diff --git a/tools/go/BUILD b/tools/go/BUILD
index ec8aa26..1895ffe 100644
--- a/tools/go/BUILD
+++ b/tools/go/BUILD
@@ -1,5 +1,36 @@
-# This file exists to create a NOOP toolchain for Go on platforms that don't
-# support Go. We can probably get rid of this once
+py_library(
+    name = "mirror_lib",
+    srcs = [
+        "mirror_lib.py",
+    ],
+)
+
+py_binary(
+    name = "tweak_gazelle_go_deps",
+    srcs = [
+        "tweak_gazelle_go_deps.py",
+    ],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":mirror_lib",
+    ],
+)
+
+py_binary(
+    name = "mirror_go_repos",
+    srcs = [
+        "mirror_go_repos.py",
+    ],
+    data = [
+        "@go_sdk//:bin/go",
+    ],
+    deps = [
+        ":mirror_lib",
+    ],
+)
+
+# The remainder of this file exists to create a NOOP toolchain for Go on
+# platforms that don't support Go. We can probably get rid of this once
 # https://github.com/bazelbuild/bazel/issues/12897 is fixed.
 #
 # For platforms that do support Go, we use go_register_toolchain() in
diff --git a/tools/go/go_mirrors.bzl b/tools/go/go_mirrors.bzl
new file mode 100644
index 0000000..bee4c5b
--- /dev/null
+++ b/tools/go/go_mirrors.bzl
@@ -0,0 +1,318 @@
+# This file is auto-generated. Do not edit.
+GO_MIRROR_INFO = {
+  "co_honnef_go_tools": {
+    "filename": "co_honnef_go_tools__v0.0.0-20190523083050-ea95bdfd59fc.zip",
+    "importpath": "honnef.co/go/tools",
+    "sha256": "eeaa82700e96ac5e803d7a9c32363332504beff8fbb1202492b4d43d5a5e7360",
+    "strip_prefix": "honnef.co/go/tools@v0.0.0-20190523083050-ea95bdfd59fc",
+    "version": "v0.0.0-20190523083050-ea95bdfd59fc"
+  },
+  "com_github_antihax_optional": {
+    "filename": "com_github_antihax_optional__v1.0.0.zip",
+    "importpath": "github.com/antihax/optional",
+    "sha256": "15ab4d41bdbb72ee0ac63db616cdefc7671c79e13d0f73b58355a6a88219c97f",
+    "strip_prefix": "github.com/antihax/optional@v1.0.0",
+    "version": "v1.0.0"
+  },
+  "com_github_buildkite_go_buildkite": {
+    "filename": "com_github_buildkite_go_buildkite__v2.2.0+incompatible.zip",
+    "importpath": "github.com/buildkite/go-buildkite",
+    "sha256": "1871115c8c6db004e4b6e57cee927043bfc9ea0c56e7b8f8336021bd8bf588c4",
+    "strip_prefix": "github.com/buildkite/go-buildkite@v2.2.0+incompatible",
+    "version": "v2.2.0+incompatible"
+  },
+  "com_github_burntsushi_toml": {
+    "filename": "com_github_burntsushi_toml__v0.3.1.zip",
+    "importpath": "github.com/BurntSushi/toml",
+    "sha256": "815c6e594745f2d8842ff9a4b0569c6695e6cdfd5e07e5b3d98d06b72ca41e3c",
+    "strip_prefix": "github.com/BurntSushi/toml@v0.3.1",
+    "version": "v0.3.1"
+  },
+  "com_github_cenkalti_backoff": {
+    "filename": "com_github_cenkalti_backoff__v2.2.1+incompatible.zip",
+    "importpath": "github.com/cenkalti/backoff",
+    "sha256": "f8196815a1b4d25e5b8158029d5264801fc8aa5ff128ccf30752fd169693d43b",
+    "strip_prefix": "github.com/cenkalti/backoff@v2.2.1+incompatible",
+    "version": "v2.2.1+incompatible"
+  },
+  "com_github_census_instrumentation_opencensus_proto": {
+    "filename": "com_github_census_instrumentation_opencensus_proto__v0.2.1.zip",
+    "importpath": "github.com/census-instrumentation/opencensus-proto",
+    "sha256": "b3c09f3e635d47b4138695a547d1f2c7138f382cbe5a8b5865b66a8e08233461",
