diff --git a/crates/ledger-mcp/src/policy.rs b/crates/ledger-mcp/src/policy.rs
new file mode 100644
index 0000000..bd5c4e0
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+++ b/crates/ledger-mcp/src/policy.rs
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+//! The receipt policy: server-side enforcement, not prose.
+//!
+//! Posting an entry whose debits are strictly greater than the configured
+//! threshold requires at least one attached receipt, unless every line is in
+//! an exempt account. Selected accounts can require receipts regardless of
+//! amount. Reversals are exempt: the original entry carries the evidence.
+
+use ledger_core::{JournalEntry, Ledger, Side};
+use rust_decimal::Decimal;
+use serde::Deserialize;
+
+/// Server-side receipt policy, loaded from config.
+#[derive(Debug, Clone, Deserialize)]
+pub struct ReceiptPolicy {
+    /// Receipts required when an entry's debits are strictly greater than
+    /// this amount. Decimal string, e.g. `"25.00"`.
+    #[serde(default = "default_threshold")]
+    pub require_receipts_above: String,
+    /// Account codes that always require a receipt, regardless of amount.
+    #[serde(default)]
+    pub receipt_required_accounts: Vec<String>,
+    /// Account codes exempt from the policy. The exemption applies only when
+    /// *every* line of the entry is in an exempt account.
+    #[serde(default)]
+    pub receipt_exempt_accounts: Vec<String>,
+}
+
+fn default_threshold() -> String {
+    "25.00".to_string()
+}
+
+impl Default for ReceiptPolicy {
+    fn default() -> Self {
+        Self {
+            require_receipts_above: default_threshold(),
+            receipt_required_accounts: Vec::new(),
+            receipt_exempt_accounts: Vec::new(),
+        }
+    }
+}
+
+impl ReceiptPolicy {
+    fn threshold(&self) -> Decimal {
+        self.require_receipts_above
+            .parse()
+            .unwrap_or(Decimal::from(25))
+    }
+
+    fn account_codes(&self, ledger: &Ledger, entry: &JournalEntry) -> Vec<String> {
+        entry
+            .lines()
+            .iter()
+            .map(|l| {
+                ledger
+                    .chart()
+                    .get(l.account)
+                    .map(|a| a.code.clone())
+                    .unwrap_or_default()
+            })
+            .collect()
+    }
+
+    /// Total debits of the entry (one side of the balanced entry).
+    pub fn entry_debits(entry: &JournalEntry) -> Decimal {
+        entry
+            .lines()
+            .iter()
+            .filter(|l| l.side == Side::Debit)
+            .map(|l| l.amount.amount)
+            .sum()
+    }
+
+    /// True when posting this entry requires at least one receipt.
+    pub fn receipt_required(&self, ledger: &Ledger, entry: &JournalEntry) -> bool {
+        let codes = self.account_codes(ledger, entry);
+        // Per-account override: any line in a required account → required.
+        if codes
+            .iter()
+            .any(|c| self.receipt_required_accounts.iter().any(|r| r == c))
+        {
+            return true;
+        }
+        // Strictly greater than the threshold (Stephen: ">$25").
+        if Self::entry_debits(entry) <= self.threshold() {
+            return false;
+        }
+        // Exempt only when every line is in an exempt account.
+        !codes
+            .iter()
+            .all(|c| self.receipt_exempt_accounts.iter().any(|e| e == c))
+    }
+
+    /// Human-readable policy summary for previews and errors.
+    pub fn describe(&self) -> String {
+        format!(
+            "receipts required when entry debits are strictly greater than {}",
+            self.threshold()
+        )
+    }
+}