diff --git a/.golangci.yml b/.golangci.yml
index 4460be7..c32e59b 100644
--- a/.golangci.yml
+++ b/.golangci.yml
@@ -39,12 +39,15 @@ linters:
     - gosimple
     - govet
     - ineffassign
+    # - mirror  # requires golangci-lint 1.53
     - misspell
     - staticcheck
     - structcheck
+    - thelper
     - typecheck
     - unparam
     - unused
+    - usestdlibvars
     - varcheck
 
 linters-settings:
diff --git a/main.go b/main.go
index f94ac0c..1cda1c1 100644
--- a/main.go
+++ b/main.go
@@ -102,6 +102,7 @@ func main() {
 		// TODO(bwplotka): Move to customized better setup function.
 		return runner(ctx, logger)
 	}, func(err error) {
+		level.Error(logger).Log("err", fmt.Errorf("%s runner failed: %w", cmd, err))
 		cancel()
 	})
 
diff --git a/pkg/cache/cache.go b/pkg/cache/cache.go
index 3d329b8..d643d12 100644
--- a/pkg/cache/cache.go
+++ b/pkg/cache/cache.go
@@ -134,7 +134,7 @@ func (s *SQLite3Storage) IsCached(URL string) (bool, error) {
 	row := statement.QueryRow(URL)
 	if err = row.Scan(&timestamp); err != nil {
 		// If ErrNoRows then it means URL is new, so need to call Visited.
-		if err == sql.ErrNoRows {
+		if errors.Is(err, sql.ErrNoRows) {
 			return false, nil
 		}
 		return false, err
diff --git a/pkg/cache/config.go b/pkg/cache/config.go
index f901969..921b51c 100644
--- a/pkg/cache/config.go
+++ b/pkg/cache/config.go
@@ -50,10 +50,7 @@ func (c *Config) UnmarshalYAML(value *yaml.Node) error {
 	if err := value.Decode(c.cacheParser); err != nil {
 		return err
 	}
-	if err := c.load(); err != nil {
-		return err
-	}
-	return nil
+	return c.load()
 }
 
 // load validates the cache configuration from the parser and copy it
diff --git a/pkg/clilog/clilog.go b/pkg/clilog/clilog.go
index 3c3016b..fdf3868 100644
--- a/pkg/clilog/clilog.go
+++ b/pkg/clilog/clilog.go
@@ -57,7 +57,10 @@ func New(w io.Writer) log.Logger {
 }
 
 func (l logger) Log(keyvals ...interface{}) error {
-	buf := bufPool.Get().(*buf)
+	buf, ok := bufPool.Get().(*buf)
+	if !ok {
+		return errors.New("invalid buffer")
+	}
 	buf.Reset()
 	defer bufPool.Put(buf)
 
@@ -152,14 +155,17 @@ func (enc *Encoder) EncodeKeyvals(keyvals ...interface{}) error {
 	for i := 0; i < len(keyvals); i += 2 {
 		k, v := keyvals[i], keyvals[i+1]
 		err := enc.EncodeKeyval(k, v)
-		if err == ErrUnsupportedKeyType {
+
+		var marshalError *MarshalerError
+		switch {
+		case errors.Is(err, ErrUnsupportedKeyType):
 			continue
-		}
-		if _, ok := err.(*MarshalerError); ok || err == ErrUnsupportedValueType {
+		case
+			errors.As(err, &marshalError),
+			errors.Is(err, ErrUnsupportedValueType):
 			v = err
-			err = enc.EncodeKeyval(k, v)
-		}
-		if err != nil {
+			return enc.EncodeKeyval(k, v)
+		case err != nil:
 			return err
 		}
 	}
diff --git a/pkg/mdformatter/linktransformer/config.go b/pkg/mdformatter/linktransformer/config.go
index 8760583..423705f 100644
--- a/pkg/mdformatter/linktransformer/config.go
+++ b/pkg/mdformatter/linktransformer/config.go
@@ -148,14 +148,14 @@ func getGitHubRegex(pullsIssuesRe string, repoToken string) (*regexp.Regexp, int
 	client := &http.Client{}
 
 	// Check latest pull request number.
-	reqPull, err := http.NewRequest("GET", fmt.Sprintf(gitHubAPIURL, reponame, "pulls"), nil)
+	reqPull, err := http.NewRequest(http.MethodGet, fmt.Sprintf(gitHubAPIURL, reponame, "pulls"), nil)
 	if err != nil {
 		return nil, math.MaxInt64, err
 	}
 	reqPull.Header.Set("User-Agent", "mdox")
 
