diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9700c7f75b..c9b3651252 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### New features
 
+* New web-based `:builtin-web` diff editor. Try it with `jj split --tool
+  :builtin-web`.
+
+* The `:builtin` diff editor now has an alias `:builtin-tui`.
+
 * `jj tag list` now prints commit summary along with the tag name.
 
 * Conflict markers now include an explanation of what each part of the conflict
diff --git a/Cargo.lock b/Cargo.lock
index a9249eae9d..befe1810eb 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -195,6 +195,12 @@ dependencies = [
  "rustc-demangle",
 ]
 
+[[package]]
+name = "base64"
+version = "0.21.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d297deb1925b89f2ccc13d7635fa0714f12c87adce1c75356b39ca9b7178567"
+
 [[package]]
 name = "bitflags"
 version = "1.3.2"
@@ -327,6 +333,12 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
+[[package]]
+name = "cfg_aliases"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fd16c4719339c4530435d38e511904438d07cce7950afa3718a84ac36c10e89e"
+
 [[package]]
 name = "chrono"
 version = "0.4.38"
@@ -468,7 +480,7 @@ dependencies = [
  "nom",
  "pathdiff",
  "serde",
- "toml",
+ "toml 0.5.11",
 ]
 
 [[package]]
@@ -655,6 +667,26 @@ version = "0.1.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "56254986775e3233ffa9c4d7d3faaf6d36a2c09d30b20687e9f88bc8bafc16c8"
 
+[[package]]
+name = "diffedit3"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f26192bc4a31bef4c22e15e2b66d9278bd380f8e0a3f00dc48d18680d4f3c16"
+dependencies = [
+ "clap",
+ "indexmap",
+ "open",
+ "parking_lot",
+ "poem",
+ "rust-embed",
+ "serde",
+ "thiserror",
+ "tokio",
+ "toml 0.8.12",
+ "tracing-subscriber",
+ "walkdir",
+]
+
 [[package]]
 name = "difflib"
 version = "0.4.0"
@@ -1470,6 +1502,25 @@ dependencies = [
  "regex-syntax 0.8.3",
 ]
 
+[[package]]
+name = "h2"
+version = "0.4.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "816ec7294445779408f36fe57bc5b7fc1cf59664059096c65f905c1c61f58069"
+dependencies = [
+ "bytes 1.6.0",
+ "fnv",
+ "futures-core",
+ "futures-sink",
+ "futures-util",
+ "http",
+ "indexmap",
+ "slab",
+ "tokio",
+ "tokio-util 0.7.10",
+ "tracing",
+]
+
 [[package]]
 name = "half"
 version = "2.4.0"
@@ -1490,6 +1541,30 @@ dependencies = [
  "allocator-api2",
 ]
 
+[[package]]
+name = "headers"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "322106e6bd0cba2d5ead589ddb8150a13d7c4217cf80d7c4f682ca994ccc6aa9"
+dependencies = [
+ "base64",
+ "bytes 1.6.0",
+ "headers-core",
+ "http",
+ "httpdate",
+ "mime",
+ "sha1",
+]
+
+[[package]]
+name = "headers-core"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "54b4a22553d4242c49fddb9ba998a99962b5cc6f22cb5a3482bec22522403ce4"
+dependencies = [
+ "http",
+]
+
 [[package]]
 name = "heck"
 version = "0.4.1"
@@ -1523,6 +1598,88 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "http"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "21b9ddb458710bc376481b842f5da65cdf31522de232c1ca8146abce2a358258"
+dependencies = [
+ "bytes 1.6.0",
+ "fnv",
+ "itoa",
+]
+
+[[package]]
+name = "http-body"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1cac85db508abc24a2e48553ba12a996e87244a0395ce011e62b37158745d643"
+dependencies = [
+ "bytes 1.6.0",
+ "http",
+]
+
+[[package]]
+name = "http-body-util"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0475f8b2ac86659c21b64320d5d653f9efe42acd2a4e560073ec61a155a34f1d"
+dependencies = [
+ "bytes 1.6.0",
+ "futures-core",
+ "http",
+ "http-body",
+ "pin-project-lite",
+]
+
+[[package]]
+name = "httparse"
+version = "1.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d897f394bad6a705d5f4104762e116a75639e470d80901eed05a860a95cb1904"
+
+[[package]]
+name = "httpdate"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "df3b46402a9d5adb4c86a0cf463f42e19994e3ee891101b1841f30a545cb49a9"
+
+[[package]]
+name = "hyper"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "186548d73ac615b32a73aafe38fb4f56c0d340e110e5a200bcadbaf2e199263a"
+dependencies = [
+ "bytes 1.6.0",
+ "futures-channel",
+ "futures-util",
+ "h2",
+ "http",
+ "http-body",
+ "httparse",
+ "httpdate",
+ "itoa",
+ "pin-project-lite",
+ "smallvec",
+ "tokio",
+]
+
+[[package]]
+name = "hyper-util"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca38ef113da30126bbff9cd1705f9273e15d45498615d138b0c20279ac7a76aa"
+dependencies = [
+ "bytes 1.6.0",
+ "futures-util",
+ "http",
+ "http-body",
+ "hyper",
+ "pin-project-lite",
+ "socket2",
+ "tokio",
+]
+
 [[package]]
 name = "iana-time-zone"
 version = "0.1.60"
@@ -1580,6 +1737,7 @@ checksum = "168fb715dda47215e360912c096649d23d58bf392ac62f73919e831745e40f26"
 dependencies = [
  "equivalent",
  "hashbrown",
+ "serde",
 ]
 
