diff --git a/outlay-core/src/db.rs b/outlay-core/src/db.rs
index 8e88dc2..9282897 100644
--- a/outlay-core/src/db.rs
+++ b/outlay-core/src/db.rs
@@ -469,6 +469,21 @@ impl Database {
         rows.collect()
     }
 
+    pub fn list_all_budgets(&self) -> SqlResult<Vec<Budget>> {
+        let mut stmt = self.conn.prepare(
+            "SELECT id, category_id, amount, month FROM budgets ORDER BY month ASC, id ASC"
+        )?;
+        let rows = stmt.query_map([], |row| {
+            Ok(Budget {
+                id: row.get(0)?,
+                category_id: row.get(1)?,
+                amount: row.get(2)?,
+                month: row.get(3)?,
+            })
+        })?;
+        rows.collect()
+    }
+
     pub fn delete_budget(&self, id: i64) -> SqlResult<()> {
         self.conn.execute("DELETE FROM budgets WHERE id = ?1", params![id])?;
         Ok(())
diff --git a/outlay-core/src/export_json.rs b/outlay-core/src/export_json.rs
index e69de29..1360ba9 100644
--- a/outlay-core/src/export_json.rs
+++ b/outlay-core/src/export_json.rs
@@ -0,0 +1,150 @@
+use crate::db::Database;
+use crate::models::{Budget, Category, RecurringTransaction, Transaction};
+use serde::Serialize;
+use std::io::Write;
+
+#[derive(Debug, Serialize)]
+pub struct ExportData {
+    pub transactions: Vec<Transaction>,
+    pub categories: Vec<Category>,
+    pub budgets: Vec<Budget>,
+    pub recurring: Vec<RecurringTransaction>,
+}
+
+#[derive(Debug)]
+pub enum ExportError {
+    Db(rusqlite::Error),
+    Json(serde_json::Error),
+    Io(std::io::Error),
+}
+
+impl From<rusqlite::Error> for ExportError {
+    fn from(e: rusqlite::Error) -> Self {
+        ExportError::Db(e)
+    }
+}
+
+impl From<serde_json::Error> for ExportError {
+    fn from(e: serde_json::Error) -> Self {
+        ExportError::Json(e)
+    }
+}
+
+impl From<std::io::Error> for ExportError {
+    fn from(e: std::io::Error) -> Self {
+        ExportError::Io(e)
+    }
+}
+
+impl std::fmt::Display for ExportError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ExportError::Db(e) => write!(f, "Database error: {}", e),
+            ExportError::Json(e) => write!(f, "JSON error: {}", e),
+            ExportError::Io(e) => write!(f, "IO error: {}", e),
+        }
+    }
+}
+
+pub fn export_json<W: Write>(db: &Database, writer: W) -> Result<ExportData, ExportError> {
+    let transactions = db.list_all_transactions(None, None)?;
+    let categories = db.list_categories(None)?;
+    let budgets = db.list_all_budgets()?;
+    let recurring = db.list_recurring(false)?;
+
+    let data = ExportData {
+        transactions,
+        categories,
+        budgets,
+        recurring,
+    };
+
+    serde_json::to_writer_pretty(writer, &data)?;
+    Ok(data)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::models::{NewTransaction, TransactionType};
+    use chrono::NaiveDate;
+
+    fn setup_db() -> Database {
+        Database::open_in_memory().unwrap()
+    }
+
+    #[test]
+    fn test_json_export_produces_valid_json() {
+        let db = setup_db();
+        let cats = db.list_categories(Some(TransactionType::Expense)).unwrap();
+
+        let txn = NewTransaction {
+            amount: 25.0,
+            transaction_type: TransactionType::Expense,
+            category_id: cats[0].id,
+            currency: "USD".to_string(),
+            exchange_rate: 1.0,
+            note: Some("Test".to_string()),
+            date: NaiveDate::from_ymd_opt(2026, 3, 1).unwrap(),
+            recurring_id: None,
+        };
+        db.insert_transaction(&txn).unwrap();
+
+        let mut buf = Vec::new();
+        let data = export_json(&db, &mut buf).unwrap();
+
+        assert_eq!(data.transactions.len(), 1);
+        assert!(!data.categories.is_empty());
+        assert!(data.budgets.is_empty());
+        assert!(data.recurring.is_empty());
+
+        // Verify it's valid JSON by parsing it back
+        let output = String::from_utf8(buf).unwrap();
+        let parsed: serde_json::Value = serde_json::from_str(&output).unwrap();
+        assert!(parsed["transactions"].is_array());
+        assert!(parsed["categories"].is_array());
+    }
+
+    #[test]
+    fn test_json_export_includes_all_sections() {
+        let db = setup_db();
+
+        let mut buf = Vec::new();
+        let data = export_json(&db, &mut buf).unwrap();
+
+        // Even with no transactions, we should have default categories
+        assert!(!data.categories.is_empty());
+
+        let output = String::from_utf8(buf).unwrap();
+        assert!(output.contains("\"transactions\""));
+        assert!(output.contains("\"categories\""));
+        assert!(output.contains("\"budgets\""));
+        assert!(output.contains("\"recurring\""));
+    }
+
+    #[test]
+    fn test_json_export_transaction_fields() {
+        let db = setup_db();
+        let cats = db.list_categories(Some(TransactionType::Income)).unwrap();
+
+        let txn = NewTransaction {
+            amount: 500.0,
+            transaction_type: TransactionType::Income,
+            category_id: cats[0].id,
+            currency: "EUR".to_string(),
+            exchange_rate: 0.92,
+            note: Some("Freelance".to_string()),
+            date: NaiveDate::from_ymd_opt(2026, 2, 15).unwrap(),
+            recurring_id: None,
+        };
+        db.insert_transaction(&txn).unwrap();
+
+        let mut buf = Vec::new();
+        export_json(&db, &mut buf).unwrap();
+
+        let output = String::from_utf8(buf).unwrap();
+        assert!(output.contains("500.0"));
+        assert!(output.contains("EUR"));
+        assert!(output.contains("Freelance"));
+    }
+}