+    "strip_prefix": "github.com/census-instrumentation/opencensus-proto@v0.2.1",
+    "version": "v0.2.1"
+  },
+  "com_github_cespare_xxhash_v2": {
+    "filename": "com_github_cespare_xxhash_v2__v2.1.1.zip",
+    "importpath": "github.com/cespare/xxhash/v2",
+    "sha256": "5baa031c72e73e42617f0fd74e7d813344850bd6a6073381b6a4160a5e9cb59e",
+    "strip_prefix": "github.com/cespare/xxhash/v2@v2.1.1",
+    "version": "v2.1.1"
+  },
+  "com_github_client9_misspell": {
+    "filename": "com_github_client9_misspell__v0.3.4.zip",
+    "importpath": "github.com/client9/misspell",
+    "sha256": "a3af206372e131dd10a68ac470c66a1b18eaf51c6afacb55b2e2a06e39b90728",
+    "strip_prefix": "github.com/client9/misspell@v0.3.4",
+    "version": "v0.3.4"
+  },
+  "com_github_cncf_udpa_go": {
+    "filename": "com_github_cncf_udpa_go__v0.0.0-20210930031921-04548b0d99d4.zip",
+    "importpath": "github.com/cncf/udpa/go",
+    "sha256": "a449fa94e58117a79c17577e39f72f695c4876f74cbd9142d512278192ca90aa",
+    "strip_prefix": "github.com/cncf/udpa/go@v0.0.0-20210930031921-04548b0d99d4",
+    "version": "v0.0.0-20210930031921-04548b0d99d4"
+  },
+  "com_github_cncf_xds_go": {
+    "filename": "com_github_cncf_xds_go__v0.0.0-20211011173535-cb28da3451f1.zip",
+    "importpath": "github.com/cncf/xds/go",
+    "sha256": "eb86281e1e9cf6f83d25edbec0e3fd690570efa3414866d14c6a32b44931375d",
+    "strip_prefix": "github.com/cncf/xds/go@v0.0.0-20211011173535-cb28da3451f1",
+    "version": "v0.0.0-20211011173535-cb28da3451f1"
+  },
+  "com_github_davecgh_go_spew": {
+    "filename": "com_github_davecgh_go_spew__v1.1.0.zip",
+    "importpath": "github.com/davecgh/go-spew",
+    "sha256": "0b5a691aeb8b6af31bd2bb640973ea7e8bf1ed9bc5889da220bf44dc06d9692c",
+    "strip_prefix": "github.com/davecgh/go-spew@v1.1.0",
+    "version": "v1.1.0"
+  },
+  "com_github_envoyproxy_go_control_plane": {
+    "filename": "com_github_envoyproxy_go_control_plane__v0.9.10-0.20210907150352-cf90f659a021.zip",
+    "importpath": "github.com/envoyproxy/go-control-plane",
+    "sha256": "41dc70a8e658cb8945fa0de289d25dd7a608e99929bae144776781401dec507a",
+    "strip_prefix": "github.com/envoyproxy/go-control-plane@v0.9.10-0.20210907150352-cf90f659a021",
+    "version": "v0.9.10-0.20210907150352-cf90f659a021"
+  },
+  "com_github_envoyproxy_protoc_gen_validate": {
+    "filename": "com_github_envoyproxy_protoc_gen_validate__v0.1.0.zip",
+    "importpath": "github.com/envoyproxy/protoc-gen-validate",
+    "sha256": "ec5261f3bbc426d71e2be4c76063ba12460c5d27845d630763e9e911ec4768af",
+    "strip_prefix": "github.com/envoyproxy/protoc-gen-validate@v0.1.0",
+    "version": "v0.1.0"
+  },
+  "com_github_ghodss_yaml": {
+    "filename": "com_github_ghodss_yaml__v1.0.0.zip",
+    "importpath": "github.com/ghodss/yaml",
+    "sha256": "c3f295d23c02c0b35e4d3b29053586e737cf9642df9615da99c0bda9bbacc624",
+    "strip_prefix": "github.com/ghodss/yaml@v1.0.0",
+    "version": "v1.0.0"
+  },
+  "com_github_golang_glog": {
+    "filename": "com_github_golang_glog__v0.0.0-20160126235308-23def4e6c14b.zip",
+    "importpath": "github.com/golang/glog",
+    "sha256": "36b3c522c8102dfe74ca96e474c4c361750bf2bb85bc3cefe4f074c07d6825a9",
