yourself what the MCP can and can't do for a given need: Using Claude as a thinking partner.