diff --git a/.bazelignore b/.bazelignore
new file mode 100644
index 0000000..92b2793
--- /dev/null
+++ b/.bazelignore
@@ -0,0 +1 @@
+.direnv
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d343d84..10bec8e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -5,7 +5,6 @@
 Requires [Nix](https://nixos.org/) with flakes enabled.
 
 ```bash
-# enter dev shell
 direnv allow   # or: nix develop
 ```
 
@@ -15,29 +14,42 @@ direnv allow   # or: nix develop
 cargo build --workspace
 cargo test --workspace
 cargo clippy --workspace -- -D warnings
+cargo fmt --check
 ```
 
 ## Bazel
 
 ```bash
 build   # alias: bazel build //...
-test    # alias: bazel test //...
+check   # alias: bazel test //...
 ```
 
-## Format
+## Parity tests
+
+Every module must produce identical results across all bindings. The `tests/parity/` suite generates a `golden.json` from `stdbr-core` and validates Rust, Node.js, Python, FFI-C, and WASM against it.
 
 ```bash
-fmt     # alias: nix fmt
+bazel test //tests/parity/...
 ```
 
-## Building specific bindings
+When adding a new function to core, add the corresponding test cases to `tools/parity_gen/src/main.rs` and update every `test_parity.*` file.
 
-```bash
-cargo build -p stdbr-python
-cargo build -p stdbr-wasm --target wasm32-unknown-unknown
-cd bindings/python && maturin develop
-cd bindings/wasm && wasm-pack build --target web
-```
+## Adding a new binding target
+
+1. Create `bindings/<target>/` with `Cargo.toml` and source
+2. Expose the same API surface as existing bindings (parse, validate, format, generate)
+3. Add `test_parity.*` that reads `golden.json` and validates all cases
+4. Add build + test rules in `tests/parity/BUILD.bazel`
+5. Register the Cargo manifest in `MODULE.bazel`
+
+## Adding a new BR module
+
+1. Implement in `core/src/<module>.rs` (`no_std` + `alloc`)
+2. Export from `core/src/lib.rs`
+3. Add bindings in all targets: `ffi-c`, `nodejs`, `python`, `wasm`
+4. Add golden test cases in `tools/parity_gen/src/main.rs`
+5. Update all `test_parity.*` files to cover the new module
+6. If the module needs external data (like municipio uses IBGE), add a sync workflow in `.github/workflows/`
 
 ## Project structure
 
@@ -45,12 +57,15 @@ cd bindings/wasm && wasm-pack build --target web
 stdbr/
   core/                    # stdbr-core (no_std Rust library)
   bindings/
-    ffi-c/                 # C/C++ FFI (cdylib + staticlib + cbindgen)
+    ffi-c/                 # C/C++ FFI (staticlib + cbindgen)
     nodejs/                # Node.js via napi-rs
     python/                # Python via PyO3 + maturin
     wasm/                  # WebAssembly via wasm-bindgen
-  tools/                   # Bazel custom rules
-  .github/workflows/       # CI (Nix-based)
+  tools/
+    parity_gen/            # Golden test data generator
+    rules_rust_extras/     # Bazel custom rules (cbindgen)
+  tests/parity/            # Cross-binding parity tests
+  .github/workflows/       # CI + IBGE sync
   flake.nix                # Nix dev environment
   MODULE.bazel             # Bazel module config
 ```
diff --git a/README.md b/README.md
index eda2eba..2c9a453 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 [![CI](https://github.com/fullzer4/stdbr/actions/workflows/ci.yml/badge.svg)](https://github.com/fullzer4/stdbr/actions/workflows/ci.yml)
 [![IBGE Sync](https://github.com/fullzer4/stdbr/actions/workflows/ibge-sync.yml/badge.svg)](https://github.com/fullzer4/stdbr/actions/workflows/ibge-sync.yml)
-[![License: Apache-2.0](https://img.shields.io/badge/license-MIT%20OR%20Apache--2.0-blue.svg)](LICENSE)
+[![License: Apache-2.0](https://img.shields.io/badge/license-Apache--2.0-blue.svg)](LICENSE)
 
 Standard library for Brazil.
 
diff --git a/flake.nix b/flake.nix
index 0afdc33..095f11d 100644
--- a/flake.nix
+++ b/flake.nix
@@ -96,7 +96,7 @@
                 category = "bazel";
               }
               {
-                name = "test";
+                name = "check";
                 command = "bazel test //...";
                 help = "Run all tests";
                 category = "bazel";