diff --git a/rust/src/args.rs b/rust/src/args.rs
index 040fb14..8b00be2 100644
--- a/rust/src/args.rs
+++ b/rust/src/args.rs
@@ -1,10 +1,11 @@
 use clap::{Args, Parser, Subcommand};
+use thiserror::Error;
 use tracing::Level;
 
 #[derive(Debug, Parser)]
 #[clap(version, about)]
 pub struct CommandArgs {
-    /// The path to the TOML configuration. This will override all other configuration sources
+    /// The path to a TOML or JSON configuration to use. This will me merged with all other configuration sources, taking priority over other files but not environment variables
     #[arg(short, long)]
     pub config: Option<String>,
 
@@ -24,3 +25,9 @@ pub struct ServeAction {
     #[arg(short, long, default_value_t = Level::WARN)]
     pub log_level: Level,
 }
+
+#[derive(Error, Debug)]
+pub enum ArgsError {
+    #[error("the file extension of the provided config file is not one of .json or .toml")]
+    InvalidConfigExtension(Option<String>),
+}
diff --git a/rust/src/error.rs b/rust/src/error.rs
index 611ce1d..c622051 100644
--- a/rust/src/error.rs
+++ b/rust/src/error.rs
@@ -1,10 +1,15 @@
 use thiserror::Error;
 
+use crate::args;
+
 #[derive(Error, Debug)]
 pub enum CommandError {
     #[error("the configuration is invalid")]
     InvalidConfig(#[from] Box<figment::Error>),
 
+    #[error("a commandline argument is invalid")]
+    InvalidArgument(#[from] args::ArgsError),
+
     #[error(transparent)]
     Unknown(#[from] anyhow::Error),
     // examples
diff --git a/rust/src/main.rs b/rust/src/main.rs
index 1f7e9ec..b5cc898 100644
--- a/rust/src/main.rs
+++ b/rust/src/main.rs
@@ -1,3 +1,5 @@
+use std::path::Path;
+
 use clap::Parser;
 use figment::{
     Figment,
@@ -6,22 +8,37 @@ use figment::{
 use tracing::{Level, event};
 
 mod args;
-use args::{ActionType, CommandArgs};
+use crate::args::{ActionType, ArgsError, CommandArgs};
 
 mod config;
 
 mod error;
-use error::CommandError;
+use crate::error::CommandError;
 
 #[tokio::main]
 async fn main() -> Result<(), CommandError> {
     let args = CommandArgs::parse();
 
-    let config: config::CommandConfig = Figment::new()
+    let figment = Figment::new()
         .admerge(Json::file("config.json"))
-        .admerge(Toml::file("config.toml"))
-        .admerge(Env::prefixed("APP_"))
-        .extract()?;
+        .admerge(Toml::file("config.toml"));
+
+    let config: config::CommandConfig = match &args.config {
+        None => figment,
+        Some(f) => {
+            let file = Path::new(&f);
+
+            match file.extension().and_then(|e| e.to_str()) {
+                Some("toml") => Ok(figment.admerge(Toml::file(file))),
+                Some("json") => Ok(figment.admerge(Json::file(file))),
+                _ => Err(ArgsError::InvalidConfigExtension(
+                    file.extension().and_then(|e| e.to_str().map(String::from)),
+                )),
+            }
+        }?,
+    }
+    .admerge(Env::prefixed("APP_"))
+    .extract()?;
 
     match &args.action {
         ActionType::Serve(serve_args) => {
@@ -41,7 +58,9 @@ async fn main() -> Result<(), CommandError> {
 
             println!("{:#?}", config.port.ports);
         }
-    }
+    };
+
+    println!("{}", CommandError::InvalidArgument(ArgsError::InvalidConfigExtension(Some(String::from("txt")))));
 
     Ok(())
 }