diff --git a/.gitignore b/.gitignore
index 9872b4fd2..d82845757 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,15 +3,18 @@
 *\#
 *~
 .*.swp
-.DS_Store
 .build
 .coverage
+.DS_Store
 .mypy_cache
 .pytype
 __pycache__
 anki/buildhash.py
+anki/proto
 aqt/forms
 locale
+rs/ankirs/src/proto.rs
+rs/target
 tools/runanki.system
 ts/node_modules
 web/deckbrowser.js
@@ -20,4 +23,3 @@ web/overview.js
 web/reviewer-bottom.js
 web/reviewer.js
 web/webview.js
-rs/target
diff --git a/Makefile b/Makefile
index 4870cc295..ed9edf687 100644
--- a/Makefile
+++ b/Makefile
@@ -96,6 +96,11 @@ RUST_TOOLCHAIN := $(shell cat rs/rust-toolchain)
 	rustup component add clippy-preview --toolchain $(RUST_TOOLCHAIN)
 	@touch $@
 
+# Protobuf
+######################
+
+PROTODEPS := $(wildcard proto/*.proto)
+
 # Typescript source
 ######################
 
@@ -105,12 +110,12 @@ JSDEPS := $(patsubst ts/src/%.ts, web/%.js, $(TSDEPS))
 # Rust source
 ######################
 
-RSDEPS := $(wildcard rs/*/src/*.rs)
+RSDEPS := $(shell find rs -type f | grep -v target)
 
 # Building
 ######################
 
-BUILDDEPS := .build/ui .build/js .build/rs
+BUILDDEPS := .build/ui .build/js .build/rs .build/py-proto
 
 .build/ui: $(RUNREQS) $(shell find designer -type f)
 	./tools/build_ui.sh
@@ -120,10 +125,14 @@ BUILDDEPS := .build/ui .build/js .build/rs
 	(cd ts && npm run build)
 	@touch $@
 
-.build/rs: .build/rust-deps $(RUNREQS) $(RSDEPS)
+.build/rs: .build/rust-deps $(RUNREQS) $(RSDEPS) $(PROTODEPS)
 	(cd rs/pybridge && maturin develop $(RUSTARGS))
 	@touch $@
 
+.build/py-proto: $(RUNREQS) $(PROTODEPS)
+	protoc -I proto --python_betterproto_out=anki/proto proto/bridge.proto
+	@touch $@
+
 .PHONY: build clean
 
 build: $(BUILDDEPS)
@@ -147,6 +156,9 @@ run: build
 .PHONY: check
 check: rs-test rs-fmt rs-clippy py-mypy py-test py-fmt py-imports py-lint ts-fmt
 
+.PHONY: fix
+fix: fix-py-fmt fix-py-imports fix-rs-fmt fix-ts-fmt
+
 # Checking python
 ######################
 
@@ -156,7 +168,7 @@ PYCHECKDEPS := $(BUILDDEPS) .build/py-check-reqs $(shell find anki aqt -name '*.
 	mypy anki aqt
 	@touch $@
 
-.build/pytest: $(PYCHECKDEPS) $(wildcard tests/*.py)
+.build/py-test: $(PYCHECKDEPS) $(wildcard tests/*.py)
 	./tools/tests.sh
 	@touch $@
 
diff --git a/anki/collection.py b/anki/collection.py
index 8eb74b15e..9c36362a8 100644
--- a/anki/collection.py
+++ b/anki/collection.py
@@ -29,6 +29,7 @@ from anki.lang import _, ngettext
 from anki.media import MediaManager
 from anki.models import ModelManager
 from anki.notes import Note
+from anki.rsbridge import RSBridge
 from anki.sched import Scheduler as V1Scheduler
 from anki.schedv2 import Scheduler as V2Scheduler
 from anki.sound import stripSounds
@@ -84,8 +85,12 @@ class _Collection:
     ls: int
     conf: Dict[str, Any]
     _undo: List[Any]
+    rust: RSBridge
 
