diff --git a/Cargo.lock b/Cargo.lock
index 93e6fcd5..aa72fe2b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -102,6 +102,15 @@ dependencies = [
  "alloc-no-stdlib",
 ]
 
+[[package]]
+name = "alloca"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5a7d05ea6aea7e9e64d25b9156ba2fee3fdd659e34e41063cd2fc7cd020d7f4"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "allsorts-azul"
 version = "0.17.2"
@@ -134,6 +143,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "anes"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4b46cbb362ab8752921c97e041f5e366ee6297bd428a31275b9fcf1e380f7299"
+
 [[package]]
 name = "anstream"
 version = "1.0.0"
@@ -731,6 +746,12 @@ dependencies = [
  "zip 8.6.0",
 ]
 
+[[package]]
+name = "cast"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37b2a672a2cb129a2e41c10b1224bb368f9f37a2b16b612598138befd7b37eb5"
+
 [[package]]
 name = "cbc"
 version = "0.2.1"
@@ -794,6 +815,33 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6e4de3bc4ea267985becf712dc6d9eed8b04c953b3fcfb339ebc87acd9804901"
 
+[[package]]
+name = "ciborium"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "42e69ffd6f0917f5c029256a24d0161db17cea3997d185db0d35926308770f0e"
+dependencies = [
+ "ciborium-io",
+ "ciborium-ll",
+ "serde",
+]
+
+[[package]]
+name = "ciborium-io"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "05afea1e0a06c9be33d539b876f1ce3692f4afea2cb41f740e7743225ed1c757"
+
+[[package]]
+name = "ciborium-ll"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "57663b653d948a338bfb3eeba9bb2fd5fcfaecb9e199e87e1eda4d9e8b240fd9"
+dependencies = [
+ "ciborium-io",
+ "half",
+]
+
 [[package]]
 name = "cipher"
 version = "0.4.4"
@@ -999,6 +1047,41 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "criterion"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "950046b2aa2492f9a536f5f4f9a3de7b9e2476e575e05bd6c333371add4d98f3"
+dependencies = [
+ "alloca",
+ "anes",
+ "cast",
+ "ciborium",
+ "clap",
+ "criterion-plot",
+ "itertools 0.13.0",
+ "num-traits",
+ "oorandom",
+ "page_size",
+ "plotters",
+ "rayon",
+ "regex",
+ "serde",
+ "serde_json",
+ "tinytemplate",
+ "walkdir",
+]
+
+[[package]]
+name = "criterion-plot"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d8d80a2f4f5b554395e47b5d8305bc3d27813bacb73493eb1001e8f76dae29ea"
+dependencies = [
+ "cast",
+ "itertools 0.13.0",
+]
+
 [[package]]
 name = "crossbeam-deque"
 version = "0.8.7"
@@ -1956,6 +2039,15 @@ version = "1.70.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a6cb138bb79a146c1bd460005623e142ef0181e3d0219cb493e02f7d08a35695"
 
+[[package]]
+name = "itertools"
+version = "0.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "413ee7dfc52ee1a4949ceeb7dbc8a33f2d6c088194d9f922fb8318faf1f01186"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itertools"
 version = "0.14.0"
@@ -2476,6 +2568,12 @@ version = "1.70.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "384b8ab6d37215f3c5301a95a4accb5d64aa607f1fcb26a11b5303878451b4fe"
 
+[[package]]
+name = "oorandom"
+version = "11.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d6790f58c7ff633d8771f42965289203411a5e5c68388703c06e14f24770b41e"
+
 [[package]]
 name = "option-ext"
 version = "0.2.0"
@@ -2516,6 +2614,16 @@ dependencies = [
  "syn 2.0.119",
 ]
 
+[[package]]
+name = "page_size"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "30d5b2194ed13191c1999ae0704b7839fb18384fa22e49b57eeaa97d79ce40da"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
 [[package]]
 name = "parking"
 version = "2.2.1"
@@ -2658,6 +2766,34 @@ version = "0.3.34"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f6b464fbc74e149a392436b17d523f769e057cb6877f6a5c4618bc6f11800548"
 
