diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
index cd6af4f1ff63da40d06395d80e9a7970edad256f..357c314adb7a3dfb511ab87f4dfb19d7cb92996e 100644
--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -28,7 +28,7 @@ CI must pass on your changes for them to be merged.
 ### CI
 
 CI will ensure your code is formatted, lints and passes tests.
-It will collect coverage and report it to [codecov](https://codecov.io/gh/nhooyr/websocket)
+It will collect coverage and report it to [coveralls](https://coveralls.io/github/nhooyr/websocket)
 and also upload a html `coverage` artifact that you can download to browse coverage.
 
 You can run CI locally.
@@ -42,7 +42,4 @@ See [ci/image/Dockerfile](../ci/image/Dockerfile) for the installation of the CI
 
 For coverage details locally, see `ci/out/coverage.html` after running `make test`.
 
-You can also run tests normally with `go test`. `make test` just passes a default set of flags to
-`go test` to collect coverage and runs the WASM tests.
-
-Coverage percentage from codecov and the CI scripts will be different because they are calculated differently.
+You can run tests normally with `go test`. `make test` wraps around `go test` to collect coverage.
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 37282e1bf14f7be539c422b1029864f21a071219..d13e90285dfe5d40d639b2a1699ac5e3eced8c48 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -21,7 +21,7 @@ jobs:
       - uses: actions/checkout@v1
       - run: make test
         env:
-          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+          COVERALLS_TOKEN: ${{ secrets.COVERALLS_TOKEN }}
       - name: Upload coverage.html
         uses: actions/upload-artifact@master
         with:
diff --git a/Makefile b/Makefile
index ce92ab5ba82b546c53e7aa13d91296cd11d50bcc..62633e3938ef727f01e987a5979a9260b22cdccf 100644
--- a/Makefile
+++ b/Makefile
@@ -4,6 +4,10 @@ all: fmt lint test
 
 .PHONY: *
 
+.ONESHELL:
+SHELL = bash
+.SHELLFLAGS = -ceuo pipefail
+
 include ci/fmt.mk
 include ci/lint.mk
 include ci/test.mk
diff --git a/README.md b/README.md
index 9dd5d0a8a23e2b23fc6cc1b621f6dc46b88aaca0..4a425a1658711cfa4654477a7f43e4bab80df517 100644
--- a/README.md
+++ b/README.md
@@ -1,8 +1,8 @@
 # websocket
 
-[![GitHub release (latest SemVer)](https://img.shields.io/github/v/release/nhooyr/websocket?color=6b9ded&sort=semver)](https://github.com/nhooyr/websocket/releases)
+[![GitHub Release](https://img.shields.io/github/v/release/nhooyr/websocket?color=6b9ded&sort=semver)](https://github.com/nhooyr/websocket/releases)
 [![GoDoc](https://godoc.org/nhooyr.io/websocket?status.svg)](https://godoc.org/nhooyr.io/websocket)
-[![Codecov](https://img.shields.io/codecov/c/github/nhooyr/websocket.svg?color=65d6a4)](https://codecov.io/gh/nhooyr/websocket)
+[![Codecov](https://img.shields.io/coveralls/github/nhooyr/websocket?color=65d6a4)](https://coveralls.io/github/nhooyr/websocket)
 [![Actions Status](https://github.com/nhooyr/websocket/workflows/ci/badge.svg)](https://github.com/nhooyr/websocket/actions)
 
 websocket is a minimal and idiomatic WebSocket library for Go.
diff --git a/ci/.codecov.yml b/ci/.codecov.yml
deleted file mode 100644
index fa7c5f0aaf70065a23fc30c345a5c7c3ed814b80..0000000000000000000000000000000000000000
--- a/ci/.codecov.yml
+++ /dev/null
@@ -1,10 +0,0 @@
-comment: off
-coverage:
-  status:
-    # Prevent small changes in coverage from failing CI.
-    project:
-      default:
-        threshold: 15%
-    patch:
-      default:
-        threshold: 100%
diff --git a/ci/fmt.mk b/ci/fmt.mk
index 16a3b24e365e2175cf97ff66c5f2bd42c90928f0..8e61bc243c608d0eea502d90861c2650d9d34223 100644
--- a/ci/fmt.mk
+++ b/ci/fmt.mk
@@ -1,6 +1,12 @@
-fmt: modtidy gofmt goimports prettier shfmt
+fmt: modtidy gofmt goimports prettier
 ifdef CI
-	./ci/fmtcheck.sh
+	if [[ $$(git ls-files --other --modified --exclude-standard) != "" ]]; then
+	  echo "Files need generation or are formatted incorrectly:"
+	  git -c color.ui=always status | grep --color=no '\e\[31m'
+	  echo "Please run the following locally:"
+	  echo "  make fmt"
+	  exit 1
+	fi
 endif
 
 modtidy: gen
@@ -12,11 +18,8 @@ gofmt: gen
 goimports: gen
 	goimports -w "-local=$$(go list -m)" .
 
