diff --git a/lcli/src/http_sync.rs b/lcli/src/http_sync.rs
new file mode 100644
index 00000000000..1ef40e63978
--- /dev/null
+++ b/lcli/src/http_sync.rs
@@ -0,0 +1,152 @@
+use clap::ArgMatches;
+use clap_utils::{parse_optional, parse_required};
+use environment::Environment;
+use eth2::{
+    types::{BlockId, ChainSpec, ForkName, PublishBlockRequest, SignedBlockContents},
+    BeaconNodeHttpClient, Error, SensitiveUrl, Timeouts,
+};
+use eth2_network_config::Eth2NetworkConfig;
+use ssz::Encode;
+use std::fs;
+use std::fs::File;
+use std::io::{Read, Write};
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+use std::time::Duration;
+use types::EthSpec;
+
+const HTTP_TIMEOUT: Duration = Duration::from_secs(3600);
+const DEFAULT_CACHE_DIR: &str = "./cache";
+
+pub fn run<T: EthSpec>(
+    env: Environment<T>,
+    network_config: Eth2NetworkConfig,
+    matches: &ArgMatches,
+) -> Result<(), String> {
+    let executor = env.core_context().executor;
+    executor
+        .handle()
+        .ok_or("shutdown in progress")?
+        .block_on(async move { run_async::<T>(network_config, matches).await })
+}
+
+pub async fn run_async<T: EthSpec>(
+    network_config: Eth2NetworkConfig,
+    matches: &ArgMatches,
+) -> Result<(), String> {
+    let spec = &network_config.chain_spec::<T>()?;
+    let source_url: SensitiveUrl = parse_required(matches, "source-url")?;
+    let target_url: SensitiveUrl = parse_required(matches, "target-url")?;
+    let start_block: BlockId = parse_required(matches, "start-block")?;
+    let maybe_common_ancestor_block: Option<BlockId> =
+        parse_optional(matches, "known–common-ancestor")?;
+    let cache_dir_path: PathBuf =
+        parse_optional(matches, "block-cache-dir")?.unwrap_or(DEFAULT_CACHE_DIR.into());
+
+    let source = BeaconNodeHttpClient::new(source_url, Timeouts::set_all(HTTP_TIMEOUT));
+    let target = BeaconNodeHttpClient::new(target_url, Timeouts::set_all(HTTP_TIMEOUT));
+
+    if !cache_dir_path.exists() {
+        fs::create_dir_all(&cache_dir_path)
+            .map_err(|e| format!("Unable to create block cache dir: {:?}", e))?;
+    }
+
+    // 1. Download blocks back from head, looking for common ancestor.
+    let mut blocks = vec![];
+    let mut next_block_id = start_block;
+    loop {
+        println!("downloading {next_block_id:?}");
+
+        let publish_block_req =
+            get_block_from_source::<T>(&source, next_block_id, spec, &cache_dir_path).await;
+        let block = publish_block_req.signed_block();
+
+        next_block_id = BlockId::Root(block.parent_root());
+        blocks.push((block.slot(), publish_block_req));
+
+        if let Some(ref common_ancestor_block) = maybe_common_ancestor_block {
+            if common_ancestor_block == &next_block_id {
+                println!("reached known common ancestor: {next_block_id:?}");
+                break;
+            }
+        }
+
+        let block_exists_in_target = target
+            .get_beacon_blocks_ssz::<T>(next_block_id, spec)
+            .await
+            .unwrap()
+            .is_some();
+        if block_exists_in_target {
+            println!("common ancestor found: {next_block_id:?}");
+            break;
+        }
+    }
+
+    // 2. Apply blocks to target.