+    "strip_prefix": "github.com/golang/glog@v0.0.0-20160126235308-23def4e6c14b",
+    "version": "v0.0.0-20160126235308-23def4e6c14b"
+  },
+  "com_github_golang_mock": {
+    "filename": "com_github_golang_mock__v1.1.1.zip",
+    "importpath": "github.com/golang/mock",
+    "sha256": "636fd21575ebdfbebd53045802a40c780fdab33c6130cea9279346898286f1ca",
+    "strip_prefix": "github.com/golang/mock@v1.1.1",
+    "version": "v1.1.1"
+  },
+  "com_github_golang_protobuf": {
+    "filename": "com_github_golang_protobuf__v1.5.2.zip",
+    "importpath": "github.com/golang/protobuf",
+    "sha256": "5d1c817bebc1202ab3b42a418e584e0008e8027baf212ce69c2ae3e9e7b8c64b",
+    "strip_prefix": "github.com/golang/protobuf@v1.5.2",
+    "version": "v1.5.2"
+  },
+  "com_github_google_go_cmp": {
+    "filename": "com_github_google_go_cmp__v0.5.5.zip",
+    "importpath": "github.com/google/go-cmp",
+    "sha256": "0ee90a7194c025d849699f897d97641b8676ceca9215c96e00eaf1f0e6e953ad",
+    "strip_prefix": "github.com/google/go-cmp@v0.5.5",
+    "version": "v0.5.5"
+  },
+  "com_github_google_go_querystring": {
+    "filename": "com_github_google_go_querystring__v1.1.0.zip",
+    "importpath": "github.com/google/go-querystring",
+    "sha256": "a6aafc01f5602e6177928751074e325792a654e1d92f0e238b8e8739656dd72b",
+    "strip_prefix": "github.com/google/go-querystring@v1.1.0",
+    "version": "v1.1.0"
+  },
+  "com_github_google_uuid": {
+    "filename": "com_github_google_uuid__v1.1.2.zip",
+    "importpath": "github.com/google/uuid",
+    "sha256": "5d52fee1f44cf85dbba03f1bd6098a15a131e32c0e45839b352d69aceb7babfc",
+    "strip_prefix": "github.com/google/uuid@v1.1.2",
+    "version": "v1.1.2"
+  },
+  "com_github_grpc_ecosystem_grpc_gateway": {
+    "filename": "com_github_grpc_ecosystem_grpc_gateway__v1.16.0.zip",
+    "importpath": "github.com/grpc-ecosystem/grpc-gateway",
+    "sha256": "377b03aef288b34ed894449d3ddba40d525dd7fb55de6e79045cdf499e7fe565",
+    "strip_prefix": "github.com/grpc-ecosystem/grpc-gateway@v1.16.0",
+    "version": "v1.16.0"
+  },
+  "com_github_pmezard_go_difflib": {
+    "filename": "com_github_pmezard_go_difflib__v1.0.0.zip",
+    "importpath": "github.com/pmezard/go-difflib",
+    "sha256": "de04cecc1a4b8d53e4357051026794bcbc54f2e6a260cfac508ce69d5d6457a0",
+    "strip_prefix": "github.com/pmezard/go-difflib@v1.0.0",
+    "version": "v1.0.0"
+  },
+  "com_github_prometheus_client_model": {
+    "filename": "com_github_prometheus_client_model__v0.0.0-20190812154241-14fe0d1b01d4.zip",
+    "importpath": "github.com/prometheus/client_model",
+    "sha256": "5d4719be47f4f69ab5bf36a04c75eb078a0f69b43a335f400c2d688ac9e61795",
+    "strip_prefix": "github.com/prometheus/client_model@v0.0.0-20190812154241-14fe0d1b01d4",
+    "version": "v0.0.0-20190812154241-14fe0d1b01d4"
+  },
+  "com_github_rogpeppe_fastuuid": {
+    "filename": "com_github_rogpeppe_fastuuid__v1.2.0.zip",
+    "importpath": "github.com/rogpeppe/fastuuid",
+    "sha256": "f9b8293f5e20270e26fb4214ca7afec864de92c73d03ff62b5ee29d1db4e72a1",
+    "strip_prefix": "github.com/rogpeppe/fastuuid@v1.2.0",
+    "version": "v1.2.0"
+  },
+  "com_github_stretchr_objx": {
+    "filename": "com_github_stretchr_objx__v0.1.0.zip",
+    "importpath": "github.com/stretchr/objx",
