diff --git a/book/04-tags.md b/book/04-tags.md
index 0df7386..327860f 100644
--- a/book/04-tags.md
+++ b/book/04-tags.md
@@ -218,6 +218,38 @@ impl Tags {
     pub fn has(&self, name: &str) -> bool {
         self.find(name).is_some()
     }
+
+    /// Append a tag built from a name and a list of values. Returns
+    /// `self` so the call can chain.
+    pub fn add<N, V, S>(mut self, name: N, values: V) -> Self
+    where
+        N: Into<String>,
+        V: IntoIterator<Item = S>,
+        S: Into<String>,
+    {
+        self.0.push(Tag::new(name, values));
+        self
+    }
+
+    /// Remove every tag with the given name. Returns `self` so the
+    /// call can chain.
+    pub fn remove(mut self, name: &str) -> Self {
+        self.0.retain(|t| t.name() != name);
+        self
+    }
+
+    /// Replace every tag with the given name by a single new tag
+    /// built from `name` and `values`. Equivalent to `remove(name)`
+    /// followed by `add(Tag::new(name, values))`.
+    pub fn set<N, V, S>(self, name: N, values: V) -> Self
+    where
+        N: Into<String>,
+        V: IntoIterator<Item = S>,
+        S: Into<String>,
+    {
+        let name = name.into();
+        self.remove(&name).add(name, values)
+    }
 }
 
 impl std::ops::Deref for Tags {
@@ -251,6 +283,21 @@ variants. Checking whether a collection mentions a particular pubkey
 is `tags.values("p").any(|p| p == hex)` — the code reads the way the
 question sounds.
 
+Mutation is just as flat. `add` appends a tag; `remove` drops every
+tag with a given name; `set` replaces every tag of a given name with
+a single fresh one, which is the common case when a replaceable kind
+is rewriting one of its own singleton fields. All three consume and
+return `self`, so assembling or rewriting a collection reads as one
+expression:
+
+```rust
+let tags = Tags::new()
+    .add("t", ["nostr"])   // [["t", "nostr"]]
+    .add("t", ["rust"])    // [["t", "nostr"], ["t", "rust"]]
+    .set("t", ["nothing"]) // [["t", "nothing"]]
+    .remove("t");          // []
+```
+
 ## What's next
 
 Tags are the structured-data building block that every other type in
diff --git a/book/05-events.md b/book/05-events.md
index 03812ab..d01eb2a 100644
--- a/book/05-events.md
+++ b/book/05-events.md
@@ -100,17 +100,38 @@ other events, pubkeys, topics, and whatever else. Tags and content travel
 together because tags are part of what the hash commits to — they are not
 metadata in the "could be added later" sense.
 
+`EventContent` is a builder. `new` hands back an empty payload and
+chainable `content` and `tags` setters fill it in. Neither field is
+required at construction time — a zero-length note with no tags is a
+perfectly legal kind-1 event — and the builder shape means callers
+don't have to pass `""` or `vec![]` placeholders when they only care
+about one of the two.
+
 ```rust {file=coracle-lib/src/events.rs}
 /// The content of an event: the human-readable body plus its tags.
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub struct EventContent {
     pub content: String,
     pub tags: Tags,
 }
 
 impl EventContent {
-    pub fn new(content: impl Into<String>, tags: impl Into<Tags>) -> Self {
-        EventContent { content: content.into(), tags: tags.into() }
+    /// An empty payload: no content, no tags.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Set the human-readable content. Returns `self` so the call can
+    /// chain.
+    pub fn content(mut self, content: impl Into<String>) -> Self {
+        self.content = content.into();
+        self
+    }
+
+    /// Set the tags. Returns `self` so the call can chain.
+    pub fn tags(mut self, tags: impl Into<Tags>) -> Self {
+        self.tags = tags.into();
+        self
     }
 }
 ```
@@ -324,7 +345,8 @@ With that in place, the full pipeline from "hello nostr" to a signed event is
 one expression:
 
 ```rust
-let hashed = EventContent::new("hello nostr", vec![])
+let hashed = EventContent::new()
+    .content("hello nostr")
     .kind(1)
     .stamp(1_700_000_000)
     .own(secret.public_key())
diff --git a/book/06-kinds.md b/book/06-kinds.md
index 37cf05a..2130a5b 100644
--- a/book/06-kinds.md
+++ b/book/06-kinds.md
@@ -234,7 +234,9 @@ impl Kind for Deletion {
     }
 
     fn to_content(&self) -> EventContent {
-        EventContent::new(self.reason.clone(), self.tags.clone())
+        EventContent::new()
+            .content(self.reason.clone())
+            .tags(self.tags.clone())
     }
 }
 ```
diff --git a/coracle-wasm/src/lib.rs b/coracle-wasm/src/lib.rs
index f36cd3b..2710307 100644
--- a/coracle-wasm/src/lib.rs
+++ b/coracle-wasm/src/lib.rs
@@ -192,7 +192,9 @@ impl Event {
                 .collect::<Vec<_>>(),
         );
 
-        let hashed = cev::EventContent::new(content, tags)
+        let hashed = cev::EventContent::new()
+            .content(content)
+            .tags(tags)
             .kind(kind)
             .stamp(created_at)
             .own(sk.0.public_key())