diff --git a/src/cli.rs b/src/cli.rs
index ff0232f..5e86e6f 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -25,7 +25,7 @@ pub struct Cli {
 pub enum SubCommand {
     /// Start reaction daemon
     Start {
-        /// configuration file in json, jsonnet or yaml format. required.
+        /// configuration file in json, jsonnet or yaml format, or directory containing those files. required.
         #[clap(short = 'c', long)]
         config: PathBuf,
 
@@ -90,7 +90,7 @@ Then prints the flushed matches and actions."
 Giving a configuration file permits to use its patterns in REGEX."
     )]
     TestRegex {
-        /// configuration file in json, jsonnet or yaml format. required.
+        /// configuration file in json, jsonnet or yaml format, or directory containing those files. required.
         #[clap(short = 'c', long)]
         config: PathBuf,
 
@@ -102,6 +102,19 @@ Giving a configuration file permits to use its patterns in REGEX."
         #[clap(value_name = "LINE")]
         line: Option<String>,
     },
+    TestConfig {
+        /// configuration file in json, jsonnet or yaml format, or directory containing those files. required.
+        #[clap(short = 'c', long)]
+        config: PathBuf,
+
+        /// how to format output: json or yaml.
+        #[clap(short = 'f', long, default_value_t = Format::YAML)]
+        format: Format,
+
+        /// whether to output additional information
+        #[clap(short = 'v', long, default_value_t = false)]
+        verbose: bool,
+    },
 }
 
 // Enums
diff --git a/src/client/mod.rs b/src/client/mod.rs
index 8565a55..6db6585 100644
--- a/src/client/mod.rs
+++ b/src/client/mod.rs
@@ -1,5 +1,7 @@
 mod show_flush;
+mod test_config;
 mod test_regex;
 
 pub use show_flush::request;
+pub use test_config::test_config;
 pub use test_regex::test_regex;
diff --git a/src/client/test_config.rs b/src/client/test_config.rs
new file mode 100644
index 0000000..3454478
--- /dev/null
+++ b/src/client/test_config.rs
@@ -0,0 +1,42 @@
+use std::{error::Error, path::PathBuf};
+
+use crate::{cli::Format, concepts::Config};
+
+pub fn test_config(
+    config_path: PathBuf,
+    format: Format,
+    verbose: bool,
+) -> Result<(), Box<dyn Error + Send + Sync>> {
+    let (mut cfg, cfg_files) = Config::from_path_raw(&config_path)?;
+    if verbose {
+        if config_path.is_dir() {
+            println!(
+            "Loaded the configuration from the following files in the directory {} in this order:",
+            config_path.display()
+        );
+            println!("{}\n", cfg_files.join("\n"));
+        } else {
+            println!(
+                "Loaded the configuration from the file {}",
+                config_path.display()
+            );
+        }
+    }
+
+    // first serialize the raw config (before regexes are transformed and their original version
+    // discarded)
+    let cfg_str = match format {
+        Format::JSON => serde_json::to_string_pretty(&cfg).map_err(|e| e.to_string()),
+        Format::YAML => serde_yaml::to_string(&cfg).map_err(|e| e.to_string()),
+    }
+    .map_err(|e| format!("Error serializing back the configuration: {e}"))?;
+
+    // then try to finalize the configuration: will raise an error on an invalid config
+    cfg.setup()
+        .map_err(|e| format!("Configuration file {}: {}", config_path.display(), e))?;
+
+    // only print the serialized config if everyting went well
+    println!("{cfg_str}");
+
+    Ok(())
+}
diff --git a/src/concepts/action.rs b/src/concepts/action.rs
index d11462c..51f80e8 100644
--- a/src/concepts/action.rs
+++ b/src/concepts/action.rs
@@ -2,23 +2,28 @@ use std::{cmp::Ordering, collections::BTreeSet, fmt::Display, sync::Arc};
 
 use chrono::TimeDelta;
 
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 use tokio::process::Command;
 
-use super::parse_duration;
+use super::parse_duration::*;
 use super::{Match, Pattern};
 
-#[derive(Clone, Debug, Default, Deserialize)]
+#[derive(Clone, Debug, Default, Deserialize , Serialize)]
 #[serde(deny_unknown_fields)]
 pub struct Action {
     cmd: Vec<String>,
 
     // TODO one shot time deserialization
+    #[serde(skip_serializing_if = "Option::is_none")]
     after: Option<String>,
     #[serde(skip)]
     after_duration: Option<TimeDelta>,
 
-    #[serde(rename = "onexit", default = "set_false")]
+    #[serde(
+        rename = "onexit",
+        default = "set_false",
+        skip_serializing_if = "is_false"
+    )]
     on_exit: bool,
 