+[[package]]
+name = "plotters"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5aeb6f403d7a4911efb1e33402027fc44f29b5bf6def3effcc22d7bb75f2b747"
+dependencies = [
+ "num-traits",
+ "plotters-backend",
+ "plotters-svg",
+ "wasm-bindgen",
+ "web-sys",
+]
+
+[[package]]
+name = "plotters-backend"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "df42e13c12958a16b3f7f4386b9ab1f3e7933914ecea48da7139435263a4172a"
+
+[[package]]
+name = "plotters-svg"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "51bae2ac328883f7acdfea3d66a7c35751187f870bc81f94563733a154d7a670"
+dependencies = [
+ "plotters-backend",
+]
+
 [[package]]
 name = "png"
 version = "0.18.1"
@@ -3000,7 +3136,7 @@ dependencies = [
  "built",
  "cfg-if",
  "interpolate_name",
- "itertools",
+ "itertools 0.14.0",
  "libc",
  "libfuzzer-sys",
  "log",
@@ -3089,6 +3225,18 @@ dependencies = [
  "thiserror",
 ]
 
+[[package]]
+name = "regex"
+version = "1.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f020237b6c8eed93db2e2cb53c00c60a8e1bc73da7d073199a1180401450218d"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
 [[package]]
 name = "regex-automata"
 version = "0.4.18"
@@ -3275,6 +3423,15 @@ version = "1.0.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9774ba4a74de5f7b1c1451ed6cd5285a32eddb5cccb8cc655a4e50009e06477f"
 
+[[package]]
+name = "same-file"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "93fc1dc3aaa9bfed95e02e6eadabb4baf7e3078b0bd1b4d7b6b0b68378900502"
+dependencies = [
+ "winapi-util",
+]
+
 [[package]]
 name = "scopeguard"
 version = "1.2.0"
@@ -3771,6 +3928,7 @@ dependencies = [
 name = "techscript_lsp"
 version = "2.0.0"
 dependencies = [
+ "criterion",
  "serde",
  "serde_json",
  "techscript_ast",
@@ -4038,6 +4196,16 @@ dependencies = [
  "zerovec",
 ]
 
+[[package]]
+name = "tinytemplate"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "be4d6b5f19ff7664e8c98d03e2139cb510db9b0a60b55f8e8709b689d939b6bc"
+dependencies = [
+ "serde",
+ "serde_json",
+]
+
 [[package]]
 name = "tinyvec"
 version = "1.12.0"
@@ -4426,6 +4594,16 @@ version = "0.9.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 
+[[package]]
+name = "walkdir"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29790946404f91d9c5d06f9874efddea1dc06c5efe94541a7d6863108e3a5e4b"
+dependencies = [
+ "same-file",
+ "winapi-util",
+]
+
 [[package]]
 name = "wasi"
 version = "0.11.1+wasi-snapshot-preview1"
@@ -4496,6 +4674,16 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "web-sys"
+version = "0.3.104"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c435338968042f4f59a557f690a253676d47ce13ceb55d70100e7facf6620a30"
+dependencies = [
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "webpki-roots"
 version = "0.26.11"
@@ -4542,6 +4730,15 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
 
