diff --git a/rhio-client/src/lib.rs b/rhio-client/src/lib.rs
index d1ad027..cdb1a1d 100644
--- a/rhio-client/src/lib.rs
+++ b/rhio-client/src/lib.rs
@@ -1,8 +1,10 @@
 use anyhow::Result;
 use async_nats::jetstream::Context;
-use p2panda_core::PrivateKey;
+use p2panda_core::{Hash, PrivateKey};
 use p2panda_store::MemoryStore;
-use rhio_core::{create_message, encode_operation, LogId, RhioExtensions};
+use rhio_core::{
+    create_blob_announcement, create_message, encode_operation, LogId, RhioExtensions,
+};
 
 pub struct Client {
     jetstream: JetStream,
@@ -33,6 +35,14 @@ impl Client {
         self.jetstream.publish(subject, encoded_operation).await?;
         Ok(())
     }
+
+    pub async fn announce_blob(&mut self, subject: String, hash: Hash) -> Result<()> {
+        let operation =
+            create_blob_announcement(&mut self.store, &self.private_key, &subject, hash)?;
+        let encoded_operation = encode_operation(operation.header, operation.body)?;
+        self.jetstream.publish(subject, encoded_operation).await?;
+        Ok(())
+    }
 }
 
 pub struct JetStream {
diff --git a/rhio-client/src/main.rs b/rhio-client/src/main.rs
index 6532864..99bc10f 100644
--- a/rhio-client/src/main.rs
+++ b/rhio-client/src/main.rs
@@ -1,5 +1,8 @@
+use std::str::FromStr;
+
 use anyhow::{Context, Result};
 use clap::Parser;
+use p2panda_core::Hash;
 use rhio_client::Client;
 use tokio::sync::mpsc;
 
@@ -35,9 +38,19 @@ async fn main() -> Result<()> {
     loop {
         tokio::select! {
             Some(payload) = line_rx.recv() => {
-                client
-                    .publish(args.subject.clone(), payload.as_bytes())
-                    .await?;
+                // If user writes a string, starting with "blob" (4 characters), followed by a
+                // space (1 character) and then ending with an hex-encoded BLAKE3 hash (64
+                // characters), then we interpret this as a blob announcement!
+                if payload.len() == 4 + 1 + 64 && payload.to_lowercase().starts_with("blob") {
+                    let file_name = &payload[5..];
+                    client
+                        .announce_blob(args.subject.clone(), file_name)
+                        .await?;
+                } else {
+                    client
+                        .publish(args.subject.clone(), payload.as_bytes())
+                        .await?;
+                }
             }
             _ = tokio::signal::ctrl_c() => {
                 break;
diff --git a/rhio-core/src/operation.rs b/rhio-core/src/operation.rs
index f1863bc..de426e0 100644
--- a/rhio-core/src/operation.rs
+++ b/rhio-core/src/operation.rs
@@ -13,12 +13,12 @@ pub fn create_blob_announcement<S>(
     store: &mut S,
     private_key: &PrivateKey,
     subject: &str,
-    blob_hash: Option<Hash>,
+    blob_hash: Hash,
 ) -> Result<Operation<RhioExtensions>>
 where
     S: OperationStore<LogId, RhioExtensions> + LogStore<LogId, RhioExtensions>,
 {
-    create_operation(store, private_key, subject, blob_hash, None)
+    create_operation(store, private_key, subject, Some(blob_hash), None)
 }
 
 pub fn create_message<S>(