diff --git a/.changeset/nice-moons-run.md b/.changeset/nice-moons-run.md
new file mode 100644
index 0000000000..0096d51788
--- /dev/null
+++ b/.changeset/nice-moons-run.md
@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+expose .length property on MutableList
diff --git a/packages/effect/src/MutableList.ts b/packages/effect/src/MutableList.ts
index 1027aaaa5c..2009bc8cd8 100644
--- a/packages/effect/src/MutableList.ts
+++ b/packages/effect/src/MutableList.ts
@@ -21,6 +21,7 @@ export type TypeId = typeof TypeId
  */
 export interface MutableList<out A> extends Iterable<A>, Pipeable, Inspectable {
   readonly [TypeId]: TypeId
+  readonly length: number
 
   /** @internal */
   head: LinkedListNode<A> | undefined
@@ -28,7 +29,7 @@ export interface MutableList<out A> extends Iterable<A>, Pipeable, Inspectable {
   tail: LinkedListNode<A> | undefined
 }
 
-const MutableListProto: Omit<MutableList<unknown>, "head" | "tail"> = {
+const MutableListProto: Omit<MutableList<unknown>, "head" | "tail" | "length"> = {
   [TypeId]: TypeId,
   [Symbol.iterator](this: MutableList<unknown>): Iterator<unknown> {
     let done = false
@@ -72,7 +73,7 @@ const MutableListProto: Omit<MutableList<unknown>, "head" | "tail"> = {
 }
 
 interface MutableListImpl<A> extends MutableList<A> {
-  _length: number
+  length: number
 }
 
 /** @internal */
@@ -101,7 +102,7 @@ export const empty = <A>(): MutableList<A> => {
   const list = Object.create(MutableListProto)
   list.head = undefined
   list.tail = undefined
-  list._length = 0
+  list.length = 0
   return list
 }
 
@@ -141,7 +142,7 @@ export const isEmpty = <A>(self: MutableList<A>): boolean => length(self) === 0
  * @since 2.0.0
  * @category getters
  */
-export const length = <A>(self: MutableList<A>): number => (self as MutableListImpl<A>)._length
+export const length = <A>(self: MutableList<A>): number => (self as MutableListImpl<A>).length
 
 /**
  * Returns the last element of the list, if it exists.
@@ -185,7 +186,7 @@ export const forEach: {
  * @since 2.0.0
  */
 export const reset = <A>(self: MutableList<A>): MutableList<A> => {
-  ;(self as MutableListImpl<A>)._length = 0
+  ;(self as MutableListImpl<A>).length = 0
   self.head = undefined
   self.tail = undefined
   return self
@@ -215,7 +216,7 @@ export const append: {
     node.prev = self.tail
     self.tail = node
   }
-  ;(self as MutableListImpl<A>)._length += 1
+  ;(self as MutableListImpl<A>).length += 1
   return self
 })
 
@@ -269,7 +270,7 @@ export const prepend: {
   if (self.tail === undefined) {
     self.tail = node
   }
-  ;(self as MutableListImpl<A>)._length += 1
+  ;(self as MutableListImpl<A>).length += 1
   return self
 })
 
@@ -291,7 +292,7 @@ const remove = <A>(self: MutableList<A>, node: LinkedListNode<A>): void => {
     self.tail = undefined
     self.head = undefined
   }
-  if ((self as MutableListImpl<A>)._length > 0) {
-    ;(self as MutableListImpl<A>)._length -= 1
+  if ((self as MutableListImpl<A>).length > 0) {
+    ;(self as MutableListImpl<A>).length -= 1
   }
 }
diff --git a/packages/effect/src/internal/mailbox.ts b/packages/effect/src/internal/mailbox.ts
index 875de46fbc..07b8d40d63 100644
--- a/packages/effect/src/internal/mailbox.ts
+++ b/packages/effect/src/internal/mailbox.ts
@@ -54,8 +54,6 @@ type MailboxState<A, E> = {
   readonly exit: Exit<void, E>
 }
 
-const asDone = core.exitAs([[] as Array<never>, true] as const)
-
 class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
   readonly [TypeId]: Api.TypeId = TypeId
   readonly [ReadonlyTypeId]: Api.ReadonlyTypeId = ReadonlyTypeId
@@ -145,8 +143,7 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
     return core.suspend(() => {
       if (this.state._tag !== "Open") {
         return core.succeed(false)
-      }
-      if (MutableList.length(this.messages) >= this.capacity) {
+      } else if (this.messages.length >= this.capacity) {
         return core.map(this.offerRemaining([message]), Arr.isEmptyArray)
       }
       MutableList.append(this.messages, message)
@@ -157,8 +154,7 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
   unsafeOffer(message: A): boolean {
     if (this.state._tag !== "Open") {
       return false
-    }
-    if (MutableList.length(this.messages) >= this.capacity) {
+    } else if (this.messages.length >= this.capacity) {
       return false
     }
     MutableList.append(this.messages, message)
@@ -181,7 +177,7 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
     if (this.state._tag !== "Open") {
       return Arr.fromIterable(messages)
     }
-    const free = this.capacity - MutableList.length(this.messages)
+    const free = this.capacity - this.messages.length
     if (free === 0) {
       return Arr.fromIterable(messages)
     }
@@ -234,7 +230,7 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
   }
   end = this.done(core.exitVoid)
   takeAll: Effect<readonly [messages: Array<A>, done: boolean], E> = core.suspend(() => {
-    const len = MutableList.length(this.messages)
+    const len = this.messages.length
     if (len > 0) {
       const messages = listToArray(this.messages, len)
       MutableList.reset(this.messages)
@@ -244,17 +240,19 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
       this.releaseCapacity(len)
       return core.succeed([messages, false])
     } else if (this.state._tag === "Done") {
-      return asDone(this.state.exit)
+      return core.exitAs(this.state.exit, [[], true])
     }
     return core.zipRight(this.awaitTake, this.takeAll)
   })
   takeN(n: number): Effect<readonly [messages: Array<A>, done: boolean], E> {
     return core.suspend(() => {
       if (n <= 0) {
-        return this.state._tag === "Done" ? asDone(this.state.exit) : core.succeed([[], false])
+        return this.state._tag === "Done"
+          ? core.exitAs(this.state.exit, [[], true])
+          : core.succeed([[], false])
       }
       n = Math.min(n, this.capacity)
-      if (n <= MutableList.length(this.messages)) {
+      if (n <= this.messages.length) {
         const messages = new Array<A>(n)
         for (let i = 0; i < n; i++) {
           messages[i] = MutableList.shift(this.messages)!
@@ -269,7 +267,7 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
     })
   }
   take: Effect<Option.Option<A>, E> = core.suspend(() => {
-    if (MutableList.length(this.messages) > 0) {
+    if (this.messages.length > 0) {
       const message = MutableList.shift(this.messages)!
       this.releaseCapacity(1)
       return core.succeed(Option.some(message))
@@ -290,7 +288,7 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
     })
   })
   unsafeSize(): Option.Option<number> {
-    return this.state._tag !== "Done" ? Option.some(MutableList.length(this.messages)) : Option.none()
+    return this.state._tag !== "Done" ? Option.some(this.messages.length) : Option.none()
   }
   size = core.sync(() => this.unsafeSize())
 }