+    "sha256": "1fa10dab404ed7fc8ed2a033f8784187d5df3513ced3841ce39e46d37850eb1d",
+    "strip_prefix": "github.com/stretchr/objx@v0.1.0",
+    "version": "v0.1.0"
+  },
+  "com_github_stretchr_testify": {
+    "filename": "com_github_stretchr_testify__v1.7.0.zip",
+    "importpath": "github.com/stretchr/testify",
+    "sha256": "5a46ccebeff510df3e2f6d3842ee79d3f68d0e7b1554cd6ee93390d68b6c6b34",
+    "strip_prefix": "github.com/stretchr/testify@v1.7.0",
+    "version": "v1.7.0"
+  },
+  "com_google_cloud_go": {
+    "filename": "com_google_cloud_go__v0.34.0.zip",
+    "importpath": "cloud.google.com/go",
+    "sha256": "27c1190dcd33c594838487544d8c3d17df4f7916fb542f5c2c9ca729ef1d9fe6",
+    "strip_prefix": "cloud.google.com/go@v0.34.0",
+    "version": "v0.34.0"
+  },
+  "in_gopkg_check_v1": {
+    "filename": "in_gopkg_check_v1__v0.0.0-20161208181325-20d25e280405.zip",
+    "importpath": "gopkg.in/check.v1",
+    "sha256": "4e1817f964ca34e545b81afda0325a5e89cf58de2e413d8207c0afddd0fdc15c",
+    "strip_prefix": "gopkg.in/check.v1@v0.0.0-20161208181325-20d25e280405",
+    "version": "v0.0.0-20161208181325-20d25e280405"
+  },
+  "in_gopkg_yaml_v2": {
+    "filename": "in_gopkg_yaml_v2__v2.2.3.zip",
+    "importpath": "gopkg.in/yaml.v2",
+    "sha256": "213403de27ae981b118ba199a3a1ddc64a82d0c9cf7534b762dc9ee5d79c5316",
+    "strip_prefix": "gopkg.in/yaml.v2@v2.2.3",
+    "version": "v2.2.3"
+  },
+  "in_gopkg_yaml_v3": {
+    "filename": "in_gopkg_yaml_v3__v3.0.0-20200313102051-9f266ea9e77c.zip",
+    "importpath": "gopkg.in/yaml.v3",
+    "sha256": "acf19ccb4fca983b234a39ef032faf9ab70e759680673bb3dff077e77fee20fe",
+    "strip_prefix": "gopkg.in/yaml.v3@v3.0.0-20200313102051-9f266ea9e77c",
+    "version": "v3.0.0-20200313102051-9f266ea9e77c"
+  },
+  "io_opentelemetry_go_proto_otlp": {
+    "filename": "io_opentelemetry_go_proto_otlp__v0.7.0.zip",
+    "importpath": "go.opentelemetry.io/proto/otlp",
+    "sha256": "a7db0590bc4c5f0b9b99cc958decf644f1e5cc11e0b995dc20b3583a2215259b",
+    "strip_prefix": "go.opentelemetry.io/proto/otlp@v0.7.0",
+    "version": "v0.7.0"
+  },
+  "org_golang_google_appengine": {
+    "filename": "org_golang_google_appengine__v1.4.0.zip",
+    "importpath": "google.golang.org/appengine",
+    "sha256": "d4dba839844a92bd9355812a53f086ff3301aa8f59b29a3e2f799d27be8db71f",
+    "strip_prefix": "google.golang.org/appengine@v1.4.0",
+    "version": "v1.4.0"
+  },
+  "org_golang_google_genproto": {
+    "filename": "org_golang_google_genproto__v0.0.0-20200526211855-cb27e3aa2013.zip",
+    "importpath": "google.golang.org/genproto",
+    "sha256": "50336913c7325576ed9c3587fdcacd39094013af95c8c11736f335969136527d",
+    "strip_prefix": "google.golang.org/genproto@v0.0.0-20200526211855-cb27e3aa2013",
+    "version": "v0.0.0-20200526211855-cb27e3aa2013"
+  },
+  "org_golang_google_grpc": {
+    "filename": "org_golang_google_grpc__v1.43.0.zip",
+    "importpath": "google.golang.org/grpc",
+    "sha256": "19fa6e227e62e3ae9791ab81b8a784e93cc68860b7fe0e85dd8d3cfbc1b24398",
+    "strip_prefix": "google.golang.org/grpc@v1.43.0",
+    "version": "v1.43.0"
+  },
+  "org_golang_google_protobuf": {
+    "filename": "org_golang_google_protobuf__v1.26.0.zip",
+    "importpath": "google.golang.org/protobuf",