     #[serde(skip)]
@@ -35,6 +40,10 @@ fn set_false() -> bool {
     false
 }
 
+fn is_false(b: &bool) -> bool {
+    !*b
+}
+
 impl Action {
     pub fn name(&self) -> &str {
         &self.name
diff --git a/src/concepts/config.rs b/src/concepts/config.rs
index 68e3de8..415dcac 100644
--- a/src/concepts/config.rs
+++ b/src/concepts/config.rs
@@ -7,7 +7,7 @@ use std::{
     sync::Arc,
 };
 
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 use thiserror::Error;
 use tracing::{debug, error, info, warn};
 
@@ -15,7 +15,7 @@ use super::{Filter, Pattern, Stream};
 
 pub type Patterns = BTreeMap<String, Arc<Pattern>>;
 
-#[derive(Clone, Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize, Serialize)]
 #[cfg_attr(test, derive(Default))]
 #[serde(deny_unknown_fields)]
 pub struct Config {
@@ -28,12 +28,12 @@ pub struct Config {
     #[serde(default = "num_cpus::get")]
     concurrency: usize,
 
-    #[serde(default)]
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
     start: Vec<Vec<String>>,
-    #[serde(default)]
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
     stop: Vec<Vec<String>>,
 
-    #[serde(default = "dot")]
+    #[serde(default = "dot", skip_serializing_if = "String::is_empty")]
     state_directory: String,
 
     // This field only serve the purpose of having a top-level place for saving YAML variables
@@ -146,20 +146,22 @@ impl Config {
         run_commands(&self.stop, "stop")
     }
 
-    pub fn from_path(path: &Path) -> Result<(Self, Vec<String>), String> {
+    pub fn from_path_raw(path: &Path) -> Result<(Self, Vec<String>), String> {
         match std::fs::metadata(path) {
             Err(e) => Err(format!("Error accessing {}: {e}", path.to_string_lossy())),
             Ok(m) => {
                 if m.is_file() {
-                    Self::from_file(path).map(|cfg| {
-                        let fname = path
-                            .file_name()
-                            .map(|s| s.to_string_lossy().to_string())
-                            .unwrap_or("".to_string());
-                        (cfg, vec![fname])
-                    })
+                    Self::_from_file_raw(path)
+                        .map(|cfg| {
+                            let fname = path
+                                .file_name()
+                                .map(|s| s.to_string_lossy().to_string())
+                                .unwrap_or("".to_string());
+                            (cfg, vec![fname])
+                        })
+                        .map_err(|e| format!("Configuration file {}: {}", path.display(), e))
                 } else if m.is_dir() {
-                    Self::from_dir(path)
+                    Self::_from_dir_raw(path)
                 } else {
                     Err(format!(
                         "Invalid file type for {}: not a file nor a directory",
@@ -170,7 +172,27 @@ impl Config {
         }
     }
 
-    pub fn from_dir(path: &Path) -> Result<(Self, Vec<String>), String> {
+    pub fn from_path(path: &Path) -> Result<(Self, Vec<String>), String> {
+        match Self::from_path_raw(path) {
+            Ok((mut cfg, files)) => {
+                cfg.setup().map_err(ConfigError::BadConfig).map_err(|e| {
+                    if path.is_dir() {
+                        format!(
+                        "{e}\nWhile reading config from {}. List of files read, in that order:\n{}",
+                        path.display(),
+                        files.join("\n"),
+                    )
+                    } else {
+                        format!("{e}\nWhile reading config from {}.", path.display())
+                    }
+                })?;
+                Ok((cfg, files))
+            }
+            Err(e) => Err(e),
+        }
+    }
+
+    fn _from_dir_raw(path: &Path) -> Result<(Self, Vec<String>), String> {
         let dir = std::fs::read_dir(path)
             .map_err(|e| format!("Error accessing directory {}: {e}", path.display()))?;
         let mut cfg: Option<Self> = None;
@@ -246,14 +268,7 @@ impl Config {
             }
         }
 
-        if let Some(mut cfg) = cfg {
-            cfg.setup().map_err(ConfigError::BadConfig).map_err(|e| {
-                format!(
-                    "{e}\nWhile reading files from {}. List of files read, in that order:\n{}",
-                    path.display(),
-                    read_cfg_fname.join("\n"),
-                )
-            })?;
+        if let Some(cfg) = cfg {
             Ok((cfg, read_cfg_fname))
         } else {
             Err(format!(
@@ -264,8 +279,11 @@ impl Config {
     }
 
     pub fn from_file(path: &Path) -> Result<Self, String> {
-        Config::_from_file(path)
-            .map_err(|err| format!("Configuration file {}: {}", path.display(), err))
+        match Self::_from_file_raw(path) {
+            Ok(mut cfg) => cfg.setup().map(|_| cfg).map_err(ConfigError::BadConfig),
+            Err(e) => Err(e),
+        }
+        .map_err(|err| format!("Configuration file {}: {}", path.display(), err))
     }
 
     fn _extension_to_format(extension: &str) -> Result<Format, ConfigError> {
@@ -289,7 +307,7 @@ impl Config {
         Ok(cfg)
     }
 