+    for (slot, block) in blocks.iter().rev() {
+        println!("posting block at slot {slot}");
+        if let Err(e) = target.post_beacon_blocks(block).await {
+            if let Error::ServerMessage(ref e) = e {
+                if e.code == 202 {
+                    println!("duplicate block detected while posting block at slot {slot}");
+                    continue;
+                }
+            }
+            return Err(format!("error posting {slot}: {e:?}"));
+        } else {
+            println!("success");
+        }
+    }
+
+    println!("SYNCED!!!!");
+
+    Ok(())
+}
+
+async fn get_block_from_source<T: EthSpec>(
+    source: &BeaconNodeHttpClient,
+    block_id: BlockId,
+    spec: &ChainSpec,
+    cache_dir_path: &Path,
+) -> PublishBlockRequest<T> {
+    let mut cache_path = cache_dir_path.join(format!("block_{block_id}"));
+
+    if cache_path.exists() {
+        let mut f = File::open(&cache_path).unwrap();
+        let mut bytes = vec![];
+        f.read_to_end(&mut bytes).unwrap();
+        PublishBlockRequest::from_ssz_bytes(&bytes, ForkName::Deneb).unwrap()
+    } else {
+        let block_from_source = source
+            .get_beacon_blocks_ssz::<T>(block_id, spec)
+            .await
+            .unwrap()
+            .unwrap();
+        let blobs_from_source = source
+            .get_blobs::<T>(block_id, None)
+            .await
+            .unwrap()
+            .unwrap()
+            .data;
+
+        let (kzg_proofs, blobs): (Vec<_>, Vec<_>) = blobs_from_source
+            .iter()
+            .cloned()
+            .map(|sidecar| (sidecar.kzg_proof, sidecar.blob.clone()))
+            .unzip();
+
+        let block_root = block_from_source.canonical_root();
+        let block_contents = SignedBlockContents {
+            signed_block: Arc::new(block_from_source),
+            kzg_proofs: kzg_proofs.into(),
+            blobs: blobs.into(),
+        };
+        let publish_block_req = PublishBlockRequest::BlockContents(block_contents);
+
+        cache_path = cache_dir_path.join(format!("block_{block_root:?}"));
+        let mut f = File::create(&cache_path).unwrap();
+        f.write_all(&publish_block_req.as_ssz_bytes()).unwrap();
+
+        publish_block_req
+    }
+}
diff --git a/lcli/src/main.rs b/lcli/src/main.rs
index 85898b60ee4..380aeb6aceb 100644
--- a/lcli/src/main.rs
+++ b/lcli/src/main.rs
@@ -1,6 +1,7 @@
 mod block_root;
 mod check_deposit_data;
 mod generate_bootnode_enr;
+mod http_sync;
 mod indexed_attestations;
 mod mnemonic_validators;
 mod mock_el;
@@ -552,6 +553,74 @@ fn main() {
                         .display_order(0)
                 )
         )
+        .subcommand(
+            Command::new("http-sync")
+                .about("Manual sync")
+                .arg(
+                    Arg::new("start-block")
+                        .long("start-block")
+                        .value_name("BLOCK_ID")
+                        .action(ArgAction::Set)
+                        .help("Block ID of source's head")
+                        .default_value("head")
+                        .required(true)
+                        .display_order(0)
+                )
+                .arg(
+                    Arg::new("source-url")
+                        .long("source-url")
+                        .value_name("URL")
+                        .action(ArgAction::Set)
+                        .help("URL to a synced beacon-API provider")
+                        .required(true)
+                        .display_order(0)
+                )
+                .arg(
+                    Arg::new("target-url")
+                        .long("target-url")
+                        .value_name("URL")
+                        .action(ArgAction::Set)
+                        .help("URL to an unsynced beacon-API provider")
+                        .required(true)
+                        .display_order(0)
+                )
+                .arg(
+                    Arg::new("testnet-dir")
+                        .short('d')
+                        .long("testnet-dir")
+                        .value_name("PATH")
+                        .action(ArgAction::Set)
+                        .global(true)
+                        .help("The testnet dir.")
+                        .display_order(0)
+                )
+                .arg(
+                    Arg::new("network")
+                        .long("network")
+                        .value_name("NAME")
+                        .action(ArgAction::Set)
+                        .global(true)
+                        .help("The network to use. Defaults to mainnet.")
+                        .conflicts_with("testnet-dir")
+                        .display_order(0)
+                )
+                .arg(
+                    Arg::new("known-common-ancestor")
+                        .long("known-common-ancestor")
+                        .value_name("BLOCK_ID")
+                        .action(ArgAction::Set)
+                        .help("Block ID of common ancestor, if known.")
+                        .display_order(0)
+                )
+                .arg(
+                    Arg::new("block-cache-dir")
+                        .long("block-cache-dir")
+                        .value_name("PATH")
+                        .action(ArgAction::Set)
+                        .help("Directory to keep a cache of the downloaded SSZ blocks.")
+                        .display_order(0)
+                )
+        )
         .get_matches();
 
     let result = matches
@@ -656,6 +725,11 @@ fn run<E: EthSpec>(env_builder: EnvironmentBuilder<E>, matches: &ArgMatches) ->
         }
         Some(("mock-el", matches)) => mock_el::run::<E>(env, matches)
             .map_err(|e| format!("Failed to run mock-el command: {}", e)),
+        Some(("http-sync", matches)) => {
+            let network_config = get_network_config()?;
+            http_sync::run::<E>(env, network_config, matches)
+                .map_err(|e| format!("Failed to run http-sync command: {}", e))
+        }
         Some((other, _)) => Err(format!("Unknown subcommand {}. See --help.", other)),
         _ => Err("No subcommand provided. See --help.".to_string()),
     }