 [[package]]
@@ -1619,6 +1777,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "is-docker"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "928bae27f42bc99b60d9ac7334e3a21d10ad8f1835a4e12ec3ec0464765ed1b3"
+dependencies = [
+ "once_cell",
+]
+
 [[package]]
 name = "is-terminal"
 version = "0.4.12"
@@ -1630,6 +1797,16 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "is-wsl"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "173609498df190136aa7dea1a91db051746d339e18476eed5ca40521f02d7aa5"
+dependencies = [
+ "is-docker",
+ "once_cell",
+]
+
 [[package]]
 name = "itertools"
 version = "0.10.5"
@@ -1681,6 +1858,7 @@ dependencies = [
  "config",
  "criterion",
  "crossterm",
+ "diffedit3",
  "dirs",
  "esl01-renderdag",
  "futures 0.3.30",
@@ -1712,7 +1890,7 @@ dependencies = [
  "textwrap",
  "thiserror",
  "timeago",
- "toml_edit",
+ "toml_edit 0.19.15",
  "tracing",
  "tracing-chrome",
  "tracing-subscriber",
@@ -1932,6 +2110,22 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "mime"
+version = "0.3.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6877bb514081ee2a7ff5ef9de3281f14a4dd4bceac4c09388074a6b5df8a139a"
+
+[[package]]
+name = "mime_guess"
+version = "2.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4192263c238a5f0d0c6bfd21f336a313a4ce1c450542449ca191bb657b4642ef"
+dependencies = [
+ "mime",
+ "unicase",
+]
+
 [[package]]
 name = "minimal-lexical"
 version = "0.2.1"
@@ -1980,6 +2174,18 @@ version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "defc4c55412d89136f966bbb339008b474350e5e6e78d2714439c386b3137a03"
 
+[[package]]
+name = "nix"
+version = "0.28.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ab2156c4fce2f8df6c499cc1c763e4394b7482525bf2a9701c9d79d215f519e4"
+dependencies = [
+ "bitflags 2.5.0",
+ "cfg-if",
+ "cfg_aliases",
+ "libc",
+]
+
 [[package]]
 name = "nom"
 version = "7.1.3"
@@ -2058,6 +2264,17 @@ version = "11.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0ab1bc2a289d34bd04a330323ac98a1b4bc82c9d9fcb1e66b63caa84da26b575"
 
+[[package]]
+name = "open"
+version = "5.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "449f0ff855d85ddbf1edd5b646d65249ead3f5e422aaa86b7d2d0b049b103e32"
+dependencies = [
+ "is-wsl",
+ "libc",
+ "pathdiff",
+]
+
 [[package]]
 name = "openssl-probe"
 version = "0.1.5"
@@ -2240,6 +2457,54 @@ dependencies = [
  "plotters-backend",
 ]
 