+[[package]]
+name = "winapi-util"
+version = "0.1.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c2a7b1c03c876122aa43f3020e6c3c3ee5c05081c9a00739faf7503aeba10d22"
+dependencies = [
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "winapi-x86_64-pc-windows-gnu"
 version = "0.4.0"
diff --git a/tools/lsp/Cargo.toml b/tools/lsp/Cargo.toml
index dfe0d447..9c857efc 100644
--- a/tools/lsp/Cargo.toml
+++ b/tools/lsp/Cargo.toml
@@ -20,3 +20,10 @@ tower-lsp = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 tokio = { version = "1", features = ["full"] }
+
+[dev-dependencies]
+criterion = "0.8.2"
+
+[[bench]]
+name = "bench"
+harness = false
diff --git a/tools/lsp/benches/bench.rs b/tools/lsp/benches/bench.rs
new file mode 100644
index 00000000..bac9cdd1
--- /dev/null
+++ b/tools/lsp/benches/bench.rs
@@ -0,0 +1,64 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+
+fn find_boundary_slow(line: &str, word: &str) -> usize {
+    let mut count = 0;
+    let word_len = word.len();
+    let mut start_pos = 0;
+    while let Some(pos_in_line) = line[start_pos..].find(word) {
+        let actual_pos = start_pos + pos_in_line;
+        let char_before = if actual_pos > 0 {
+            line.chars().nth(actual_pos - 1)
+        } else {
+            None
+        };
+        let char_after = line.chars().nth(actual_pos + word_len);
+
+        let is_boundary_before = char_before.is_none_or(|c| !c.is_alphanumeric() && c != '_');
+        let is_boundary_after = char_after.is_none_or(|c| !c.is_alphanumeric() && c != '_');
+
+        if is_boundary_before && is_boundary_after {
+            count += 1;
+        }
+        start_pos = actual_pos + word_len;
+    }
+    count
+}
+
+fn find_boundary_fast(line: &str, word: &str) -> usize {
+    let mut count = 0;
+    let word_len = word.len();
+    let mut start_pos = 0;
+    while let Some(pos_in_line) = line[start_pos..].find(word) {
+        let actual_pos = start_pos + pos_in_line;
+        let char_before = if actual_pos > 0 {
+            line[..actual_pos].chars().next_back()
+        } else {
+            None
+        };
+        let char_after = line[actual_pos + word_len..].chars().next();
+
+        let is_boundary_before = char_before.is_none_or(|c| !c.is_alphanumeric() && c != '_');
+        let is_boundary_after = char_after.is_none_or(|c| !c.is_alphanumeric() && c != '_');
+
+        if is_boundary_before && is_boundary_after {
+            count += 1;
+        }
+        start_pos = actual_pos + word_len;
+    }
+    count
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let long_line = "let abc = 123; ".repeat(1000);
+    let word = "abc";
+
+    c.bench_function("slow", |b| {
+        b.iter(|| find_boundary_slow(std::hint::black_box(&long_line), std::hint::black_box(word)))
+    });
+    c.bench_function("fast", |b| {
+        b.iter(|| find_boundary_fast(std::hint::black_box(&long_line), std::hint::black_box(word)))
+    });
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);
diff --git a/tools/lsp/src/lib.rs b/tools/lsp/src/lib.rs
index 7ef4fad8..15caf177 100644
--- a/tools/lsp/src/lib.rs
+++ b/tools/lsp/src/lib.rs
@@ -752,11 +752,11 @@ impl LanguageServer for Backend {
             while let Some(pos_in_line) = line[start_pos..].find(&word) {
                 let actual_pos = start_pos + pos_in_line;
                 let char_before = if actual_pos > 0 {
-                    line.chars().nth(actual_pos - 1)
+                    line[..actual_pos].chars().next_back()
                 } else {
                     None
                 };
-                let char_after = line.chars().nth(actual_pos + word_len);
+                let char_after = line[actual_pos + word_len..].chars().next();
 
                 let is_boundary_before =
                     char_before.map_or(true, |c| !c.is_alphanumeric() && c != '_');
@@ -803,11 +803,11 @@ impl LanguageServer for Backend {
             while let Some(pos_in_line) = line[start_pos..].find(&word) {
                 let actual_pos = start_pos + pos_in_line;
                 let char_before = if actual_pos > 0 {
-                    line.chars().nth(actual_pos - 1)
+                    line[..actual_pos].chars().next_back()
                 } else {
                     None
                 };
-                let char_after = line.chars().nth(actual_pos + word_len);
+                let char_after = line[actual_pos + word_len..].chars().next();
 
                 let is_boundary_before =
                     char_before.map_or(true, |c| !c.is_alphanumeric() && c != '_');