diff --git a/packages/devkit/README.md b/packages/devkit/README.md
index ea08c49..6d90a2b 100644
--- a/packages/devkit/README.md
+++ b/packages/devkit/README.md
@@ -214,6 +214,102 @@ devkit mock --port 8080 --scenario spike
 stellar-devkit = { path = "../devkit" }
 ```
 
+## Sandbox
+
+The `sandbox` module provides a scenario-driven testing DSL for simulating Stellar fee environments in isolation. It lets you compose network conditions, inject fixtures, and run assertions against simulated fee streams.
+
+### Scenarios
+
+Use `Scenario::builder()` to construct reproducible fee scenarios via a builder DSL:
+
+```rust
+use stellar_devkit::sandbox::Scenario;
+
+let scenario = Scenario::builder("my_test")
+    .with_base_fee(200)
+    .with_spike_probability(0.15)
+    .with_ledger_count(500)
+    .with_seed(42)
+    .build();
+```
+
+Each builder method configures a dimension of the simulation. The builder enforces valid ranges and returns errors for out-of-bound values. Once built, a `Scenario` is immutable and can be reused across multiple simulation runs.
+
+### Fixtures
+
+Pre-built fixture profiles capture common network states:
+
+| Fixture | Description |
+|---|---|
+| `Normal` | Low-fee baseline with minimal spikes; ideal for regression testing |
+| `Congested` | Sustained high-fee demand with elevated base fees |
+| `HighVariance` | Wide fee swings and frequent spikes; tests volatility handling |
+| `Recovery` | Starts congested and gradually returns to baseline; tests cooldown logic |
+| `Spike` | Mostly calm with a single sharp fee spike; tests spike detection |
+
+Load a fixture by name:
+
+```rust
+use stellar_devkit::sandbox::fixtures::{Fixture, load_fixture};
+
+let fixture = load_fixture(Fixture::Congested);
+let scenario = fixture.into_scenario();
+```
+
+### Runner
+
+The `Runner` executes a sandbox closure against a scenario, managing the simulation lifecycle:
+
+```rust
+use stellar_devkit::sandbox::{Scenario, Runner};
+
+let scenario = Scenario::builder("example")
+    .with_ledger_count(100)
+    .build();
+
+Runner::new(scenario).run(|ctx| {
+    // ctx provides access to generated fees, timestamps, and metadata
+    assert!(!ctx.fees().is_empty());
+    println!("Simulated {} ledgers", ctx.fees().len());
+});
+```
+
+The runner handles RNG seeding, timestamp generation, and fee model execution internally. The closure receives a `SandboxContext` with read access to all simulation outputs.
+
+### Assertion helpers
+
+The sandbox provides built-in assertion helpers for common test validations:
+
+```rust
+use stellar_devkit::sandbox::assertions::*;
+
+// Assert all fees fall within an expected range
+assert_fee_in_range(&fees, min_stroops, max_stroops);
+
+// Assert the number of spikes matches expectations
+assert_spike_count(&fees, expected_count);
+
+// Assert the quality score exceeds a threshold (0.0–1.0)
+assert_quality_score_above(&fees, 0.8);
+```
+
+### Time travel
+
+Control simulated time to test time-dependent logic:
+
+```rust
+use stellar_devkit::sandbox::time::*;
+
+// Advance the simulation clock by a duration
+advance_time(Duration::from_secs(3600));
+
+// Set the clock to an absolute timestamp
+set_time(1_700_000_000);
+
+// Read the current simulated time
+let now = current_time();
+```
+
 ## Benchmarks
 
 Baseline results measured on reference hardware (Apple M-series, single-core, `cargo bench`):
diff --git a/packages/devkit/tests/common/mod.rs b/packages/devkit/tests/common/mod.rs
new file mode 100644
index 0000000..9199ad4
--- /dev/null
+++ b/packages/devkit/tests/common/mod.rs
@@ -0,0 +1,5 @@
+pub mod setup;
+pub mod teardown;
+
+pub use setup::*;
+pub use teardown::*;
diff --git a/packages/devkit/tests/common/setup.rs b/packages/devkit/tests/common/setup.rs
new file mode 100644
index 0000000..801bc7f
--- /dev/null
+++ b/packages/devkit/tests/common/setup.rs
@@ -0,0 +1,58 @@
+use std::path::{Path, PathBuf};
+use tempfile::TempDir;
+
+pub struct TestContext {
+    pub temp_dir: TempDir,
+    pub fixtures_dir: PathBuf,
+}
+
+impl TestContext {
+    pub fn new() -> Self {
+        let temp_dir = tempfile::tempdir().expect("Failed to create temp dir");
+        let fixtures_dir = temp_dir.path().join("fixtures");
+        std::fs::create_dir_all(&fixtures_dir).expect("Failed to create fixtures dir");
+
+        Self {
+            temp_dir,
+            fixtures_dir,
+        }
+    }
+
+    pub fn fixture_path(&self, name: &str) -> PathBuf {
+        self.fixtures_dir.join(name)
+    }
+
+    pub fn write_fixture(&self, name: &str, content: &str) -> PathBuf {
+        let path = self.fixture_path(name);
+        std::fs::write(&path, content).expect("Failed to write fixture");
+        path
+    }
+}
+
+pub struct TestDatabase {
+    path: PathBuf,
+}
+
+impl TestDatabase {
+    pub fn new() -> Self {
+        let path = std::env::temp_dir().join(format!("test_{}.db", uuid::Uuid::new_v4()));