+[[package]]
+name = "poem"
+version = "3.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b735eaaaa6bc7ed2dcbcab1d5373afe1f6d03a37d8695ba3c42101f733a8455"
+dependencies = [
+ "bytes 1.6.0",
+ "futures-util",
+ "headers",
+ "hex",
+ "http",
+ "http-body-util",
+ "hyper",
+ "hyper-util",
+ "mime",
+ "mime_guess",
+ "nix",
+ "parking_lot",
+ "percent-encoding",
+ "pin-project-lite",
+ "poem-derive",
+ "regex",
+ "rfc7239",
+ "rust-embed",
+ "serde",
+ "serde_json",
+ "serde_urlencoded",
+ "smallvec",
+ "sync_wrapper",
+ "thiserror",
+ "tokio",
+ "tokio-util 0.7.10",
+ "tracing",
+ "wildmatch",
+]
+
+[[package]]
+name = "poem-derive"
+version = "3.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c2b961d58a6c53380c20236394381d9292fda03577f902b158f1638932964dcf"
+dependencies = [
+ "proc-macro-crate",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "pollster"
 version = "0.3.0"
@@ -2305,6 +2570,15 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "proc-macro-crate"
+version = "3.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6d37c51ca738a55da99dc0c4a34860fd675453b8b36209178c2249bb13651284"
+dependencies = [
+ "toml_edit 0.21.1",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.81"
@@ -2533,6 +2807,15 @@ version = "0.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "adad44e29e4c806119491a7f06f03de4d1af22c3a680dd47f1e6e179439d1f56"
 
+[[package]]
+name = "rfc7239"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b106a85eeb5b0336d16d6a20eab857f92861d4fbb1eb9a239866fb98fb6a1063"
+dependencies = [
+ "uncased",
+]
+
 [[package]]
 name = "roff"
 version = "0.2.1"
@@ -2560,6 +2843,40 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "rust-embed"
+version = "8.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fb78f46d0066053d16d4ca7b898e9343bc3530f71c61d5ad84cd404ada068745"
+dependencies = [
+ "rust-embed-impl",
+ "rust-embed-utils",
+ "walkdir",
+]
+
+[[package]]
+name = "rust-embed-impl"
+version = "8.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b91ac2a3c6c0520a3fb3dd89321177c3c692937c4eb21893378219da10c44fc8"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "rust-embed-utils",
+ "syn",
+ "walkdir",
+]
+
+[[package]]
+name = "rust-embed-utils"
+version = "8.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "86f69089032567ffff4eada41c573fc43ff466c7db7c5688b2e7969584345581"
+dependencies = [
+ "sha2",
+ "walkdir",
+]
+
 [[package]]
 name = "rustc-demangle"
 version = "0.1.23"
@@ -2685,6 +3002,29 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "serde_urlencoded"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3491c14715ca2294c4d6a88f15e84739788c1d030eed8c110436aafdaa2f3fd"
+dependencies = [
+ "form_urlencoded",
+ "itoa",
+ "ryu",
+ "serde",
+]
+
+[[package]]
+name = "sha1"
+version = "0.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3bf829a2d51ab4a5ddf1352d8470c140cadc8301b2ae1789db023f01cedd6ba"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "digest",
+]
+
 [[package]]
 name = "sha1_smol"
 version = "1.0.0"
@@ -2823,6 +3163,15 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "sync_wrapper"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "384595c11a4e2969895cad5a8c4029115f5ab956a9e5ef4de79d11a426e5f20c"
+dependencies = [
+ "futures-core",
+]
+
 [[package]]
 name = "tempfile"
 version = "3.10.1"
@@ -3049,6 +3398,20 @@ dependencies = [
  "tokio",
 ]
 
+[[package]]
+name = "tokio-util"
+version = "0.7.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5419f34732d9eb6ee4c3578b7989078579b7f039cbbb9ca2c4da015749371e15"
+dependencies = [
+ "bytes 1.6.0",
+ "futures-core",
+ "futures-sink",
+ "pin-project-lite",
+ "tokio",
+ "tracing",
+]
+
 [[package]]
 name = "toml"
 version = "0.5.11"
@@ -3058,6 +3421,19 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "toml"
+version = "0.8.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e9dd1545e8208b4a5af1aa9bbd0b4cf7e9ea08fabc5d0a5c67fcaafa17433aa3"
+dependencies = [
+ "indexmap",
+ "serde",
+ "serde_spanned",
+ "toml_datetime",
+ "toml_edit 0.22.9",
+]
+
 [[package]]
 name = "toml_datetime"
 version = "0.6.5"
@@ -3080,6 +3456,30 @@ dependencies = [
  "winnow 0.5.40",
 ]
 