+    "sha256": "d7bc5de329bd4e803f7a2acfcbe8f2eba4ef1579485056ef569a4b245bee1208",
+    "strip_prefix": "google.golang.org/protobuf@v1.26.0",
+    "version": "v1.26.0"
+  },
+  "org_golang_x_crypto": {
+    "filename": "org_golang_x_crypto__v0.0.0-20200622213623-75b288015ac9.zip",
+    "importpath": "golang.org/x/crypto",
+    "sha256": "aeaac2684d693207a90f491b0303e881e58c014e96d27b0ebb7fe6937dfc1e76",
+    "strip_prefix": "golang.org/x/crypto@v0.0.0-20200622213623-75b288015ac9",
+    "version": "v0.0.0-20200622213623-75b288015ac9"
+  },
+  "org_golang_x_exp": {
+    "filename": "org_golang_x_exp__v0.0.0-20190121172915-509febef88a4.zip",
+    "importpath": "golang.org/x/exp",
+    "sha256": "c3a7dcc2e8117e749c6badc91d492de3ee2f5b440b30481a0a75f9d63db6fe0b",
+    "strip_prefix": "golang.org/x/exp@v0.0.0-20190121172915-509febef88a4",
+    "version": "v0.0.0-20190121172915-509febef88a4"
+  },
+  "org_golang_x_lint": {
+    "filename": "org_golang_x_lint__v0.0.0-20190313153728-d0100b6bd8b3.zip",
+    "importpath": "golang.org/x/lint",
+    "sha256": "5c7bb9792bdc4ec4cf1af525cf9998f8a958daf6495852c9a7dbb71738f2f10a",
+    "strip_prefix": "golang.org/x/lint@v0.0.0-20190313153728-d0100b6bd8b3",
+    "version": "v0.0.0-20190313153728-d0100b6bd8b3"
+  },
+  "org_golang_x_net": {
+    "filename": "org_golang_x_net__v0.0.0-20200822124328-c89045814202.zip",
+    "importpath": "golang.org/x/net",
+    "sha256": "22ea306ad6c9100c636c165dc05a64265d0f985452a9f1edf32b561b620ae762",
+    "strip_prefix": "golang.org/x/net@v0.0.0-20200822124328-c89045814202",
+    "version": "v0.0.0-20200822124328-c89045814202"
+  },
+  "org_golang_x_oauth2": {
+    "filename": "org_golang_x_oauth2__v0.0.0-20200107190931-bf48bf16ab8d.zip",
+    "importpath": "golang.org/x/oauth2",
+    "sha256": "661e4c30b15e488b434b19085567e581eb7bde892f04a0a3ab7ef94c0028f133",
+    "strip_prefix": "golang.org/x/oauth2@v0.0.0-20200107190931-bf48bf16ab8d",
+    "version": "v0.0.0-20200107190931-bf48bf16ab8d"
+  },
+  "org_golang_x_sync": {
+    "filename": "org_golang_x_sync__v0.0.0-20190423024810-112230192c58.zip",
+    "importpath": "golang.org/x/sync",
+    "sha256": "dc105c2b4d6c7ab48e54946ce2f624e8d1f5d47270eff1e88fed06cc65f91fb4",
+    "strip_prefix": "golang.org/x/sync@v0.0.0-20190423024810-112230192c58",
+    "version": "v0.0.0-20190423024810-112230192c58"
+  },
+  "org_golang_x_sys": {
+    "filename": "org_golang_x_sys__v0.0.0-20200323222414-85ca7c5b95cd.zip",
+    "importpath": "golang.org/x/sys",
+    "sha256": "d00ccd67cf0f2dd8622ed2721b8824fcbaf4f5730f47387fd5e39adbd5f6972e",
+    "strip_prefix": "golang.org/x/sys@v0.0.0-20200323222414-85ca7c5b95cd",
+    "version": "v0.0.0-20200323222414-85ca7c5b95cd"
+  },
+  "org_golang_x_text": {
+    "filename": "org_golang_x_text__v0.3.0.zip",
+    "importpath": "golang.org/x/text",
+    "sha256": "ea3068395503d3c7ef8ce16a286f75c8c93882c25a66c2aa6c8e2ad4da7a9ae0",
+    "strip_prefix": "golang.org/x/text@v0.3.0",
+    "version": "v0.3.0"
+  },
+  "org_golang_x_tools": {
+    "filename": "org_golang_x_tools__v0.0.0-20190524140312-2c0ae7006135.zip",
+    "importpath": "golang.org/x/tools",
+    "sha256": "86687e8cd5adccf8809ba031e59146d0c89047b6267aacc785ffc20b0ce6b735",
+    "strip_prefix": "golang.org/x/tools@v0.0.0-20190524140312-2c0ae7006135",