-    def __init__(self, db: DB, server: bool = False, log: bool = False) -> None:
+    def __init__(
+        self, db: DB, server: bool = False, log: bool = False, rust: RSBridge = None
+    ) -> None:
+        self.rust = rust
         self._debugLog = log
         self.db = db
         self.path = db._path
diff --git a/anki/rsbridge.py b/anki/rsbridge.py
index 9f0ac5e25..17132d528 100644
--- a/anki/rsbridge.py
+++ b/anki/rsbridge.py
@@ -1,10 +1,37 @@
 import _ankirs  # pytype: disable=import-error
+import betterproto
+
+from anki.proto import proto as pb
+
+
+class BridgeException(Exception):
+    def __str__(self) -> str:
+        err: pb.BridgeError = self.args[0]  # pylint: disable=unsubscriptable-object
+        (kind, obj) = betterproto.which_one_of(err, "value")
+        if kind == "invalid_input":
+            return f"invalid input: {obj.info}"
+        else:
+            return f"unhandled error: {err} {obj}"
 
 
 class RSBridge:
     def __init__(self):
         self._bridge = _ankirs.Bridge()
-        assert self._bridge.cmd("") == "test"
+
+    def _run_command(self, input: pb.BridgeInput) -> pb.BridgeOutput:
+        input_bytes = bytes(input)
+        output_bytes = self._bridge.command(input_bytes)
+        output = pb.BridgeOutput().parse(output_bytes)
+        (kind, obj) = betterproto.which_one_of(output, "value")
+        if kind == "error":
+            raise BridgeException(obj)
+        else:
+            return output
+
+    def plus_one(self, num: int) -> int:
+        input = pb.BridgeInput(plus_one=pb.PlusOneIn(num=num))
+        output = self._run_command(input)
+        return output.plus_one.num
 
 
 bridge = RSBridge()
diff --git a/anki/storage.py b/anki/storage.py
index 5855a1f95..b75a54827 100644
--- a/anki/storage.py
+++ b/anki/storage.py
@@ -12,6 +12,7 @@ from anki.collection import _Collection
 from anki.consts import *
 from anki.db import DB
 from anki.lang import _
+from anki.rsbridge import RSBridge
 from anki.stdmodels import (
     addBasicModel,
     addBasicTypingModel,
@@ -26,6 +27,8 @@ def Collection(
     path: str, lock: bool = True, server: bool = False, log: bool = False
 ) -> _Collection:
     "Open a new or existing collection. Path must be unicode."
+    bridge = RSBridge()
+    assert bridge.plus_one(5) == 6
     assert path.endswith(".anki2")
     path = os.path.abspath(path)
     create = not os.path.exists(path)
@@ -46,7 +49,7 @@ def Collection(
         db.execute("pragma journal_mode = wal")
     db.setAutocommit(False)
     # add db to col and do any remaining upgrades
-    col = _Collection(db, server, log)
+    col = _Collection(db, server, log, rust=bridge)
     if ver < SCHEMA_VERSION:
         _upgrade(col, ver)
     elif ver > SCHEMA_VERSION:
diff --git a/proto/bridge.proto b/proto/bridge.proto
new file mode 100644
index 000000000..a132e308b
--- /dev/null
+++ b/proto/bridge.proto
@@ -0,0 +1,36 @@
+syntax = "proto3";
+
+package proto;
+
+message Empty {}
+
+message BridgeInput {
+    oneof value {
+        PlusOneIn plus_one = 2;
+    }
+}
+
+message BridgeOutput {
+    oneof value {
+        BridgeError error = 1;
+        PlusOneOut plus_one = 2;
+    }
+}
+
+message BridgeError {
+    oneof value {
+        InvalidInputError invalid_input = 1;
+    }
+}
+
+message InvalidInputError {
+    string info = 1;
+}
+
+message PlusOneIn {
+    int32 num = 1;
+}
+
+message PlusOneOut {
+    int32 num = 1;
+}
diff --git a/requirements.txt b/requirements.txt
index 3dd8678ba..4788d0bb2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,3 +8,4 @@ jsonschema
 psutil; sys_platform == "win32"
 distro; sys_platform != "win32" and sys_platform != "darwin"
 typing
+betterproto[compiler]
diff --git a/rs/Cargo.lock b/rs/Cargo.lock
index a8ec493ff..d63b0c82b 100644
--- a/rs/Cargo.lock
+++ b/rs/Cargo.lock
@@ -12,6 +12,12 @@ dependencies = [
 [[package]]
 name = "ankirs"
 version = "0.1.0"
+dependencies = [
+ "bytes",
+ "failure",
+ "prost",
+ "prost-build",
+]
 