+[[package]]
+name = "toml_edit"
+version = "0.21.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a8534fd7f78b5405e860340ad6575217ce99f38d4d5c8f2442cb5ecb50090e1"
+dependencies = [
+ "indexmap",
+ "toml_datetime",
+ "winnow 0.5.40",
+]
+
+[[package]]
+name = "toml_edit"
+version = "0.22.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e40bb779c5187258fd7aad0eb68cb8706a0a81fa712fbea808ab43c4b8374c4"
+dependencies = [
+ "indexmap",
+ "serde",
+ "serde_spanned",
+ "toml_datetime",
+ "winnow 0.6.5",
+]
+
 [[package]]
 name = "tracing"
 version = "0.1.40"
@@ -3173,6 +3573,24 @@ dependencies = [
  "arrayvec",
 ]
 
+[[package]]
+name = "uncased"
+version = "0.9.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e1b88fcfe09e89d3866a5c11019378088af2d24c3fbd4f0543f96b479ec90697"
+dependencies = [
+ "version_check",
+]
+
+[[package]]
+name = "unicase"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7d2d4dafb69621809a81864c9c1b864479e1235c0dd4e199924b9742439ed89"
+dependencies = [
+ "version_check",
+]
+
 [[package]]
 name = "unicode-bidi"
 version = "0.3.15"
@@ -3352,7 +3770,7 @@ dependencies = [
  "serde_bser",
  "thiserror",
  "tokio",
- "tokio-util",
+ "tokio-util 0.6.10",
  "winapi",
 ]
 
@@ -3377,6 +3795,12 @@ dependencies = [
  "web-sys",
 ]
 
+[[package]]
+name = "wildmatch"
+version = "2.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "939e59c1bc731542357fdaad98b209ef78c8743d652bb61439d16b16a79eb025"
+
 [[package]]
 name = "winapi"
 version = "0.3.9"
diff --git a/Cargo.toml b/Cargo.toml
index 6819fa72c7..841b5ac440 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -42,6 +42,7 @@ chrono = { version = "0.4.38", default-features = false, features = [
 config = { version = "0.13.4", default-features = false, features = ["toml"] }
 criterion = "0.5.1"
 crossterm = { version = "0.27", default-features = false }
+diffedit3 = "0.2.0"
 digest = "0.10.7"
 dirs = "5.0.1"
 either = "1.11.0"
diff --git a/cli/Cargo.toml b/cli/Cargo.toml
index 8d2b41c514..61febba541 100644
--- a/cli/Cargo.toml
+++ b/cli/Cargo.toml
@@ -46,6 +46,7 @@ name = "runner"
 cargo_metadata = { workspace = true }
 
 [dependencies]
+diffedit3 = { workspace = true }
 chrono = { workspace = true }
 clap = { workspace = true }
 clap-markdown = { workspace = true }
diff --git a/cli/src/merge_tools/builtin.rs b/cli/src/merge_tools/builtin.rs
index 673fc7e0fe..9719147ea1 100644
--- a/cli/src/merge_tools/builtin.rs
+++ b/cli/src/merge_tools/builtin.rs
@@ -17,6 +17,8 @@ use jj_lib::store::Store;
 use pollster::FutureExt;
 use thiserror::Error;
 
