diff --git a/src/args/error.rs b/src/args/error.rs
index a56928e..b79a1cc 100644
--- a/src/args/error.rs
+++ b/src/args/error.rs
@@ -17,6 +17,7 @@ pub enum ParseErrorKind
     CannotCombine(char, char),
     BadTail(char, String),
     NotUnique(char),
+    NotUniqueLong(Option<String>),
     ModeSet,
 }
 
@@ -26,7 +27,20 @@ impl fmt::Display for ParseErrorKind
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
     {
-	Ok(())
+	match self {
+	    Self::ExpectedArg(arg) => write!(f, "expected argument {:?}", arg),
+	    Self::UnexpectedArg(None) => write!(f, "unknown argument"),
+	    Self::UnexpectedArg(Some(arg)) => write!(f, "argument {:?} not expected here", arg),
+	    Self::UnknownOption(ch) => write!(f, "unknown option `{}`", ch),
+	    Self::UnknownKeyFormat(key) => write!(f, "unknown key format for {}", key),
+	    Self::UnknownOptionFor(fo, o) => write!(f, "unknown option `{}` for `{}`", o, fo),
+	    Self::CannotCombine(o1,o2) => write!(f, "cannot combine option `{}` with `{}`", o2, o1),
+	    Self::BadTail(ch, ret) => write!(f, "unexpected tail {:?} for option `{}`", ret, ch),
+	    Self::NotUnique(o) => write!(f, "option `{}` already specified", o),
+	    Self::NotUniqueLong(None) => write!(f, "argument already specified"),
+	    Self::NotUniqueLong(Some(opt)) => write!(f, "option {:?} already specified", opt),
+	    Self::ModeSet => write!(f, "mode already set"),
+	}
     }
 }
 
@@ -62,7 +76,10 @@ impl fmt::Display for ConstructError
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
     {
 	match self {
-	    _ => write!(f, "unknown error"),
+	    Self::NoGenerateKind => write!(f, "no key kind specified"),
+	    Self::ExpectedNotPresent(name) => write!(f, "expected a {}, one was not provided", name),
+	    Self::AlreadyExists(opt) => write!(f, "duplicate atom {}", opt),
+	    Self::Resolve(_) => write!(f, "error resolving autodetect"),
 	}
     }
 }
@@ -92,6 +109,9 @@ impl fmt::Display for Error
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
     {
 	match self {
+	    Error::Parse(arg, _) => write!(f, "error while parsing arg {:?}", arg),
+	    Error::ExpectedKind(Some(got)) => write!(f, r#"expected a key kind ("AES" or "RSA"), got {:?}"#, got),
+	    Error::ExpectedKind(None) => write!(f, "expected a key kind"),
 	    Error::AtomInternal => unreachable!("This should've been handled."),
 	    _ => write!(f, "unknown error"),
 	}
diff --git a/src/args/parse/generate.rs b/src/args/parse/generate.rs
index a8139ce..1a4ef89 100644
--- a/src/args/parse/generate.rs
+++ b/src/args/parse/generate.rs
@@ -1,6 +1,7 @@
 //! Parser for generate mode
 use super::*;
 use tokio::sync::mpsc::Receiver;
+use std::collections::HashSet;
 
 #[instrument]
 pub(super) async fn handle(mut rx: Receiver<Atom>) -> Result<config::Operation, error::ConstructError>
@@ -124,8 +125,14 @@ pub(super) async fn parse<I: IntoIterator<Item=String>>(args: I, atoms: &mut mps
 	    }
 	}
 
+	let mut had = HashSet::new();
 	if reading && arg.starts_with("--") {
 	    let (key, value) = split(&arg);
+	    if had.contains(&key[..]) {
+		return Err((error::ParseErrorKind::NotUniqueLong(Some(key.to_owned())), arg).swap().into());
+	    } else {
+		had.insert(key.to_owned());
+	    }
 	    match &key.to_lowercase().trim()[2..] {
 		"input" => send!(GenerateAtom::Input(take_one!("--input: Expected filename"))).await?,
 		"password" if value.is_some() => {
@@ -149,6 +156,12 @@ pub(super) async fn parse<I: IntoIterator<Item=String>>(args: I, atoms: &mut mps
 		_ => return Err((arg, error::ParseErrorKind::UnexpectedArg(None)).into()),
 	    }
 	} else {
+	    
+	    if had.contains(&arg[..]) {
+		return Err((arg, error::ParseErrorKind::NotUniqueLong(None)).into());
+	    } else {
+		had.insert(arg.to_owned());
+	    }
 	    reading=false;
 	    match sent_output
 	    {
@@ -161,6 +174,6 @@ pub(super) async fn parse<I: IntoIterator<Item=String>>(args: I, atoms: &mut mps
 	
     }
     
-    todo!()
+    Ok(())
 }
 
diff --git a/src/resolve.rs b/src/resolve.rs
index c90e3e2..58bfc97 100644
--- a/src/resolve.rs
+++ b/src/resolve.rs
@@ -11,12 +11,14 @@ use std::{
 pub async fn find_file_mode<P: AsRef<Path>>(path: P) -> Result<config::op::Mode, Error>
 {
     //TODO: we need to calculate mode here
+
     todo!()
 }
 
 pub async fn find_key_mode<P: AsRef<Path>>(path: P) -> Result<config::KeyKind, Error>
 {
     //TODO: we need to calculate mode here
+
     todo!()
 }
 
@@ -24,7 +26,7 @@ pub async fn find_key_mode<P: AsRef<Path>>(path: P) -> Result<config::KeyKind, E
 #[non_exhaustive]
 pub enum Error
 {
-    
+    Unknown
 }
 
 impl error::Error for Error{}
@@ -32,6 +34,8 @@ impl fmt::Display for Error
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
     {
-	Ok(())
+	match self {
+	    _ => write!(f, "unknown error"),
+	}
     }
 }