-    fn _from_file(path: &Path) -> Result<Self, ConfigError> {
+    fn _from_file_raw(path: &Path) -> Result<Self, ConfigError> {
         let extension = path
             .extension()
             .and_then(|ex| ex.to_str())
@@ -297,11 +315,7 @@ impl Config {
 
         let format = Self::_extension_to_format(extension)?;
 
-        let mut config: Config = Self::_load_file(path, format)?;
-
-        config.setup().map_err(ConfigError::BadConfig)?;
-
-        Ok(config)
+        Self::_load_file(path, format)
     }
 }
 
diff --git a/src/concepts/filter.rs b/src/concepts/filter.rs
index 57d4c67..08b3b5a 100644
--- a/src/concepts/filter.rs
+++ b/src/concepts/filter.rs
@@ -8,7 +8,7 @@ use std::{
 
 use chrono::TimeDelta;
 use regex::Regex;
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 use tracing::info;
 
 use super::parse_duration;
@@ -16,7 +16,7 @@ use super::{Action, Match, Pattern, Patterns};
 
 // Only names are serialized
 // Only computed fields are not deserialized
-#[derive(Clone, Debug, Default, Deserialize)]
+#[derive(Clone, Debug, Default, Deserialize, Serialize)]
 #[serde(deny_unknown_fields)]
 pub struct Filter {
     actions: BTreeMap<String, Action>,
@@ -31,8 +31,9 @@ pub struct Filter {
     #[serde(skip)]
     patterns: Arc<BTreeSet<Arc<Pattern>>>,
 
+    #[serde(skip_serializing_if = "Option::is_none")]
     retry: Option<u32>,
-    #[serde(rename = "retryperiod")]
+    #[serde(rename = "retryperiod", skip_serializing_if = "Option::is_none")]
     retry_period: Option<String>,
     #[serde(skip)]
     retry_duration: Option<TimeDelta>,
@@ -44,6 +45,29 @@ pub struct Filter {
 }
 
 impl Filter {
+    #[cfg(test)]
+    pub fn from_name(stream_name: &str, filter_name: &str) -> Filter {
+        Filter {
+            stream_name: stream_name.into(),
+            name: filter_name.into(),
+            ..Filter::default()
+        }
+    }
+
+    #[cfg(test)]
+    pub fn from_name_and_patterns(
+        stream_name: &str,
+        filter_name: &str,
+        patterns: Vec<Pattern>,
+    ) -> Filter {
+        Filter {
+            stream_name: stream_name.into(),
+            name: filter_name.into(),
+            patterns: Arc::new(patterns.into_iter().map(|p| Arc::new(p)).collect()),
+            ..Filter::default()
+        }
+    }
+
     pub fn name(&self) -> &str {
         &self.name
     }
diff --git a/src/concepts/pattern.rs b/src/concepts/pattern.rs
index 38aae5b..53acbb7 100644
--- a/src/concepts/pattern.rs
+++ b/src/concepts/pattern.rs
@@ -1,18 +1,18 @@
 use std::cmp::Ordering;
 
 use regex::Regex;
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 
-#[derive(Clone, Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize, Serialize)]
 #[cfg_attr(test, derive(Default))]
 #[serde(deny_unknown_fields)]
 pub struct Pattern {
     pub regex: String,
 
-    #[serde(default)]
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
     ignore: Vec<String>,
 
-    #[serde(default, rename = "ignoreregex")]
+    #[serde(default, rename = "ignoreregex", skip_serializing_if = "Vec::is_empty")]
     ignore_regex: Vec<String>,
     #[serde(skip)]
     compiled_ignore_regex: Vec<Regex>,
diff --git a/src/concepts/stream.rs b/src/concepts/stream.rs
index 67e2bfe..907d171 100644
--- a/src/concepts/stream.rs
+++ b/src/concepts/stream.rs
@@ -1,10 +1,10 @@
 use std::{cmp::Ordering, collections::BTreeMap, hash::Hash};
 
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 
 use super::{Filter, Patterns};
 
-#[derive(Clone, Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize, Serialize)]
 #[cfg_attr(test, derive(Default))]
 #[serde(deny_unknown_fields)]
 pub struct Stream {
diff --git a/src/main.rs b/src/main.rs
index 923588a..7379fa9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,7 +3,7 @@ use std::{io::IsTerminal, process::exit};
 use clap::Parser;
 use reaction::{
     cli::{Cli, SubCommand},
-    client::{request, test_regex},
+    client::{request, test_config, test_regex},
     daemon::daemon,
     protocol::Order,
 };
@@ -72,6 +72,11 @@ async fn main() {
             regex,
             line,
         } => test_regex(config, regex, line),
+        SubCommand::TestConfig {
+            config,
+            format,
+            verbose,
+        } => test_config(config, format, verbose),
     };
     match result {
         Ok(()) => {