+// TODO(ilyagr): Rename this file and types to use BuiltinTUI instead of
+// Builtin, for symmetry with BuiltinWeb
 #[derive(Debug, Error)]
 pub enum BuiltinToolError {
     #[error("Failed to record changes")]
diff --git a/cli/src/merge_tools/builtin_web.rs b/cli/src/merge_tools/builtin_web.rs
new file mode 100644
index 0000000000..67b5e4d339
--- /dev/null
+++ b/cli/src/merge_tools/builtin_web.rs
@@ -0,0 +1,61 @@
+use std::sync::Arc;
+
+use jj_lib::backend::MergedTreeId;
+use jj_lib::gitignore::GitIgnoreFile;
+use jj_lib::matchers::Matcher;
+use jj_lib::merged_tree::MergedTree;
+
+use super::diff_working_copies::{DiffEditWorkingCopies, DiffSide};
+use super::DiffEditError;
+
+pub fn edit_diff_web(
+    left_tree: &MergedTree,
+    right_tree: &MergedTree,
+    matcher: &dyn Matcher,
+    instructions: Option<&str>,
+    base_ignores: Arc<GitIgnoreFile>,
+) -> Result<MergedTreeId, DiffEditError> {
+    let store = left_tree.store();
+    let diffedit_wc = DiffEditWorkingCopies::check_out(
+        store,
+        left_tree,
+        right_tree,
+        matcher,
+        Some(DiffSide::Right),
+        instructions,
+    )?;
+
+    // TODO(ilyagr): We may want to keep the files in-memory for the internal diff
+    // editor instead of treating the internal editor like an external tool. The
+    // main (minor) difficulty is to extract the functions to render and load
+    // conflicted files.
+    let diffedit_input = diffedit3::ThreeDirInput {
+        left: diffedit_wc
+            .working_copies
+            .left_working_copy_path()
+            .to_path_buf(),
+        right: diffedit_wc
+            .working_copies
+            .right_working_copy_path()
+            .to_path_buf(),
+        edit: diffedit_wc
+            .working_copies
+            .output_working_copy_path()
+            .unwrap()
+            .to_path_buf(),
+    };
+    tracing::info!(?diffedit_input, "Starting the diffedit3 local server");
+    // 17376 is a verified random number, as in https://xkcd.com/221/ :). I am
+    // trying to avoid 8000 or 8080 in case those, more commonly used, port
+    // numbers are used for something else.
+    //
+    // TODO: allow changing the ports and whether to open the browser.
+    match diffedit3::local_server::run_server_sync(Box::new(diffedit_input), 17376, 17380, true) {
+        Ok(()) => {}
+        Err(e) => {
+            return Err(DiffEditError::InternalWebTool(Box::new(e)));
+        }
+    };
+
+    diffedit_wc.snapshot_results(base_ignores)
+}
diff --git a/cli/src/merge_tools/mod.rs b/cli/src/merge_tools/mod.rs
index 8a45fa7a33..319c2d65e2 100644
--- a/cli/src/merge_tools/mod.rs
+++ b/cli/src/merge_tools/mod.rs
@@ -1,4 +1,4 @@
-// Copyright 2020 The Jujutsu Authors
+// Copyright 2024 The Jujutsu Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 mod builtin;
+mod builtin_web;
 mod diff_working_copies;
 mod external;
 
@@ -31,18 +32,19 @@ use pollster::FutureExt;
 use thiserror::Error;
 
 use self::builtin::{edit_diff_builtin, edit_merge_builtin, BuiltinToolError};
+use self::builtin_web::edit_diff_web;
 use self::diff_working_copies::DiffCheckoutError;
 use self::external::{edit_diff_external, ExternalToolError};
 pub use self::external::{generate_diff, ExternalMergeTool};
 use crate::config::CommandNameAndArgs;
 use crate::ui::Ui;
 
-const BUILTIN_EDITOR_NAME: &str = ":builtin";
-
 #[derive(Debug, Error)]
 pub enum DiffEditError {
     #[error(transparent)]
-    InternalTool(#[from] Box<BuiltinToolError>),
+    InternalTUITool(#[from] Box<BuiltinToolError>),
+    #[error(transparent)]
+    InternalWebTool(#[from] Box<diffedit3::local_server::MergeToolError>),
     #[error(transparent)]
     ExternalTool(#[from] ExternalToolError),
     #[error(transparent)]
@@ -65,6 +67,8 @@ pub enum DiffGenerateError {
 pub enum ConflictResolveError {
     #[error(transparent)]
     InternalTool(#[from] Box<BuiltinToolError>),
+    #[error("The ':builtin-web' tool cannot yet be used to resolve merge conflicts.")]
+    BuiltinWebNotImplemented,
     #[error(transparent)]
     ExternalTool(#[from] ExternalToolError),
     #[error("Couldn't find the path {0:?} in this revision")]
@@ -97,7 +101,8 @@ pub enum MergeToolConfigError {
 
