diff --git a/src/args.rs b/src/args.rs
index cd37b79..b1b93a6 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -143,7 +143,7 @@ pub struct OptionsArgs {
 }
 
 /// Enum for representing either a number (item ID) or a string (tag).
-#[derive(Debug, Clone, From)]
+#[derive(Debug, Clone)]
 pub enum NumberOrString {
     Number(i64),
     Str(String),
diff --git a/src/modes/common.rs b/src/modes/common.rs
index 7cc9611..abab8c8 100644
--- a/src/modes/common.rs
+++ b/src/modes/common.rs
@@ -440,5 +440,3 @@ pub fn create_table_with_config(table_config: &crate::config::TableConfig) -> Ta
     table
 }
 
-/// Exports public types and functions for use in other modules.
-pub use self::{ColumnType, OutputFormat, format_size, settings_output_format};
diff --git a/src/modes/diff.rs b/src/modes/diff.rs
index 6cf2778..522a24b 100644
--- a/src/modes/diff.rs
+++ b/src/modes/diff.rs
@@ -10,48 +10,7 @@ use crate::config;
 use crate::services::item_service::ItemService;
 use log::debug;
 
-/// Validates diff arguments and exits with error if invalid.
-///
-/// This function checks that exactly two item IDs are provided and no tags are used
-/// with the diff mode, exiting with an appropriate error message if validation fails.
-///
-/// # Arguments
-///
-/// * `cmd` - Command instance for error reporting.
-/// * `ids` - Vector of item IDs.
-/// * `tags` - Vector of tags (should be empty for diff mode).
-fn validate_diff_args(cmd: &mut Command, ids: &Vec<i64>, tags: &Vec<String>) {
-    if !tags.is_empty() {
-        cmd.error(
-            clap::error::ErrorKind::InvalidValue,
-            "Tags are not supported with --diff. Please provide exactly two IDs.",
-        )
-        .exit();
-    }
-    if ids.len() != 2 {
-        cmd.error(
-            clap::error::ErrorKind::InvalidValue,
-            "You must supply exactly two IDs when using --diff.",
-        )
-        .exit();
-    }
-}
-
-/// Validates the diff arguments and returns a Result if valid.
-///
-/// This function performs the same validation as `validate_diff_args` but returns
-/// an error instead of exiting, allowing for programmatic handling.
-///
-/// # Arguments
-///
-/// * `cmd` - Command instance for error reporting.
-/// * `ids` - Vector of item IDs to fetch.
-/// * `tags` - Vector of tags (should be empty for diff mode).
-///
-/// # Returns
-///
-/// * `anyhow::Result<()>` - Ok if valid, Err with error message if invalid.
-fn validate_diff_args(cmd: &mut Command, ids: &Vec<i64>, tags: &Vec<String>) -> anyhow::Result<()> {
+fn validate_diff_args(_cmd: &mut Command, ids: &Vec<i64>, tags: &Vec<String>) -> anyhow::Result<()> {
     if !tags.is_empty() {
         return Err(anyhow::anyhow!("Tags are not supported with --diff. Please provide exactly two IDs."));
     }
@@ -126,3 +85,49 @@ fn setup_diff_paths_and_compression(
 
     Ok((item_a_path, item_b_path))
 }
+
+pub fn mode_diff(
+    cmd: &mut Command,
+    args: &crate::args::Args,
+    conn: &mut rusqlite::Connection,
+) -> anyhow::Result<()> {
+    let ids: Vec<i64> = args
+        .ids_or_tags
+        .iter()
+        .filter_map(|x| {
+            if let crate::args::NumberOrString::Number(n) = x {
+                Some(*n)
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    let tags: Vec<String> = args
+        .ids_or_tags
+        .iter()
+        .filter_map(|x| {
+            if let crate::args::NumberOrString::Str(s) = x {
+                Some(s.clone())
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    validate_diff_args(cmd, &ids, &tags)?;
+
+    let settings = crate::config::Settings::new(args, crate::config::default_dir()?)?;
+
+    let item_service = crate::services::item_service::ItemService::new(&settings)?;
+
+    let (item_a, item_b) = fetch_and_validate_items(conn, &ids, &item_service)?;
+
+    let (path_a, path_b) = setup_diff_paths_and_compression(&item_service, &item_a, &item_b)?;
+
+    // TODO: Implement actual diff logic here
+    // For now, just print paths or something to make it compile
+    println!("Diff between {:?} and {:?}", path_a, path_b);
+
+    Ok(())
+}
diff --git a/src/parser/filter.pest b/src/parser/filter.pest
new file mode 100644
index 0000000..b1e5f2d
--- /dev/null
+++ b/src/parser/filter.pest
@@ -0,0 +1,41 @@
+WHITESPACE = _{ " " | "\t" | "\n" | "\r" }
+
+// This Pest grammar defines the syntax for filter chains used in the Keep application.
+
+// Main entry point for parsing multiple filters separated by pipes
+filters = { SOI ~ filter ~ (pipe ~ filter)* ~ EOI }
+
+// A single filter with optional options
+filter = { filter_name ~ options? }
+
+// Filter name (alphanumeric with underscores)
+filter_name = @{ [a-zA-Z_][a-zA-Z0-9_]* }
+
+// Options block with parentheses
+options = { "(" ~ WO ~ option* ~ WO ~ ")" }
+
+// Single option: either named (name=value) or unnamed (just value)
+option = { WO ~ (option_name ~ WO ~ "=" ~ WO ~ option_value | option_value) }
+
+// Option name (alphanumeric with underscores)
+option_name = @{ [a-zA-Z_][a-zA-Z0-9_]* }
+
+// Option value: number, boolean, or quoted string
+option_value = { number | boolean | string }
+
+// Simple number (integer or float)
+number = @{ ("-")? ~ [0-9]+ ~ ('.' ~ [0-9]+)? }
+
+// Boolean true or false
+boolean = { "true" | "false" }
+
+// Quoted string (double or single quotes)
+string = { (dquote ~ (!dquote ~ [^"])* ~ dquote) | (squote ~ (!squote ~ [^'])* ~ squote) }
+dquote = { '"' }
+squote = { '\'' }
+
+// Pipe separator
+pipe = { "|" }
+
+// Optional whitespace
+WO = { (WHITESPACE)* }