+        Self { path }
+    }
+
+    pub fn path(&self) -> &Path {
+        &self.path
+    }
+
+    pub fn connection_string(&self) -> String {
+        format!("sqlite:{}", self.path.display())
+    }
+}
+
+impl Drop for TestDatabase {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_file(&self.path);
+        let _ = std::fs::remove_file(format!("{}-journal", self.path.display()));
+        let _ = std::fs::remove_file(format!("{}-wal", self.path.display()));
+        let _ = std::fs::remove_file(format!("{}-shm", self.path.display()));
+    }
+}
diff --git a/packages/devkit/tests/common/teardown.rs b/packages/devkit/tests/common/teardown.rs
new file mode 100644
index 0000000..04a4985
--- /dev/null
+++ b/packages/devkit/tests/common/teardown.rs
@@ -0,0 +1,20 @@
+use std::path::Path;
+
+pub fn cleanup_test_artifacts(dir: &Path) {
+    if dir.exists() {
+        let _ = std::fs::remove_dir_all(dir);
+    }
+}
+
+pub fn assert_no_temp_files_remaining(dir: &Path) {
+    if dir.exists() {
+        let entries: Vec<_> = std::fs::read_dir(dir)
+            .map(|e| e.filter_map(|e| e.ok()).collect())
+            .unwrap_or_default();
+        assert!(
+            entries.is_empty(),
+            "Temp directory should be clean but has {} entries",
+            entries.len()
+        );
+    }
+}
diff --git a/packages/devkit/tests/integration_csv_writer.rs b/packages/devkit/tests/integration_csv_writer.rs
new file mode 100644
index 0000000..8278cbb
--- /dev/null
+++ b/packages/devkit/tests/integration_csv_writer.rs
@@ -0,0 +1,49 @@
+use std::io::Write;
+use tempfile::NamedTempFile;
+
+use stellar_devkit::io::csv::CsvWriter;
+
+#[test]
+fn test_csv_writer_creates_valid_file() {
+    let mut csv_file = NamedTempFile::new().expect("Failed to create temp file");
+    {
+        let mut writer = CsvWriter::new(&mut csv_file).expect("Failed to create CsvWriter");
+        writer.write_header().expect("Failed to write header");
+        for i in 0..10 {
+            writer
+                .write_row(stellar_devkit::io::csv::FeeRecord {
+                    timestamp_ms: 1700000000000 + i * 6000,
+                    fee_stroops: 100 + i as u64,
+                    sequence: i as u64,
+                })
+                .expect("Failed to write row");
+        }
+        writer.flush().expect("Failed to flush");
+    }
+
+    let content = std::fs::read_to_string(csv_file.path()).expect("Failed to read file");
+    let lines: Vec<&str> = content.lines().collect();
+    assert_eq!(lines.len(), 11, "expected 1 header + 10 data rows");
+    assert!(lines[0].contains("timestamp_ms"), "header should contain timestamp_ms");
+}
+
+#[test]
+fn test_csv_writer_roundtrip() {
+    let mut csv_file = NamedTempFile::new().expect("Failed to create temp file");
+    let record = stellar_devkit::io::csv::FeeRecord {
+        timestamp_ms: 1700000000000,
+        fee_stroops: 3849,
+        sequence: 42,
+    };
+    {
+        let mut writer = CsvWriter::new(&mut csv_file).expect("Failed to create CsvWriter");
+        writer.write_header().expect("Failed to write header");
+        writer.write_row(record).expect("Failed to write row");
+        writer.flush().expect("Failed to flush");
+    }
+
+    let content = std::fs::read_to_string(csv_file.path()).expect("Failed to read file");
+    assert!(content.contains("1700000000000"), "should contain timestamp");
+    assert!(content.contains("3849"), "should contain fee_stroops");
+    assert!(content.contains("42"), "should contain sequence");
+}
diff --git a/packages/devkit/tests/integration_db_factory.rs b/packages/devkit/tests/integration_db_factory.rs
new file mode 100644
index 0000000..34b829a
--- /dev/null
+++ b/packages/devkit/tests/integration_db_factory.rs
@@ -0,0 +1,37 @@
+use std::sync::Arc;
+use std::path::PathBuf;
+
+#[test]
+fn test_db_factory_creates_sqlite_database() {
+    let temp_dir = tempfile::tempdir().expect("Failed to create temp dir");
+    let db_path = temp_dir.path().join("test_factory.db");
+
+    let conn_str = format!("sqlite:{}", db_path.display());
+
+    assert!(conn_str.starts_with("sqlite:"), "connection string should start with sqlite:");
+    assert!(
+        conn_str.contains("test_factory.db"),
+        "connection string should contain database name"
+    );
+}
+
+#[test]
+fn test_db_factory_in_memory_database() {
+    let conn_str = "sqlite::memory:";
+
+    assert!(
+        conn_str.contains("memory"),
+        "in-memory connection should contain 'memory'"
+    );
+}
+
+#[test]
+fn test_db_factory_multiple_connections() {
+    let temp_dir = tempfile::tempdir().expect("Failed to create temp dir");
+    let db_path = temp_dir.path().join("multi_conn.db");
+
+    let conn_str1 = format!("sqlite:{}", db_path.display());
+    let conn_str2 = format!("sqlite:{}", db_path.display());
+
+    assert_eq!(conn_str1, conn_str2, "same path should produce same connection string");
+}