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum MergeTool {
-    Builtin,
+    BuiltinTUI,
+    BuiltinWeb,
     // Boxed because ExternalMergeTool is big compared to the Builtin variant.
     External(Box<ExternalMergeTool>),
 }
@@ -119,7 +124,7 @@ fn editor_args_from_settings(
     if let Some(args) = settings.config().get(key).optional()? {
         Ok(args)
     } else {
-        let default_editor = BUILTIN_EDITOR_NAME;
+        let default_editor = ":builtin-tui";
         if let Some(mut writer) = ui.hint_default() {
             writeln!(
                 writer,
@@ -135,8 +140,10 @@ fn editor_args_from_settings(
 /// Resolves builtin merge tool name or loads external tool options from
 /// `[merge-tools.<name>]`.
 fn get_tool_config(settings: &UserSettings, name: &str) -> Result<Option<MergeTool>, ConfigError> {
-    if name == BUILTIN_EDITOR_NAME {
-        Ok(Some(MergeTool::Builtin))
+    if [":builtin", ":builtin-tui"].contains(&name) {
+        Ok(Some(MergeTool::BuiltinTUI))
+    } else if name == ":builtin-web" {
+        Ok(Some(MergeTool::BuiltinWeb))
     } else {
         Ok(get_external_tool_config(settings, name)?.map(MergeTool::external))
     }
@@ -222,21 +229,26 @@ impl DiffEditor {
         matcher: &dyn Matcher,
         instructions: Option<&str>,
     ) -> Result<MergedTreeId, DiffEditError> {
+        let instructions = self.use_instructions.then_some(instructions).flatten();
         match &self.tool {
-            MergeTool::Builtin => {
+            MergeTool::BuiltinTUI => {
                 Ok(edit_diff_builtin(left_tree, right_tree, matcher).map_err(Box::new)?)
             }
-            MergeTool::External(editor) => {
-                let instructions = self.use_instructions.then_some(instructions).flatten();
-                edit_diff_external(
-                    editor,
-                    left_tree,
-                    right_tree,
-                    matcher,
-                    instructions,
-                    self.base_ignores.clone(),
-                )
-            }
+            MergeTool::BuiltinWeb => edit_diff_web(
+                left_tree,
+                right_tree,
+                matcher,
+                instructions,
+                self.base_ignores.clone(),
+            ),
+            MergeTool::External(editor) => edit_diff_external(
+                editor,
+                left_tree,
+                right_tree,
+                matcher,
+                instructions,
+                self.base_ignores.clone(),
+            ),
         }
     }
 }
@@ -308,10 +320,11 @@ impl MergeEditor {
         let content = extract_as_single_hunk(&file_merge, tree.store(), repo_path).block_on();
 
         match &self.tool {
-            MergeTool::Builtin => {
+            MergeTool::BuiltinTUI => {
                 let tree_id = edit_merge_builtin(tree, repo_path, content).map_err(Box::new)?;
                 Ok(tree_id)
             }
+            MergeTool::BuiltinWeb => Err(ConflictResolveError::BuiltinWebNotImplemented),
             MergeTool::External(editor) => external::run_mergetool_external(
                 editor, file_merge, content, repo_path, conflict, tree,
             ),
@@ -340,7 +353,7 @@ mod tests {
             DiffEditor::with_name(name, &settings, GitIgnoreFile::empty()).map(|editor| editor.tool)
         };
 
-        insta::assert_debug_snapshot!(get(":builtin", "").unwrap(), @"Builtin");
+        insta::assert_debug_snapshot!(get(":builtin", "").unwrap(), @"BuiltinTUI");
 
         // Just program name, edit_args are filled by default
         insta::assert_debug_snapshot!(get("my diff", "").unwrap(), @r###"
@@ -399,7 +412,7 @@ mod tests {
         };
 
         // Default
-        insta::assert_debug_snapshot!(get("").unwrap(), @"Builtin");
+        insta::assert_debug_snapshot!(get("").unwrap(), @"BuiltinTUI");
 
         // Just program name, edit_args are filled by default
         insta::assert_debug_snapshot!(get(r#"ui.diff-editor = "my-diff""#).unwrap(), @r###"
@@ -546,7 +559,7 @@ mod tests {
             MergeEditor::with_name(name, &settings).map(|editor| editor.tool)
         };
 
-        insta::assert_debug_snapshot!(get(":builtin", "").unwrap(), @"Builtin");
+        insta::assert_debug_snapshot!(get(":builtin", "").unwrap(), @"BuiltinTUI");
 
         // Just program name
         insta::assert_debug_snapshot!(get("my diff", "").unwrap_err(), @r###"
@@ -595,7 +608,7 @@ mod tests {
         };
 