-prettier: gen
-	prettier --write --print-width=120 --no-semi --trailing-comma=all --loglevel=warn $$(git ls-files "*.yaml" "*.yml" "*.md" "*.ts")
-
-shfmt: gen
-	shfmt -i 2 -w -s -sr .
+prettier:
+	prettier --write --print-width=120 --no-semi --trailing-comma=all --loglevel=warn $$(git ls-files "*.yml" "*.md")
 
 gen:
 	go generate ./...
diff --git a/ci/fmtcheck.sh b/ci/fmtcheck.sh
deleted file mode 100755
index 6e452a382da25ffedb6dc012214d37baa8614371..0000000000000000000000000000000000000000
--- a/ci/fmtcheck.sh
+++ /dev/null
@@ -1,11 +0,0 @@
-#!/usr/bin/env bash
-
-set -euo pipefail
-
-if [[ $(git ls-files --other --modified --exclude-standard) != "" ]]; then
-  echo "Files need generation or are formatted incorrectly."
-  git status
-  echo "Please run the following locally:"
-  echo "  make fmt"
-  exit 1
-fi
diff --git a/ci/image/Dockerfile b/ci/image/Dockerfile
index 7fd5544a0018672a6394762a03f892bad64dd461..183c9e43f851ab72d7bd82eca1d2b29401645b6b 100644
--- a/ci/image/Dockerfile
+++ b/ci/image/Dockerfile
@@ -3,7 +3,6 @@ FROM golang:1
 RUN apt-get update
 RUN apt-get install -y chromium
 RUN apt-get install -y npm
-RUN apt-get install -y shellcheck
 
 ENV GOPATH=/root/gopath
 ENV PATH=$GOPATH/bin:$PATH
@@ -13,14 +12,13 @@ ENV CI=true
 ENV MAKEFLAGS="--jobs=8 --output-sync=target"
 
 COPY ./ci/image/gitignore /root/.config/git/ignore
-RUN git config --system color.ui always
 
 RUN npm install -g prettier
 RUN go get golang.org/x/tools/cmd/stringer
 RUN go get golang.org/x/tools/cmd/goimports
-RUN go get mvdan.cc/sh/cmd/shfmt
 RUN go get golang.org/x/lint/golint
 RUN go get github.com/agnivade/wasmbrowsertest
+RUN go get github.com/mattn/goveralls
 
 # Cache go modules and build cache.
 COPY . /tmp/websocket
diff --git a/ci/lint.mk b/ci/lint.mk
index f68add4176bb4ec5db3ff4174dd1c00bae44c83d..a656ea8db7374fd4d0b178abb71f8730ab9600a0 100644
--- a/ci/lint.mk
+++ b/ci/lint.mk
@@ -1,4 +1,4 @@
-lint: govet golint govet-wasm golint-wasm shellcheck
+lint: govet golint govet-wasm golint-wasm
 
 govet:
 	go vet ./...
@@ -11,6 +11,3 @@ golint:
 
 golint-wasm:
 	GOOS=js GOARCH=wasm golint -set_exit_status ./...
-
-shellcheck:
-	shellcheck -x $$(git ls-files "*.sh")
diff --git a/ci/test.mk b/ci/test.mk
index 8d46c94a61a0022078952928e76d2022a0094f4c..cebada778e4ac37cb5ad1aa0988da77af80abeb6 100644
--- a/ci/test.mk
+++ b/ci/test.mk
@@ -1,18 +1,17 @@
-test: gotest
-
-gotest: _gotest htmlcov
+test: gotest ci/out/coverage.html
 ifdef CI
-gotest: codecov
+test: coveralls
 endif
 
-htmlcov: _gotest
+ci/out/coverage.html: gotest
 	go tool cover -html=ci/out/coverage.prof -o=ci/out/coverage.html
 
-codecov: _gotest
-	curl -s https://codecov.io/bash | bash -s -- -Z -f ci/out/coverage.prof
+coveralls: gotest
+	echo "--- coveralls"
+	goveralls -coverprofile=ci/out/coverage.prof -service=github-actions
 
-_gotest:
-	go test -parallel=32 -coverprofile=ci/out/coverage.prof -coverpkg=./... $$TESTFLAGS ./...
+gotest:
+	go test -parallel=32 -covermode=count -coverprofile=ci/out/coverage.prof -coverpkg=./... $${TESTFLAGS-} ./...
 	sed -i '/_stringer\.go/d' ci/out/coverage.prof
 	sed -i '/wsecho\.go/d' ci/out/coverage.prof
 	sed -i '/assert\.go/d' ci/out/coverage.prof