 	// Check latest issue number and return whichever is greater.
-	reqIssue, err := http.NewRequest("GET", fmt.Sprintf(gitHubAPIURL, reponame, "issues"), nil)
+	reqIssue, err := http.NewRequest(http.MethodGet, fmt.Sprintf(gitHubAPIURL, reponame, "issues"), nil)
 	if err != nil {
 		return nil, math.MaxInt64, err
 	}
@@ -170,7 +170,7 @@ func getGitHubRegex(pullsIssuesRe string, repoToken string) (*regexp.Regexp, int
 	if err != nil {
 		return nil, math.MaxInt64, err
 	}
-	if respPull.StatusCode != 200 {
+	if respPull.StatusCode != http.StatusOK {
 		return nil, math.MaxInt64, fmt.Errorf("pulls API request failed. status code: %d", respPull.StatusCode)
 	}
 	defer respPull.Body.Close()
@@ -182,7 +182,7 @@ func getGitHubRegex(pullsIssuesRe string, repoToken string) (*regexp.Regexp, int
 	if err != nil {
 		return nil, math.MaxInt64, err
 	}
-	if respIssue.StatusCode != 200 {
+	if respIssue.StatusCode != http.StatusOK {
 		return nil, math.MaxInt64, fmt.Errorf("issues API request failed. status code: %d", respIssue.StatusCode)
 	}
 	defer respIssue.Body.Close()
diff --git a/pkg/mdformatter/linktransformer/link.go b/pkg/mdformatter/linktransformer/link.go
index a2b842d..34a82a0 100644
--- a/pkg/mdformatter/linktransformer/link.go
+++ b/pkg/mdformatter/linktransformer/link.go
@@ -173,7 +173,7 @@ func (l *localizer) TransformDestination(ctx mdformatter.SourceContext, destinat
 	return absLinkToRelLink(newDest, ctx.Filepath)
 }
 
-func (l *localizer) Close(mdformatter.SourceContext) error { return nil }
+func (*localizer) Close(mdformatter.SourceContext) error { return nil }
 
 type validator struct {
 	logger         log.Logger
@@ -532,12 +532,12 @@ func (l localLinksCache) addRelLinks(localLink string) error {
 	reader := bufio.NewReader(file)
 	for {
 		b, err = reader.ReadBytes('\n')
-		if err != nil {
-			if err != io.EOF {
-				return fmt.Errorf("failed to read file %v: %w", localLink, err)
-			}
+		if errors.Is(err, io.EOF) {
 			break
 		}
+		if err != nil {
+			return fmt.Errorf("failed to read file %v: %w", localLink, err)
+		}
 
 		if bytes.HasPrefix(b, []byte(`#`)) {
 			ids = append(ids, toHeaderID(b))
diff --git a/pkg/mdformatter/linktransformer/link_bench_test.go b/pkg/mdformatter/linktransformer/link_bench_test.go
index 1fd26ad..8a02eca 100644
--- a/pkg/mdformatter/linktransformer/link_bench_test.go
+++ b/pkg/mdformatter/linktransformer/link_bench_test.go
@@ -34,6 +34,8 @@ This is a test section [link](./doc.md#this-is-a-section)`
 )
 
 func benchLinktransformer(b *testing.B) {
+	b.Helper()
+
 	tmpDir, err := os.MkdirTemp("", "bench-test")
 	testutil.Ok(b, err)
 	b.Cleanup(func() { testutil.Ok(b, os.RemoveAll(tmpDir)) })
diff --git a/pkg/mdformatter/linktransformer/validator.go b/pkg/mdformatter/linktransformer/validator.go
index 9787575..137c1b6 100644
--- a/pkg/mdformatter/linktransformer/validator.go
+++ b/pkg/mdformatter/linktransformer/validator.go
@@ -32,7 +32,7 @@ func (v GitHubPullsIssuesValidator) IsValid(k futureKey, r *validator) (bool, er
 }
 
 // RoundTripValidator.IsValid returns true if URL is checked by colly or it is a valid local link.
-func (v RoundTripValidator) IsValid(k futureKey, r *validator) (bool, error) {
+func (RoundTripValidator) IsValid(k futureKey, r *validator) (bool, error) {
 	matches := remoteLinkPrefixRe.FindAllStringIndex(k.dest, 1)
 	if matches == nil && r.validateConfig.ExplicitLocalValidators {
 		r.l.localLinksChecked.Inc()
@@ -73,7 +73,7 @@ func (v RoundTripValidator) IsValid(k futureKey, r *validator) (bool, error) {
 }
 
 // IgnoreValidator.IsValid returns true if matched so that link in not checked.
-func (v IgnoreValidator) IsValid(k futureKey, r *validator) (bool, error) {
+func (IgnoreValidator) IsValid(_ futureKey, r *validator) (bool, error) {
 	r.l.ignoreSkippedLinks.Inc()
 
 	return true, nil
diff --git a/pkg/mdformatter/mdformatter.go b/pkg/mdformatter/mdformatter.go
index ceabbbc..eb951fc 100644
--- a/pkg/mdformatter/mdformatter.go
+++ b/pkg/mdformatter/mdformatter.go
@@ -182,13 +182,13 @@ func FormatFrontMatter(m map[string]interface{}) ([]byte, error) {
 		keys: keys,
 	}
 