+    "version": "v0.0.0-20190524140312-2c0ae7006135"
+  },
+  "org_golang_x_xerrors": {
+    "filename": "org_golang_x_xerrors__v0.0.0-20200804184101-5ec99f83aff1.zip",
+    "importpath": "golang.org/x/xerrors",
+    "sha256": "380aaa3368ae165628bb487cf4e695a55c1420072b8b7a6f59c122f6a23bb255",
+    "strip_prefix": "golang.org/x/xerrors@v0.0.0-20200804184101-5ec99f83aff1",
+    "version": "v0.0.0-20200804184101-5ec99f83aff1"
+  }
+}
diff --git a/tools/go/mirror_go_repos.py b/tools/go/mirror_go_repos.py
new file mode 100644
index 0000000..dc160fa
--- /dev/null
+++ b/tools/go/mirror_go_repos.py
@@ -0,0 +1,144 @@
+"""This script mirrors the dependencies from go_deps.bzl as Build-Dependencies.
+
+We use "go mod download" to manually download each Go dependency. We then tar
+up all the dependencies and copy them to the Build-Dependencies server for
+hosting.
+"""
+
+import argparse
+import hashlib
+import json
+import os
+from pathlib import Path
+import subprocess
+import sys
+import tarfile
+from typing import List, Dict
+import urllib.request
+
+import tools.go.mirror_lib
+
+GO_DEPS_WWWW_DIR = "/var/www/html/files/frc971/Build-Dependencies/go_deps"
+
+def compute_sha256(filepath: str) -> str:
+    """Computes the SHA256 of a file at the specified location."""
+    with open(filepath, "rb") as file:
+        contents = file.read()
+    return hashlib.sha256(contents).hexdigest()
+
+def get_existing_mirrored_repos(ssh_host: str) -> Dict[str, str]:
+    """Gathers information about the libraries that are currently mirrored."""
+    run_result = subprocess.run(["ssh", ssh_host, f"bash -c 'sha256sum {GO_DEPS_WWWW_DIR}/*'"], check=True, stdout=subprocess.PIPE)
+
+    existing_mirrored_repos = {}
+    for line in run_result.stdout.decode("utf-8").splitlines():
+        sha256, fullpath = line.split()
+        existing_mirrored_repos[Path(fullpath).name] = sha256
+
+    return existing_mirrored_repos
+
+def download_repos(
+        repos: Dict[str, str],
+        existing_mirrored_repos: Dict[str, str],
+        tar: tarfile.TarFile) -> Dict[str, str]:
+    """Downloads the not-yet-mirrored repos into a tarball."""
+    cached_info = {}
+
+    for repo in repos:
+        print(f"Downloading file for {repo['name']}")
+        importpath = repo["importpath"]
+        version = repo["version"]
+        module = f"{importpath}@{version}"
+
+        download_result = subprocess.run(
+            ["external/go_sdk/bin/go", "mod", "download", "-json", module],
+            check=True, stdout=subprocess.PIPE)
+        if download_result.returncode != 0:
+            print("Failed to download file.")
+            return 1
+
+        module_info = json.loads(download_result.stdout.decode("utf-8"))
+
+        name = repo["name"]
+        zip_path = Path(module_info["Zip"])
+        mirrored_name = f"{name}__{zip_path.name}"
+        if mirrored_name not in existing_mirrored_repos:
+            # We only add the Go library to the tarball if it's not already
+            # mirrored. We don't want to overwrite files.
+            tar.add(zip_path, arcname=mirrored_name)
+            sha256 = compute_sha256(zip_path)
+        else:
+            # Use the already-computed checksum for consistency.
