diff --git a/Sources/ForceSimulation/forces/CenterForce.swift b/Sources/ForceSimulation/forces/CenterForce.swift
index 4353d68..7356669 100644
--- a/Sources/ForceSimulation/forces/CenterForce.swift
+++ b/Sources/ForceSimulation/forces/CenterForce.swift
@@ -9,7 +9,7 @@ import NDTree
 /// A force that drives nodes towards the center.
 /// Center force is relatively fast, the complexity is `O(n)`,
 /// where `n` is the number of nodes.
-/// See [Collide Force - D3](https://d3js.org/d3-force/collide)
+/// See [Collide Force - D3](https://d3js.org/d3-force/collide).
 final public class CenterForce<NodeID, V>: ForceLike
 where NodeID: Hashable, V: VectorLike, V.Scalar == Double {
     public var center: V
@@ -40,6 +40,9 @@ where NodeID: Hashable, V: VectorLike, V.Scalar == Double {
 extension Simulation {
 
     /// Create a center force that drives nodes towards the center.
+    /// Center force is relatively fast, the complexity is `O(n)`,
+    /// where `n` is the number of nodes.
+    /// See [Collide Force - D3](https://d3js.org/d3-force/collide).
     /// - Parameters:
     ///  - center: The center of the force.
     ///  - strength: The strength of the force.
diff --git a/Sources/ForceSimulation/forces/CollideForce.swift b/Sources/ForceSimulation/forces/CollideForce.swift
index acf429f..4a88281 100644
--- a/Sources/ForceSimulation/forces/CollideForce.swift
+++ b/Sources/ForceSimulation/forces/CollideForce.swift
@@ -43,7 +43,7 @@ struct MaxRadiusTreeDelegate<NodeID, V>: NDTreeDelegate where NodeID: Hashable,
 /// A force that prevents nodes from overlapping.
 /// This is a very expensive force, the complexity is `O(n log(n))`,
 /// where `n` is the number of nodes. 
-/// See [Collide Force - D3](https://d3js.org/d3-force/collide)
+/// See [Collide Force - D3](https://d3js.org/d3-force/collide).
 public final class CollideForce<NodeID, V>: ForceLike
 where NodeID: Hashable, V: VectorLike, V.Scalar == Double {
 
@@ -184,7 +184,7 @@ extension Simulation {
     /// Create a collide force that prevents nodes from overlapping.
     /// This is a very expensive force, the complexity is `O(n log(n))`,
     /// where `n` is the number of nodes. 
-    /// See [Collide Force - D3](https://d3js.org/d3-force/collide)
+    /// See [Collide Force - D3](https://d3js.org/d3-force/collide).
     /// - Parameters:
     ///   - radius: The radius of the force.
     ///   - strength: The strength of the force.
diff --git a/Sources/ForceSimulation/forces/LinkForce.swift b/Sources/ForceSimulation/forces/LinkForce.swift
index 70ad1d4..92f2b28 100644
--- a/Sources/ForceSimulation/forces/LinkForce.swift
+++ b/Sources/ForceSimulation/forces/LinkForce.swift
@@ -13,7 +13,7 @@ enum LinkForceError: Error {
 
 /// A force that represents links between nodes.
 /// The complexity is `O(e)`, where `e` is the number of links.
-/// See [Link Force - D3](https://d3js.org/d3-force/link)
+/// See [Link Force - D3](https://d3js.org/d3-force/link).
 final public class LinkForce<NodeID, V>: ForceLike
 where NodeID: Hashable, V: VectorLike, V.Scalar == Double {
 
@@ -224,7 +224,7 @@ extension Simulation {
     /// Create a link force that represents links between nodes. It works like
     /// there is a spring between each pair of nodes.
     /// The complexity is `O(e)`, where `e` is the number of links.
-    /// See [Link Force - D3](https://d3js.org/d3-force/link)
+    /// See [Link Force - D3](https://d3js.org/d3-force/link).
     /// - Parameters:
     ///  - links: The links between nodes.
     ///  - stiffness: The stiffness of the spring (or links).
diff --git a/Sources/ForceSimulation/forces/ManyBodyForce.swift b/Sources/ForceSimulation/forces/ManyBodyForce.swift
index 2af5365..381d830 100644
--- a/Sources/ForceSimulation/forces/ManyBodyForce.swift
+++ b/Sources/ForceSimulation/forces/ManyBodyForce.swift
@@ -77,7 +77,7 @@ struct MassQuadtreeDelegate<NodeID, V>: NDTreeDelegate where NodeID: Hashable, V
 /// A force that simulate the many-body force. 
 /// This is a very expensive force, the complexity is `O(n log(n))`,
 /// where `n` is the number of nodes. The complexity might degrade to `O(n^2)` if the nodes are too close to each other.
-/// See [Manybody Force - D3](https://d3js.org/d3-force/many-body)
+/// See [Manybody Force - D3](https://d3js.org/d3-force/many-body).
 final public class ManyBodyForce<NodeID, V>: ForceLike
 where NodeID: Hashable, V: VectorLike, V.Scalar == Double {
 
@@ -312,7 +312,7 @@ extension Simulation {
     /// This is a very expensive force, the complexity is `O(n log(n))`,
     /// where `n` is the number of nodes. The complexity might degrade to `O(n^2)` if the nodes are too close to each other.
     /// The force mimics the gravity force or electrostatic force.
-    /// See [Manybody Force - D3](https://d3js.org/d3-force/many-body)
+    /// See [Manybody Force - D3](https://d3js.org/d3-force/many-body).
     /// - Parameters:
     ///  - strength: The strength of the force. When the strength is positive, the nodes are attracted to each other like gravity force, otherwise, the nodes are repelled like electrostatic force.
     ///  - nodeMass: The mass of the nodes. The mass is used to calculate the force. The default value is 1.0.