         // Default
-        insta::assert_debug_snapshot!(get("").unwrap(), @"Builtin");
+        insta::assert_debug_snapshot!(get("").unwrap(), @"BuiltinTUI");
 
         // Just program name
         insta::assert_debug_snapshot!(get(r#"ui.merge-editor = "my-merge""#).unwrap_err(), @r###"
diff --git a/cli/tests/test_resolve_command.rs b/cli/tests/test_resolve_command.rs
index d5f79f693c..7960308ad0 100644
--- a/cli/tests/test_resolve_command.rs
+++ b/cli/tests/test_resolve_command.rs
@@ -478,7 +478,7 @@ fn test_too_many_parents() {
 
     let error = test_env.jj_cmd_failure(&repo_path, &["resolve"]);
     insta::assert_snapshot!(error, @r###"
-    Hint: Using default editor ':builtin'; run `jj config set --user ui.merge-editor :builtin` to disable this message.
+    Hint: Using default editor ':builtin-tui'; run `jj config set --user ui.merge-editor :builtin` to disable this message.
     Resolving conflicts in: file
     Error: Failed to resolve conflicts
     Caused by: The conflict at "file" has 3 sides. At most 2 sides are supported.
@@ -556,7 +556,7 @@ fn test_file_vs_dir() {
     "###);
     let error = test_env.jj_cmd_failure(&repo_path, &["resolve"]);
     insta::assert_snapshot!(error, @r###"
-    Hint: Using default editor ':builtin'; run `jj config set --user ui.merge-editor :builtin` to disable this message.
+    Hint: Using default editor ':builtin-tui'; run `jj config set --user ui.merge-editor :builtin` to disable this message.
     Resolving conflicts in: file
     Error: Failed to resolve conflicts
     Caused by: Only conflicts that involve normal files (not symlinks, not executable, etc.) are supported. Conflict summary for "file":
@@ -613,7 +613,7 @@ fn test_description_with_dir_and_deletion() {
     "###);
     let error = test_env.jj_cmd_failure(&repo_path, &["resolve"]);
     insta::assert_snapshot!(error, @r###"
-    Hint: Using default editor ':builtin'; run `jj config set --user ui.merge-editor :builtin` to disable this message.
+    Hint: Using default editor ':builtin-tui'; run `jj config set --user ui.merge-editor :builtin` to disable this message.
     Resolving conflicts in: file
     Error: Failed to resolve conflicts
     Caused by: Only conflicts that involve normal files (not symlinks, not executable, etc.) are supported. Conflict summary for "file":
diff --git a/docs/config.md b/docs/config.md
index ec27c07e3b..f85800ec2a 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -448,13 +448,29 @@ Obviously, you would only set one line, don't copy them all in!
 ## Editing diffs
 
 The `ui.diff-editor` setting affects the tool used for editing diffs (e.g.  `jj
-split`, `jj squash -i`). The default is the special value `:builtin`, which
-launches a built-in TUI tool (known as [scm-diff-editor]) to edit the diff in
-your terminal.
+split`, `jj squash -i`).
+
+### Built-in diff editors
+
+The default is the special value `:builtin`, which is equivlaent to
+`:builtin-tui`. Either of these launches a built-in TUI tool
+(known as [scm-diff-editor]) to edit the diff in your terminal.
+
+There is also a built-in `:builtin-web` GUI editor (also knows as [diffedit3])
+that runs as a local server that is accessed with a web browser. The interface
+is similar to, and less poished than, that of the [`meld-3` Meld
+config](#experimental-3-pane-diff-editing), but requires neither installing Meld
+nor running Meld. `:builtin-web` can also be run over SSH with port forwarding.
+
+<!-- TODO(ilyagr): Explain what port it runs on, give example SSG commands -->
 
 [scm-diff-editor]: https://github.com/arxanas/scm-record?tab=readme-ov-file#scm-diff-editor
+[diffedit3]: https://github.com/ilyagr/diffedit3
 
-`jj` makes the following substitutions:
+### External diff editors
+
+`ui.diff-editor` can also be set to a command, or to a list of a command
+followed by its arguments. `jj` makes the following substitutions:
 
 - `$left` and `$right` are replaced with the paths to the left and right
   directories to diff respectively.