+            sha256 = existing_mirrored_repos[mirrored_name]
+
+        cached_info[name] = {
+            "strip_prefix": module,
+            "filename": mirrored_name,
+            "sha256": sha256,
+            "version": version,
+            "importpath": importpath,
+        }
+
+    return cached_info
+
+def copy_to_host_and_unpack(filename: str, ssh_host: str) -> None:
+    subprocess.run(["scp", filename, f"{ssh_host}:"], check=True)
+
+    # Be careful not to use single quotes in these commands to avoid breaking
+    # the subprocess.run() invocation below.
+    command = " && ".join([
+        f"tar -C {GO_DEPS_WWWW_DIR} --no-same-owner -xvaf {filename}",
+        # Change the permissions so other users can read them (and checksum
+        # them).
+        f"find {GO_DEPS_WWWW_DIR}/ -type f -exec chmod 644 {{}} +",
+    ])
+
+    print("You might be asked for your sudo password shortly.")
+    subprocess.run(["ssh", "-t", ssh_host, f"sudo -u www-data bash -c '{command}'"], check=True)
+
+def main(argv):
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "--ssh_host",
+        type=str,
+        help=("The SSH host to copy the downloaded Go repositories to. This "
+              "should be software.971spartans.net where all the "
+              "Build-Dependencies files live. Only specify this if you have "
+              "access to the server."))
+    parser.add_argument("--go_deps_bzl", type=str, default="go_deps.bzl")
+    parser.add_argument("--go_mirrors_bzl", type=str, default="tools/go/go_mirrors.bzl")
+    args = parser.parse_args(argv[1:])
+
+    os.chdir(os.environ["BUILD_WORKSPACE_DIRECTORY"])
+
+    repos = tools.go.mirror_lib.parse_go_repositories(args.go_deps_bzl)
+
+    if args.ssh_host:
+        existing_mirrored_repos = get_existing_mirrored_repos(args.ssh_host)
+    else:
+        existing_mirrored_repos = {}
+
+    with tarfile.open("go_deps.tar", "w") as tar:
+        cached_info = download_repos(repos, existing_mirrored_repos, tar)
+        num_not_already_mirrored = len(tar.getnames())
+
+    print(f"Found {num_not_already_mirrored}/{len(cached_info)} libraries "
+          "that need to be mirrored.")
+
+    # Only mirror the deps if we've specified an SSH host and we actually have
+    # something to mirror.
+    if args.ssh_host and num_not_already_mirrored:
+        copy_to_host_and_unpack("go_deps.tar", args.ssh_host)
+    else:
+        print("Skipping mirroring because of lack of --ssh_host or there's "
+              "nothing to actually mirror.")
+
+    with open(args.go_mirrors_bzl, "w") as file:
+        file.write("# This file is auto-generated. Do not edit.\n")
+        file.write("GO_MIRROR_INFO = ")
+        json.dump(cached_info, file, indent=2, sort_keys=True)
+        file.write("\n")
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))
diff --git a/tools/go/mirror_lib.py b/tools/go/mirror_lib.py
new file mode 100644
index 0000000..faad896
--- /dev/null
+++ b/tools/go/mirror_lib.py
@@ -0,0 +1,41 @@
+"""Provides helper functions for mirroring Go repositories."""
+
+import unittest.mock
+from typing import List, Dict
+
+
+def read_file(filepath: str) -> str:
+    """Reads an entire file by returning its contents as a string."""
+    with open(filepath, "r") as file:
+        return file.read()
+
+def parse_go_repositories(filepath: str) -> List[Dict[str, str]]:
+    """Parses the top-level go_deps.bzl file.
+
+    This function can parse both the original version of the file generated by
+    gazelle as well as the tweaked version generated by
+    tweak_gazelle_go_deps.py. The two versions are identical other than what function they call.
+    """
+    global_functions = {
+        "load": unittest.mock.MagicMock(),
+        # The gazelle generated version uses go_repository().
+        "go_repository": unittest.mock.MagicMock(),
+        # The tweak_gazelle_go_deps.py generated version uses
+        # maybe_override_go_dep().
+        "maybe_override_go_dep": unittest.mock.MagicMock()
+    }
+    compiled_code = compile(read_file(filepath), filepath, "exec")
+    eval(compiled_code, global_functions)
+
+    # Extract the repositories defined in the go_dependencies() function from
+    # go_deps.bzl.
