diff --git a/crates/fj-kernel/src/validate/cycle.rs b/crates/fj-kernel/src/validate/cycle.rs
index 16cc826f5..0c0442038 100644
--- a/crates/fj-kernel/src/validate/cycle.rs
+++ b/crates/fj-kernel/src/validate/cycle.rs
@@ -1,12 +1,147 @@
 use crate::objects::Cycle;
+use crate::objects::HalfEdge;
+use fj_math::Point;
+use fj_math::Scalar;
+use itertools::Itertools;
 
 use super::{Validate, ValidationConfig, ValidationError};
 
 impl Validate for Cycle {
     fn validate_with_config(
         &self,
-        _: &ValidationConfig,
-        _: &mut Vec<ValidationError>,
+        config: &ValidationConfig,
+        errors: &mut Vec<ValidationError>,
     ) {
+        CycleValidationError::check_half_edges_disconnected(
+            self, config, errors,
+        );
+        CycleValidationError::check_enough_half_edges(self, config, errors);
+    }
+}
+
+/// [`Cycle`] validation failed
+#[derive(Clone, Debug, thiserror::Error)]
+pub enum CycleValidationError {
+    /// [`Cycle`]'s half-edges are not connected
+    #[error(
+        "Adjacent `HalfEdge`s are distinct\n\
+        - End position of first `HalfEdge`: {end_of_first:?}\n\
+        - Start position of second `HalfEdge`: {start_of_second:?}\n\
+        - `HalfEdge`s: {half_edges:#?}"
+    )]
+    HalfEdgesDisconnected {
+        /// The end position of the first [`HalfEdge`]
+        end_of_first: Point<2>,
+
+        /// The start position of the second [`HalfEdge`]
+        start_of_second: Point<2>,
+
+        /// The distance between the two vertices
+        distance: Scalar,
+
+        /// The half-edge
+        half_edges: Box<(HalfEdge, HalfEdge)>,
+    },
+    #[error("Expected at least one `HalfEdge`\n")]
+    NotEnoughHalfEdges,
+}
+
+impl CycleValidationError {
+    fn check_enough_half_edges(
+        cycle: &Cycle,
+        _config: &ValidationConfig,
+        errors: &mut Vec<ValidationError>,
+    ) {
+        // If there are no half edges
+        if cycle.half_edges().next().is_none() {
+            errors.push(Self::NotEnoughHalfEdges.into());
+        }
+    }
+
+    fn check_half_edges_disconnected(
+        cycle: &Cycle,
+        config: &ValidationConfig,
+        errors: &mut Vec<ValidationError>,
+    ) {
+        for (first, second) in cycle.half_edges().circular_tuple_windows() {
+            let end_of_first = {
+                let [_, end] = first.boundary();
+                first.curve().point_from_path_coords(end)
+            };
+            let start_of_second = second.start_position();
+
+            let distance = (end_of_first - start_of_second).magnitude();
+
+            if distance > config.identical_max_distance {
+                errors.push(
+                    Self::HalfEdgesDisconnected {
+                        end_of_first,
+                        start_of_second,
+                        distance,
+                        half_edges: Box::new((
+                            first.clone_object(),
+                            second.clone_object(),
+                        )),
+                    }
+                    .into(),
+                );
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use crate::{
+        builder::{CycleBuilder, HalfEdgeBuilder},
+        objects::Cycle,
+        services::Services,
+        validate::{cycle::CycleValidationError, Validate, ValidationError},
+    };
+
+    #[test]
+    fn half_edges_connected() -> anyhow::Result<()> {
+        let mut services = Services::new();
+
+        let valid = Cycle::new([])
+            .update_as_polygon_from_points(
+                [[0.0, 0.0], [1.0, 0.0], [1.0, 1.0]],
+                &mut services.objects,
+            )
+            .0;
+
+        valid.validate_and_return_first_error()?;
+
+        let disconnected = {
+            let first =
+                HalfEdgeBuilder::line_segment([[0., 0.], [1., 0.]], None)
+                    .build(&mut services.objects);
+            let second =
+                HalfEdgeBuilder::line_segment([[0., 0.], [1., 0.]], None)
+                    .build(&mut services.objects);
+
+            Cycle::new([])
+                .add_half_edge(first, &mut services.objects)
+                .0
+                .add_half_edge(second, &mut services.objects)
+                .0
+        };
+        assert!(matches!(
+            disconnected.validate_and_return_first_error(),
+            Err(ValidationError::Cycle(
+                CycleValidationError::HalfEdgesDisconnected { .. }
+            ))
+        ));
+
+        let empty = Cycle::new([]);
+        assert!(matches!(
+            empty.validate_and_return_first_error(),
+            Err(ValidationError::Cycle(
+                CycleValidationError::NotEnoughHalfEdges
+            ))
+        ));
+
+        Ok(())
     }
 }
diff --git a/crates/fj-kernel/src/validate/mod.rs b/crates/fj-kernel/src/validate/mod.rs
index f45bfbd5b..5a0dcfc84 100644
--- a/crates/fj-kernel/src/validate/mod.rs
+++ b/crates/fj-kernel/src/validate/mod.rs
@@ -9,6 +9,7 @@ mod solid;
 mod surface;
 mod vertex;
 
+use self::cycle::CycleValidationError;
 pub use self::{edge::HalfEdgeValidationError, face::FaceValidationError};
 
 use std::convert::Infallible;
@@ -87,6 +88,10 @@ pub enum ValidationError {
     /// `HalfEdge` validation error
     #[error("`HalfEdge` validation error:\n{0}")]
     HalfEdge(#[from] HalfEdgeValidationError),
+
+    /// `Cycle` validation error
+    #[error("`Cycle` validation error:\n{0}")]
+    Cycle(#[from] CycleValidationError),
 }
 
 impl From<Infallible> for ValidationError {