 [[package]]
 name = "autocfg"
@@ -19,14 +25,118 @@ version = "0.1.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1d49d90015b3c36167a20fe2810c5cd875ad504b39cff3d4eae7977e6b7c1cb2"
 
+[[package]]
+name = "backtrace"
+version = "0.3.40"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "924c76597f0d9ca25d762c25a4d369d51267536465dc5064bdf0eb073ed477ea"
+dependencies = [
+ "backtrace-sys",
+ "cfg-if",
+ "libc",
+ "rustc-demangle",
+]
+
+[[package]]
+name = "backtrace-sys"
+version = "0.1.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5d6575f128516de27e3ce99689419835fce9643a9b215a14d2b5b685be018491"
+dependencies = [
+ "cc",
+ "libc",
+]
+
+[[package]]
+name = "byteorder"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a7c3dd8985a7111efc5c80b44e23ecdd8c007de8ade3b96595387e812b957cf5"
+
+[[package]]
+name = "bytes"
+version = "0.4.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "206fdffcfa2df7cbe15601ef46c813fce0965eb3286db6b56c583b814b51c81c"
+dependencies = [
+ "byteorder",
+ "iovec",
+]
+
+[[package]]
+name = "c2-chacha"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "214238caa1bf3a496ec3392968969cab8549f96ff30652c9e56885329315f6bb"
+dependencies = [
+ "ppv-lite86",
+]
+
+[[package]]
+name = "cc"
+version = "1.0.48"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f52a465a666ca3d838ebbf08b241383421412fe7ebb463527bba275526d89f76"
+
+[[package]]
+name = "cfg-if"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
+
 [[package]]
 name = "ctor"
 version = "0.1.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cd8ce37ad4184ab2ce004c33bf6379185d3b1c95801cab51026bd271bf68eedc"
 dependencies = [
- "quote",
- "syn",
+ "quote 1.0.2",
+ "syn 1.0.11",
+]
+
+[[package]]
+name = "either"
+version = "1.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb1f6b1ce1c140482ea30ddd3335fc0024ac7ee112895426e0a629a6c20adfe3"
+
+[[package]]
+name = "failure"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8273f13c977665c5db7eb2b99ae520952fe5ac831ae4cd09d80c4c7042b5ed9"
+dependencies = [
+ "backtrace",
+ "failure_derive",
+]
+
+[[package]]
+name = "failure_derive"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0bc225b78e0391e4b8683440bf2e63c2deeeb2ce5189eab46e2b68c6d3725d08"
+dependencies = [
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
+ "synstructure",
+]
+
+[[package]]
+name = "fixedbitset"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "86d4de0081402f5e88cdac65c8dcdcc73118c1a7a465e2a05f0da05843a8ea33"
+
+[[package]]
+name = "getrandom"
+version = "0.1.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e7db7ca94ed4cd01190ceee0d8a8052f08a247aa1b469a7f68c6a3b71afcf407"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
 ]
 
 [[package]]
@@ -35,9 +145,18 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2a36606a68532b5640dc86bb1f33c64b45c4682aad4c50f3937b317ea387f3d6"
 dependencies = [
- "proc-macro2",
- "quote",
- "syn",
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
+]
+
+[[package]]
+name = "heck"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "20564e78d53d2bb135c343b3f47714a56af2061f1c928fdb541dc7b9fdd94205"
+dependencies = [
+ "unicode-segmentation",
 ]
 
 [[package]]
@@ -57,9 +176,9 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b714fc08d0961716390977cdff1536234415ac37b509e34e5a983def8340fb75"
 dependencies = [
  "proc-macro-hack",
- "proc-macro2",
- "quote",
- "syn",
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
  "unindent",
 ]
 
@@ -80,9 +199,27 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c2869bf972e998977b1cb87e60df70341d48e48dca0823f534feb91ea44adaf9"
 dependencies = [
- "proc-macro2",
- "quote",
- "syn",
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
+]
+
+[[package]]
+name = "iovec"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b2b3ea6ff95e175473f8ffe6a7eb7c00d054240321b84c57051175fe3c1e075e"
+dependencies = [
+ "libc",
+]
+
+[[package]]
+name = "itertools"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f56a2d0bc861f9165be4eb3442afd3c236d8a98afd426f65d92324ae1091a484"
+dependencies = [
+ "either",
 ]
 