+    global_functions["go_dependencies"]()
+
+    repositories = []
+    for repo_kind in ("go_repository", "maybe_override_go_dep"):
+        for repo in global_functions[repo_kind].mock_calls:
+            _, _, kwargs = repo
+            repositories.append(kwargs)
+
+    return repositories
+
diff --git a/tools/go/mirrored_go_deps.bzl b/tools/go/mirrored_go_deps.bzl
new file mode 100644
index 0000000..d77ce5c
--- /dev/null
+++ b/tools/go/mirrored_go_deps.bzl
@@ -0,0 +1,47 @@
+load("//tools/go:go_mirrors.bzl", "GO_MIRROR_INFO")
+load("@bazel_gazelle//:deps.bzl", "go_repository")
+load("@ci_configure//:ci.bzl", "RUNNING_IN_CI")
+
+def maybe_override_go_dep(name, importpath, sum, version):
+    """This macro selects between our dependency mirrors and upstream sources.
+
+    We want to use the mirrored version whenever possible. In CI we are required
+    to use the mirrored version. For local development we only use the mirrored
+    version if it's available. Otherwise we download from the upstream sources.
+    """
+    if not RUNNING_IN_CI:
+        override_go_dep = not (name in GO_MIRROR_INFO and GO_MIRROR_INFO[name]["version"] == version)
+    else:
+        override_go_dep = False
+        if name not in GO_MIRROR_INFO or GO_MIRROR_INFO[name]["version"] != version:
+            fail(("The repo {} is not properly mirrored. " +
+                  "Please ask someone with mirroring access for help." +
+                  "They need to 'bazel run //tools/go:mirror_go_repos -- " +
+                  "--ssh_host <software.971spartans.net>'.").format(name))
+
+    # If we want to use the upstream version and we've already imported a
+    # mirrored version via mirrored_go_dependencies(), then we override it here
+    # by giving the upstream version the same name.
+    if override_go_dep:
+        go_repository(
+            name = name,
+            importpath = importpath,
+            sum = sum,
+            version = version,
+        )
+
+
+def mirrored_go_dependencies():
+    """Sets up the Go dependencies we've mirrored."""
+    for name in GO_MIRROR_INFO:
+        info = GO_MIRROR_INFO[name]
+        go_repository(
+            name = name,
+            strip_prefix = info["strip_prefix"],
+            type = "zip",
+            urls = [
+                "https://www.frc971.org/Build-Dependencies/go_deps/" + info["filename"],
+            ],
+            sha256 = info["sha256"],
+            importpath = info["importpath"],
+        )
diff --git a/tools/go/tweak_gazelle_go_deps.py b/tools/go/tweak_gazelle_go_deps.py
new file mode 100644
index 0000000..7189d43
--- /dev/null
+++ b/tools/go/tweak_gazelle_go_deps.py
@@ -0,0 +1,42 @@
+"""Tweaks the gazelle-generated go_deps.bzl to work with our mirrors.
+
+This script changes all invocations of go_repository() in go_deps.bzl to use
+maybe_override_go_dep(). That lets us more easily switch between upstream
+sources and our mirrored versions of the code.
+
+The motivation is to let folks use upstream sources during local development.
+For CI runs, however, we have to restrict ourselves to mirrored dependencies.
+"""
+
+import argparse
+import sys
+import textwrap
+
+import tools.go.mirror_lib
+
+def main(argv):
+    parser = argparse.ArgumentParser()
+    parser.add_argument("go_deps_bzl", type=str)
+    args = parser.parse_args(argv[1:])
+
+    repos = tools.go.mirror_lib.parse_go_repositories(args.go_deps_bzl)
+
+    with open(args.go_deps_bzl, "w") as file:
+        file.write(textwrap.dedent("""\
+            # This file is auto-generated. Do not edit.
+            load("//tools/go:mirrored_go_deps.bzl", "maybe_override_go_dep")
+
+            def go_dependencies():
+            """))
+        for repo in repos:
+            file.write(textwrap.indent(textwrap.dedent(f"""\
+                maybe_override_go_dep(
+                    name = "{repo['name']}",
+                    importpath = "{repo['importpath']}",
+                    sum = "{repo['sum']}",
+                    version = "{repo['version']}",
+                )
+                """), " " * 4))
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))