diff --git a/app/src/alert_swiss.rs b/app/src/alert_swiss.rs
index 058a55c..6469a8c 100644
--- a/app/src/alert_swiss.rs
+++ b/app/src/alert_swiss.rs
@@ -1,7 +1,9 @@
 use crate::json::alerts::Alerts;
 
+// TODO: maybe make this overridable?
 const ALERT_SWISS_URL: &str = "https://www.alert.swiss/content/alertswiss-internet/en/home/_jcr_content/polyalert.alertswiss_alerts.actual.json";
 
+/// Fetch alert information from alertswiss as a json document.
 pub async fn fetch_alerts() -> Result<Alerts, reqwest::Error> {
     reqwest::get(ALERT_SWISS_URL).await?.json::<Alerts>().await
 }
diff --git a/app/src/cli.rs b/app/src/cli.rs
index 0d898c0..c6badc8 100644
--- a/app/src/cli.rs
+++ b/app/src/cli.rs
@@ -9,6 +9,7 @@ pub struct Cli {
     /// Update interval in seconds
     #[arg(short, long, default_value_t = 10)]
     pub interval: u64,
+
     /// Database connection string where timestamps are stored (SQLite, Postgres or MySql)
     #[arg(short, long, default_value_t = format!("sqlite::memory:"))]
     pub connection: String,
diff --git a/app/src/datastore/rdbms.rs b/app/src/datastore/rdbms.rs
index 09ace30..ced9f0f 100644
--- a/app/src/datastore/rdbms.rs
+++ b/app/src/datastore/rdbms.rs
@@ -1,3 +1,6 @@
+//! Provide functionality to interact with a relational database
+//! for storing and retrieving alert information.
+
 use entity::alerts;
 use migration::{Migrator, MigratorTrait};
 use sea_orm::{ActiveModelTrait, DatabaseConnection, EntityTrait, Set};
@@ -14,11 +17,13 @@ pub enum RdbmsError {
     DbError(#[from] sea_orm::DbErr),
 }
 
+/// Wrap a database connection and allow operations on it.
 pub struct Db {
     connection: DatabaseConnection,
 }
 
 impl Db {
+    /// Check if an alert has been updated in the database.
     pub async fn is_alert_updated(&self, alert: &Alert) -> Result<bool, RdbmsError> {
         let db_alert = entity::alerts::Entity::find_by_id(&alert.identifier)
             .one(&self.connection)
@@ -30,6 +35,7 @@ impl Db {
         })
     }
 
+    /// Save an alert to the database.
     pub async fn save_alert(&self, alert: &Alert) -> Result<(), RdbmsError> {
         let db_alert = entity::alerts::Entity::find_by_id(&alert.identifier)
             .one(&self.connection)
@@ -49,6 +55,9 @@ impl Db {
     }
 }
 
+/// Establish a connection to a database.
+///
+/// Run all migrations.
 pub async fn connect(connection_string: &str) -> Result<Db, RdbmsError> {
     debug!("connecting to {connection_string}...");
 
diff --git a/app/src/lib.rs b/app/src/lib.rs
index 46c997f..cc769e1 100644
--- a/app/src/lib.rs
+++ b/app/src/lib.rs
@@ -48,6 +48,9 @@ mod json {
 pub mod logging;
 pub mod mqtt;
 
+/// Check for new alerts, save them into the local database and publish them to mqtt.
+///
+/// Return new alerts.
 async fn handle_alerts(db: &Db) -> Result<Vec<Alert>, Error> {
     info!("checking alerts");
 
@@ -56,8 +59,10 @@ async fn handle_alerts(db: &Db) -> Result<Vec<Alert>, Error> {
         .list
         .into_iter()
         .filter(|alert| !alert.identifier.starts_with("TEST-"))
+        // we do not need the test alerts
         .collect();
 
+    // filter for new alerts by checking with the database
     let new_alerts: Vec<Alert> = stream::iter(alerts)
         .filter_map(|alert| async move {
             if db.is_alert_updated(&alert).await.ok().unwrap_or(false) {
@@ -69,6 +74,7 @@ async fn handle_alerts(db: &Db) -> Result<Vec<Alert>, Error> {
         .collect()
         .await;
 
+    // persist new alerts
     stream::iter(new_alerts.clone())
         .for_each_concurrent(None, |alert| async move {
             info!("saving alert {}", alert.identifier);
@@ -81,6 +87,7 @@ async fn handle_alerts(db: &Db) -> Result<Vec<Alert>, Error> {
     Ok(new_alerts)
 }
 
+/// Entry point to run the alert-me application.
 pub async fn run(config: Config) -> Result<(), Error> {
     let mut interval = time::interval(Duration::from_secs(config.interval));
 
diff --git a/app/src/mqtt.rs b/app/src/mqtt.rs
index 657cf75..45e8640 100644
--- a/app/src/mqtt.rs
+++ b/app/src/mqtt.rs
@@ -1,3 +1,5 @@
+//! MQTT publishing.
+
 use rumqttc::{AsyncClient, EventLoop, MqttOptions, QoS};
 use std::{sync::Arc, time::Duration};
 use tokio::sync::Mutex;
@@ -5,6 +7,7 @@ use tracing::debug;
 
 use crate::{config::MqttConfig, error::Error};
 
+/// Encapsulate the MQTT eventloop for publishing data.
 pub struct Mqtt {
     client: AsyncClient,
     eventloop: Arc<Mutex<EventLoop>>,
@@ -12,6 +15,7 @@ pub struct Mqtt {
 }
 
 impl Mqtt {
+    /// Run the MQTT event loop to properly receive messages.
     async fn run_event_loop(&self) {
         let mut event_loop_running = self.event_loop_running.lock().await;
         if !*event_loop_running {
@@ -28,6 +32,7 @@ impl Mqtt {
         }
     }
 
+    /// Publish data to an MQTT topic with QoS `AtLeastOnce`..
     pub async fn publish(&self, payload: &[u8]) -> Result<(), Error> {
         self.run_event_loop().await;
         self.client
@@ -38,6 +43,7 @@ impl Mqtt {
     }
 }
 
+/// Connect and authenticate to an MQTT broker.
 pub fn connect(config: &MqttConfig) -> Mqtt {
     let mut options = MqttOptions::new("rumqtt-async", config.broker.clone(), config.port);
     let options = options