 [[package]]
@@ -103,12 +240,27 @@ version = "0.2.66"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d515b1f41455adea1313a4a2ac8a8a477634fbae63cc6100e3aebb207ce61558"
 
+[[package]]
+name = "log"
+version = "0.4.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14b6052be84e6b71ab17edffc2eeabf5c2c3ae1fdb464aae35ac50c67a44e1f7"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "memchr"
 version = "2.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "88579771288728879b57485cc7d6b07d648c9f0141eb955f8ab7f9d45394468e"
 
+[[package]]
+name = "multimap"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2eb04b9f127583ed176e163fb9ec6f3e793b87e21deedd5734a69386a18a0151"
+
 [[package]]
 name = "num-traits"
 version = "0.2.10"
@@ -135,20 +287,44 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4214c9e912ef61bf42b81ba9a47e8aad1b2ffaf739ab162bf96d1e011f54e6c5"
 dependencies = [
  "proc-macro-hack",
- "proc-macro2",
- "quote",
- "syn",
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
 ]
 
+[[package]]
+name = "petgraph"
+version = "0.4.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c3659d1ee90221741f65dd128d9998311b0e40c5d3c23a62445938214abce4f"
+dependencies = [
+ "fixedbitset",
+]
+
+[[package]]
+name = "ppv-lite86"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "74490b50b9fbe561ac330df47c08f3f33073d2d00c150f719147d7c54522fa1b"
+
 [[package]]
 name = "proc-macro-hack"
 version = "0.5.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ecd45702f76d6d3c75a80564378ae228a85f0b59d2f3ed43c91b4a69eb2ebfc5"
 dependencies = [
- "proc-macro2",
- "quote",
- "syn",
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "0.4.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf3d2011ab5c909338f7887f4fc896d35932e29146c12c8d01da6b22a80ba759"
+dependencies = [
+ "unicode-xid 0.1.0",
 ]
 
 [[package]]
@@ -157,13 +333,66 @@ version = "1.0.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9c9e470a8dc4aeae2dee2f335e8f533e2d4b347e1434e5671afc49b054592f27"
 dependencies = [
- "unicode-xid",
+ "unicode-xid 0.2.0",
+]
+
+[[package]]
+name = "prost"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "96d14b1c185652833d24aaad41c5832b0be5616a590227c1fbff57c616754b23"
+dependencies = [
+ "byteorder",
+ "bytes",
+ "prost-derive",
+]
+
+[[package]]
+name = "prost-build"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eb788126ea840817128183f8f603dce02cb7aea25c2a0b764359d8e20010702e"
+dependencies = [
+ "bytes",
+ "heck",
+ "itertools",
+ "log",
+ "multimap",
+ "petgraph",
+ "prost",
+ "prost-types",
+ "tempfile",
+ "which",
+]
+
+[[package]]
+name = "prost-derive"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e7dc378b94ac374644181a2247cebf59a6ec1c88b49ac77f3a94b86b79d0e11"
+dependencies = [
+ "failure",
+ "itertools",
+ "proc-macro2 0.4.30",
+ "quote 0.6.13",
+ "syn 0.15.44",
+]
+
+[[package]]
+name = "prost-types"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1de482a366941c8d56d19b650fac09ca08508f2a696119ee7513ad590c8bac6f"
+dependencies = [
+ "bytes",
+ "prost",
 ]
 
 [[package]]
 name = "pybridge"
 version = "0.1.0"
 dependencies = [
+ "ankirs",
  "pyo3",
 ]
 
@@ -194,9 +423,9 @@ version = "0.8.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9f6e56fb3e97b344a8f87d036f94578399402c6b75949de6270cd07928f790b1"
 dependencies = [
- "proc-macro2",
- "quote",
- "syn",
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
 ]
 
