diff --git a/Cargo.toml b/Cargo.toml
index 6c6e246..c929043 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,7 +24,7 @@ tokio = { version = "1.41", features = ["full"] }
 #tracing-subscriber = "0.3"
 
 [dev-dependencies]
-#assert2 = "0.3"
+assert2 = "0.3"
 mutants = "0.0"
 #pretty_assertions = "1.4"
-#test-log = { version = "0.2", features = ["trace"] }
+test-log = { version = "0.2", features = ["trace"] }
diff --git a/src/default-config.toml b/src/default-config.toml
new file mode 100644
index 0000000..3b73a8f
--- /dev/null
+++ b/src/default-config.toml
@@ -0,0 +1,11 @@
+[trello]
+api_key = ""
+api_secret = ""
+user = ""
+board_name = ""
+
+[nextcloud]
+username = ""
+password = ""
+hostname = ""
+board_id = 1
diff --git a/src/init.rs b/src/init.rs
new file mode 100644
index 0000000..418cb0e
--- /dev/null
+++ b/src/init.rs
@@ -0,0 +1,25 @@
+//
+use std::collections::HashMap;
+
+use color_eyre::eyre::{eyre, Result};
+
+use crate::{f, p, s, template, Ctx, NAME};
+
+pub(crate) fn run(ctx: &Ctx) -> Result<()> {
+    let path = ctx.fs.base().join(f!("{NAME}.toml"));
+    let file = ctx.fs.file(&path);
+
+    if file.exists()? {
+        Err(eyre!("File already exists - not overwriting: {file}"))
+    } else {
+        file.write(include_str!("default-config.toml"))?;
+        p!(
+            "{}",
+            template::expand(
+                include_str!("post-init-instructions.txt"),
+                HashMap::from([("NAME", NAME), ("file", s!(file).as_str())])
+            )
+        );
+        Ok(())
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 6ed90a4..b06130f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,7 +4,12 @@ use std::path::PathBuf;
 use clap::Parser;
 use kxio::{fs::FileSystem, net::Net};
 
+mod init;
 mod macros;
+mod template;
+
+#[cfg(test)]
+mod tests;
 
 pub const NAME: &str = "trello-to-deck";
 
@@ -36,14 +41,15 @@ impl Default for Ctx {
 }
 
 #[cfg_attr(test, mutants::skip)]
-pub async fn run(_ctx: Ctx) -> color_eyre::Result<()> {
+pub async fn run(ctx: Ctx) -> color_eyre::Result<()> {
     color_eyre::install()?;
 
     let commands = Commands::parse();
     match commands.command {
-        Command::Init => todo!("init"),
+        Command::Init => init::run(&ctx)?,
         Command::Check => todo!("check"),
         Command::Import => todo!("import"),
     };
-    // Ok(())
+
+    Ok(())
 }
diff --git a/src/post-init-instructions.txt b/src/post-init-instructions.txt
new file mode 100644
index 0000000..41c3676
--- /dev/null
+++ b/src/post-init-instructions.txt
@@ -0,0 +1,10 @@
+The default configuration has been written to {file}.
+
+Next:
+
+- Edit the file to;
+  - add credentials for Trello and NextCloud
+  - add details of the Trello Board and Lists that should be imported
+  - add details of the NextCloud Deck to import to
+- Verify the file: {NAME} check
+- When happy: {NAME} import
diff --git a/src/template.rs b/src/template.rs
new file mode 100644
index 0000000..48ecc1a
--- /dev/null
+++ b/src/template.rs
@@ -0,0 +1,10 @@
+//
+use std::collections::HashMap;
+
+pub(crate) fn expand(template: &str, params: HashMap<&str, &str>) -> String {
+    let mut result = template.to_string();
+    for (key, value) in params {
+        result = result.replace(&format!("{{{key}}}"), value);
+    }
+    result
+}
diff --git a/src/tests/mod.rs b/src/tests/mod.rs
new file mode 100644
index 0000000..f1a8183
--- /dev/null
+++ b/src/tests/mod.rs
@@ -0,0 +1,90 @@
+//
+
+// type TestResult = Result<(), Box<dyn std::error::Error>>;
+
+use assert2::let_assert;
+
+mod init {
+
+    use test_log::test;
+
+    use crate::{f, init::run, NAME};
+
+    use super::given;
+    use super::*;
+
+    #[test]
+    fn when_file_does_not_exist_should_create() {
+        //given
+        let fs = given::a_filesystem();
+        let ctx = given::a_context(fs.as_real(), given::a_network().into());
+
+        //when
+        let_assert!(Ok(_) = run(&ctx));
+
+        //then
+        let path = ctx.fs.base().join(f!("{NAME}.toml"));
+        let file = ctx.fs.file(&path);
+        let contents = file.reader().expect("read file").to_string();
+        assert_eq!(contents, include_str!("../default-config.toml"));
+    }
+
+    #[test]
+    fn when_file_exists_should_err() {
+        //given
+        let fs = given::a_filesystem();
+        let path = fs.base().join(f!("{NAME}.toml"));
+        let file = fs.file(&path);
+        file.write("").expect("create file");
+
+        let ctx = given::a_context(fs.as_real(), given::a_network().into());
+        //when
+        let_assert!(Err(err) = run(&ctx));
+
+        //then
+        assert!(err
+            .to_string()
+            .contains("File already exists - not overwriting"));
+    }
+}
+
+mod template {
+
+    use std::collections::HashMap;
+
+    use crate::template;
+
+    #[test]
+    fn expand_should_substitute_values() {
+        //given
+        let template = "pre{param1}mid{param2}post";
+        let params = HashMap::from([("param1", "-v1-"), ("param2", "-v2-")]);
+
+        //when
+        let result = template::expand(template, params);
+
+        //then
+        assert_eq!(result, "pre-v1-mid-v2-post");
+    }
+}
+
+mod given {
+    use kxio::{
+        fs::{FileSystem, TempFileSystem},
+        net::{MockNet, Net},
+    };
+
+    use crate::Ctx;
+
+    pub fn a_context(fs: FileSystem, net: Net) -> Ctx {
+        Ctx { fs, net }
+    }
+
+    pub fn a_filesystem() -> TempFileSystem {
+        kxio::fs::temp().expect("temp fs")
+    }
+
+    pub fn a_network() -> MockNet {
+        kxio::net::mock()
+    }
+}