diff --git a/AGENTS.md b/AGENTS.md
index 6939d146b0..1b5e005130 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -130,7 +130,7 @@ When UI or text output changes intentionally, update the snapshots as follows:
 
 If you don’t have the tool:
 
-- `cargo install cargo-insta`
+- `cargo install --locked cargo-insta`
 
 ### Test assertions
 
diff --git a/docs/install.md b/docs/install.md
index b7d4f0711a..0991e7d16c 100644
--- a/docs/install.md
+++ b/docs/install.md
@@ -25,7 +25,7 @@ source "$HOME/.cargo/env"
 rustup component add rustfmt
 rustup component add clippy
 # Install helper tools used by the workspace justfile:
-cargo install just
+cargo install --locked just
 # Optional: install nextest for the `just test` helper
 cargo install --locked cargo-nextest
 
diff --git a/justfile b/justfile
index ca74c2e5c6..71eed89a35 100644
--- a/justfile
+++ b/justfile
@@ -47,7 +47,7 @@ install:
 # Run `cargo nextest` since it's faster than `cargo test`, though including
 # --no-fail-fast is important to ensure all tests are run.
 #
-# Run `cargo install cargo-nextest` if you don't have it installed.
+# Run `cargo install --locked cargo-nextest` if you don't have it installed.
 # Prefer this for routine local runs. Workspace crate features are banned, so
 # there should be no need to add `--all-features`.
 test:
diff --git a/tools/argument-comment-lint/README.md b/tools/argument-comment-lint/README.md
index 1b4895e325..7270c48867 100644
--- a/tools/argument-comment-lint/README.md
+++ b/tools/argument-comment-lint/README.md
@@ -54,7 +54,7 @@ create_openai_url(None, 3);
 Install the required tooling once:
 
 ```bash
-cargo install cargo-dylint dylint-link
+cargo install --locked cargo-dylint dylint-link
 rustup toolchain install nightly-2025-09-18 \
   --component llvm-tools-preview \
   --component rustc-dev \