 [[package]]
@@ -205,10 +434,19 @@ version = "0.8.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "97452dcdf5941627ebc5c06664a07821fc7fc88d7515f02178193a8ebe316468"
 dependencies = [
- "proc-macro2",
+ "proc-macro2 1.0.6",
  "pyo3-derive-backend",
- "quote",
- "syn",
+ "quote 1.0.2",
+ "syn 1.0.11",
+]
+
+[[package]]
+name = "quote"
+version = "0.6.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ce23b6b870e8f94f81fb0a363d65d86675884b34a09043c81e5562f11c1f8e1"
+dependencies = [
+ "proc-macro2 0.4.30",
 ]
 
 [[package]]
@@ -217,9 +455,56 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "053a8c8bcc71fcce321828dc897a98ab9760bef03a4fc36693c231e5b3216cfe"
 dependencies = [
- "proc-macro2",
+ "proc-macro2 1.0.6",
 ]
 
+[[package]]
+name = "rand"
+version = "0.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ae1b169243eaf61759b8475a998f0a385e42042370f3a7dbaf35246eacc8412"
+dependencies = [
+ "getrandom",
+ "libc",
+ "rand_chacha",
+ "rand_core",
+ "rand_hc",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "03a2a90da8c7523f554344f921aa97283eadf6ac484a6d2a7d0212fa7f8d6853"
+dependencies = [
+ "c2-chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "90bde5296fc891b0cef12a6d03ddccc162ce7b2aff54160af9338f8d40df6d19"
+dependencies = [
+ "getrandom",
+]
+
+[[package]]
+name = "rand_hc"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca3129af7b92a17112d59ad498c6f81eaf463253766b90396d39ea7a39d6613c"
+dependencies = [
+ "rand_core",
+]
+
+[[package]]
+name = "redox_syscall"
+version = "0.1.56"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2439c63f3f6139d1b57529d16bc3b8bb855230c8efcc5d3a896c8bea7c3b1e84"
+
 [[package]]
 name = "regex"
 version = "1.3.1"
@@ -238,6 +523,21 @@ version = "0.6.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "11a7e20d1cce64ef2fed88b66d347f88bd9babb82845b2b858f3edbf59a4f716"
 
+[[package]]
+name = "remove_dir_all"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4a83fa3702a688b9359eccba92d153ac33fd2e8462f9e0e3fdf155239ea7792e"
+dependencies = [
+ "winapi",
+]
+
+[[package]]
+name = "rustc-demangle"
+version = "0.1.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4c691c0e608126e00913e33f0ccf3727d5fc84573623b8d65b2df340b5201783"
+
 [[package]]
 name = "ryu"
 version = "1.0.2"
@@ -259,9 +559,9 @@ version = "1.0.104"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "128f9e303a5a29922045a830221b8f78ec74a5f544944f3d5984f8ec3895ef64"
 dependencies = [
- "proc-macro2",
- "quote",
- "syn",
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
 ]
 
 [[package]]
@@ -281,15 +581,52 @@ version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6e63cff320ae2c57904679ba7cb63280a3dc4613885beafb148ee7bf9aa9042d"
 
+[[package]]
+name = "syn"
+version = "0.15.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9ca4b3b69a77cbe1ffc9e198781b7acb0c7365a883670e8f1c1bc66fba79a5c5"
+dependencies = [
+ "proc-macro2 0.4.30",
+ "quote 0.6.13",
+ "unicode-xid 0.1.0",
+]
+
 [[package]]
 name = "syn"
 version = "1.0.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dff0acdb207ae2fe6d5976617f887eb1e35a2ba52c13c7234c790960cdad9238"
 dependencies = [
- "proc-macro2",
- "quote",
- "unicode-xid",
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "unicode-xid 0.2.0",
+]
+
+[[package]]
+name = "synstructure"
+version = "0.12.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "67656ea1dc1b41b1451851562ea232ec2e5a80242139f7e679ceccfb5d61f545"
+dependencies = [
+ "proc-macro2 1.0.6",
+ "quote 1.0.2",
+ "syn 1.0.11",
+ "unicode-xid 0.2.0",
+]
+
+[[package]]
+name = "tempfile"
+version = "3.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a6e24d9338a0a5be79593e2fa15a648add6138caa803e2d5bc782c371732ca9"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "rand",
+ "redox_syscall",
+ "remove_dir_all",
+ "winapi",
 ]
 
 [[package]]
@@ -301,6 +638,18 @@ dependencies = [
  "lazy_static",
 ]
 
