diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index dfa28c9f0..f34ce2764 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -13,6 +13,14 @@ cargo test --workspace
 cargo xtask ci                           # what every commit must pass
 ```
 
+The default `dev` profile keeps debug info to line tables: builds are fast and panics/backtraces
+still name the file and line, but a debugger cannot show local variables. For an interactive
+debugger session use the `dev-full` profile, which is the same build with full debug info:
+
+```sh
+cargo run --profile dev-full -p effectcraft -- --demo
+```
+
 ## Ground rules
 
 - **Clean room.** Work from After Effects' public documentation and its observable behaviour only.
diff --git a/Cargo.toml b/Cargo.toml
index aa917fc63..dee46306d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -153,6 +153,13 @@ opt-level = 1
 # Panics and backtraces keep file and line; full debug info only made the many test binaries large.
 debug = "line-tables-only"
 
+# Same settings as `dev`, but with full debug info for interactive debugger sessions: local
+# variables, parameters and column breakpoints work. Use `--profile dev-full` when debugging;
+# everything else stays on the fast default. See CONTRIBUTING.md, "Setup".
+[profile.dev-full]
+inherits = "dev"
+debug = true
+
 # Pixel hot loops: keep debug builds interactive.
 [profile.dev.package.effectcraft-raster]
 opt-level = 3
diff --git a/docs/testing.md b/docs/testing.md
index 67d622fd9..d556fdc4f 100644
--- a/docs/testing.md
+++ b/docs/testing.md
@@ -5,6 +5,10 @@ cargo test --workspace     # everything
 cargo xtask ci             # fmt, clippy -D warnings, tests, layers, assets, wasm
 ```
 
+The `dev` profile keeps debug info to line tables (fast builds, readable backtraces). To debug
+interactively — local variables, parameters, column breakpoints — build with the `dev-full`
+profile: `cargo run --profile dev-full -p effectcraft -- --demo` (see `CONTRIBUTING.md`).
+
 `cargo xtask ci` builds in the dev profile and runs the tests with `cargo nextest run` (plus
 `cargo test --doc`) when `cargo-nextest` is installed, and with `cargo test` otherwise. It then
 runs `missing_translations_report` with `--nocapture`, which prints the interface strings each