+[[package]]
+name = "unicode-segmentation"
+version = "1.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e83e153d1053cbb5a118eeff7fd5be06ed99153f00dbcd8ae310c5fb2b22edc0"
+
+[[package]]
+name = "unicode-xid"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fc72304796d0818e357ead4e000d19c9c174ab23dc11093ac919054d20a6a7fc"
+
 [[package]]
 name = "unicode-xid"
 version = "0.2.0"
@@ -318,3 +667,41 @@ name = "version_check"
 version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "078775d0255232fb988e6fccf26ddc9d1ac274299aaedcedce21c6f72cc533ce"
+
+[[package]]
+name = "wasi"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b89c3ce4ce14bdc6fb6beaf9ec7928ca331de5df7e5ea278375642a2f478570d"
+
+[[package]]
+name = "which"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b57acb10231b9493c8472b20cb57317d0679a49e0bdbee44b3b803a6473af164"
+dependencies = [
+ "failure",
+ "libc",
+]
+
+[[package]]
+name = "winapi"
+version = "0.3.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8093091eeb260906a183e6ae1abdba2ef5ef2257a21801128899c3fc699229c6"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
diff --git a/rs/ankirs/Cargo.toml b/rs/ankirs/Cargo.toml
index 1981374cc..a9c34c962 100644
--- a/rs/ankirs/Cargo.toml
+++ b/rs/ankirs/Cargo.toml
@@ -3,3 +3,11 @@ name = "ankirs"
 version = "0.1.0"
 edition = "2018"
 authors = ["Ankitects Pty Ltd and contributors"]
+
+[dependencies]
+failure = "0.1.6"
+prost = "0.5.0"
+bytes = "0.4"
+
+[build-dependencies]
+prost-build = "0.5.0"
diff --git a/rs/ankirs/build.rs b/rs/ankirs/build.rs
new file mode 100644
index 000000000..c72a77327
--- /dev/null
+++ b/rs/ankirs/build.rs
@@ -0,0 +1,7 @@
+use prost_build;
+
+fn main() {
+    // avoid default OUT_DIR for now, for code completion
+    std::env::set_var("OUT_DIR", "src");
+    prost_build::compile_protos(&["../../proto/bridge.proto"], &["../../proto/"]).unwrap();
+}
diff --git a/rs/ankirs/src/bridge.rs b/rs/ankirs/src/bridge.rs
new file mode 100644
index 000000000..df5a8c5a3
--- /dev/null
+++ b/rs/ankirs/src/bridge.rs
@@ -0,0 +1,84 @@
+use crate::err::{AnkiError, Result};
+use crate::proto as pt;
+use crate::proto::bridge_input::Value;
+use prost::Message;
+
+pub struct Bridge {}
+
+impl Default for Bridge {
+    fn default() -> Self {
+        Bridge {}
+    }
+}
+
+/// Convert an Anki error to a protobuf error.
+impl std::convert::From<AnkiError> for pt::BridgeError {
+    fn from(err: AnkiError) -> Self {
+        use pt::bridge_error::Value as V;
+        let value = match err {
+            AnkiError::InvalidInput { info } => V::InvalidInput(pt::InvalidInputError { info }),
+        };
+
+        pt::BridgeError { value: Some(value) }
+    }
+}
+
+// Convert an Anki error to a protobuf output.
+impl std::convert::From<AnkiError> for pt::bridge_output::Value {
+    fn from(err: AnkiError) -> Self {
+        pt::bridge_output::Value::Error(err.into())
+    }
+}
+
+impl Bridge {
+    pub fn new() -> Bridge {
+        Bridge::default()
+    }
+
+    /// Decode a request, process it, and return the encoded result.
+    pub fn run_command_bytes(&mut self, req: &[u8]) -> Vec<u8> {
+        let mut buf = vec![];
+
+        let req = match pt::BridgeInput::decode(req) {
+            Ok(req) => req,
+            Err(_e) => {
+                // unable to decode
+                let err = AnkiError::invalid_input("couldn't decode bridge request");
+                let output = pt::BridgeOutput {
+                    value: Some(err.into()),
+                };
+                output.encode(&mut buf).expect("encode failed");
+                return buf;
+            }
+        };
+
+        let resp = self.run_command(req);
+        resp.encode(&mut buf).expect("encode failed");
+        buf
+    }
+
+    fn run_command(&self, input: pt::BridgeInput) -> pt::BridgeOutput {
+        let oval = if let Some(ival) = input.value {
+            match self.run_command_inner(ival) {
+                Ok(output) => output,
+                Err(err) => err.into(),
+            }
+        } else {
+            AnkiError::invalid_input("unrecognized bridge input value").into()
+        };
+
+        pt::BridgeOutput { value: Some(oval) }
+    }
+
+    fn run_command_inner(&self, ival: pt::bridge_input::Value) -> Result<pt::bridge_output::Value> {
+        use pt::bridge_output::Value as OValue;
+        Ok(match ival {
+            Value::PlusOne(input) => OValue::PlusOne(self.plus_one(input)?),
+        })
+    }
+
+    fn plus_one(&self, input: pt::PlusOneIn) -> Result<pt::PlusOneOut> {
+        let num = input.num + 1;
+        Ok(pt::PlusOneOut { num })
+    }
+}
diff --git a/rs/ankirs/src/err.rs b/rs/ankirs/src/err.rs
new file mode 100644
index 000000000..48b16d39e
--- /dev/null
+++ b/rs/ankirs/src/err.rs
@@ -0,0 +1,16 @@
+pub use failure::{Error, Fail};
+
+pub type Result<T> = std::result::Result<T, AnkiError>;
+
+#[derive(Debug, Fail)]
+pub enum AnkiError {
+    #[fail(display = "invalid input: {}", info)]
+    InvalidInput { info: String },
+}
+
+// error helpers
+impl AnkiError {
+    pub(crate) fn invalid_input<S: Into<String>>(s: S) -> AnkiError {
+        AnkiError::InvalidInput { info: s.into() }
+    }
+}
diff --git a/rs/ankirs/src/lib.rs b/rs/ankirs/src/lib.rs
index 8b1378917..eb1b6bf97 100644
--- a/rs/ankirs/src/lib.rs
+++ b/rs/ankirs/src/lib.rs
@@ -1 +1,4 @@
+mod proto;
 
+pub mod bridge;
+pub mod err;
diff --git a/rs/pybridge/Cargo.toml b/rs/pybridge/Cargo.toml
index 0af13556b..6b87a5c18 100644
--- a/rs/pybridge/Cargo.toml
+++ b/rs/pybridge/Cargo.toml
@@ -4,6 +4,9 @@ version = "0.1.0"
 edition = "2018"
 authors = ["Ankitects Pty Ltd and contributors"]
 
+[dependencies]
+ankirs = { path = "../ankirs" }
+
 [dependencies.pyo3]
 version = "0.8.0"
 features = ["extension-module"]
diff --git a/rs/pybridge/src/lib.rs b/rs/pybridge/src/lib.rs
index c56231b73..f48351bd0 100644
--- a/rs/pybridge/src/lib.rs
+++ b/rs/pybridge/src/lib.rs
@@ -1,19 +1,27 @@
-use pyo3::exceptions;
+use ankirs::bridge::Bridge as RustBridge;
 use pyo3::prelude::*;
+use pyo3::types::PyBytes;
 
 #[pyclass]
-struct Bridge {}
+struct Bridge {
+    bridge: RustBridge,
+}
 
 #[pymethods]
 impl Bridge {
     #[new]
     fn init(obj: &PyRawObject) {
-        obj.init({ Bridge {} });
+        obj.init({
+            Bridge {
+                bridge: Default::default(),
+            }
+        });
     }
 
-    fn cmd(&mut self, _request: String) -> PyResult<String> {
-        Ok("test".to_string())
-            .map_err(|e: std::io::Error| exceptions::Exception::py_err(format!("{:?}", e)))
+    fn command(&mut self, py: Python, input: &PyBytes) -> PyResult<PyObject> {
+        let out_bytes = self.bridge.run_command_bytes(input.as_bytes());
+        let out_obj = PyBytes::new(py, &out_bytes);
+        Ok(out_obj.into())
     }
 }
 
diff --git a/rs/rustfmt.toml b/rs/rustfmt.toml
new file mode 100644
index 000000000..c9dc0fc83
--- /dev/null
+++ b/rs/rustfmt.toml
@@ -0,0 +1 @@
+ignore = ["proto.rs"]