-	b := bytes.NewBuffer([]byte("---\n"))
+	b := bytes.NewBufferString("---\n")
 	o, err := yaml.Marshal(f)
 	if err != nil {
 		return nil, fmt.Errorf("marshall front matter: %w", err)
 	}
 	_, _ = b.Write(o)
-	_, _ = b.Write([]byte("---\n\n"))
+	_, _ = b.WriteString("---\n\n")
 	return b.Bytes(), nil
 }
 
diff --git a/pkg/mdformatter/mdformatter_bench_test.go b/pkg/mdformatter/mdformatter_bench_test.go
index bd99bb1..1b0c021 100644
--- a/pkg/mdformatter/mdformatter_bench_test.go
+++ b/pkg/mdformatter/mdformatter_bench_test.go
@@ -14,7 +14,9 @@ import (
 
 var testBuf bytes.Buffer
 
-func benchMdformatter(filename string, b *testing.B) {
+func benchMdformatter(b *testing.B, filename string) {
+	b.Helper()
+
 	file, err := os.OpenFile(filename, os.O_RDONLY, 0)
 	testutil.Ok(b, err)
 	defer file.Close()
@@ -28,4 +30,4 @@ func benchMdformatter(filename string, b *testing.B) {
 	})
 }
 
-func Benchmark_Mdformatter(b *testing.B) { benchMdformatter("testdata/not_formatted.md", b) }
+func Benchmark_Mdformatter(b *testing.B) { benchMdformatter(b, "testdata/not_formatted.md") }
diff --git a/pkg/mdformatter/mdgen/mdgen.go b/pkg/mdformatter/mdgen/mdgen.go
index 8baa3d0..245e45f 100644
--- a/pkg/mdformatter/mdgen/mdgen.go
+++ b/pkg/mdformatter/mdgen/mdgen.go
@@ -5,6 +5,7 @@ package mdgen
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"os/exec"
 	"strconv"
@@ -19,9 +20,7 @@ const (
 	infoStringKeyExitCode = "mdox-expect-exit-code"
 )
 
-var (
-	newLineChar = []byte("\n")
-)
+var newLineChar = []byte("\n")
 
 type genCodeBlockTransformer struct{}
 
@@ -29,7 +28,7 @@ func NewCodeBlockTransformer() *genCodeBlockTransformer {
 	return &genCodeBlockTransformer{}
 }
 
-func (t *genCodeBlockTransformer) TransformCodeBlock(ctx mdformatter.SourceContext, infoString []byte, code []byte) ([]byte, error) {
+func (*genCodeBlockTransformer) TransformCodeBlock(ctx mdformatter.SourceContext, infoString []byte, code []byte) ([]byte, error) {
 	if len(infoString) == 0 {
 		return code, nil
 	}
@@ -82,13 +81,13 @@ func (t *genCodeBlockTransformer) TransformCodeBlock(ctx mdformatter.SourceConte
 		cmd.Stdout = &b
 		if err := cmd.Run(); err != nil {
 			expectedCode, _ := strconv.Atoi(infoStringAttr[infoStringKeyExitCode])
-			if exitErr, ok := err.(*exec.ExitError); ok {
-				if exitErr.ExitCode() != expectedCode {
-					return nil, fmt.Errorf("run %v, expected exit code %v, got %v, out: %v, error: %w", execCmd, expectedCode, exitErr.ExitCode(), b.String(), err)
-				}
-			} else {
+			var exitErr *exec.ExitError
+			if !errors.As(err, &exitErr) {
 				return nil, fmt.Errorf("run %v, out: %v, error: %w", execCmd, b.String(), err)
 			}
+			if exitErr.ExitCode() != expectedCode {
+				return nil, fmt.Errorf("run %v, expected exit code %v, got %v, out: %v, error: %w", execCmd, expectedCode, exitErr.ExitCode(), b.String(), err)
+			}
 		}
 		output := b.Bytes()
 		// Add newline to output if not present.
@@ -101,4 +100,4 @@ func (t *genCodeBlockTransformer) TransformCodeBlock(ctx mdformatter.SourceConte
 	panic("should never get here")
 }
 
-func (t *genCodeBlockTransformer) Close(ctx mdformatter.SourceContext) error { return nil }
+func (*genCodeBlockTransformer) Close(_ mdformatter.SourceContext) error { return nil }
diff --git a/pkg/mdformatter/mdgen/mdgen_bench_test.go b/pkg/mdformatter/mdgen/mdgen_bench_test.go
index 5668539..611bd6d 100644
--- a/pkg/mdformatter/mdgen/mdgen_bench_test.go
+++ b/pkg/mdformatter/mdgen/mdgen_bench_test.go
@@ -15,7 +15,9 @@ import (
 
 var testBuf bytes.Buffer
 
-func benchMdgen(filename string, b *testing.B) {
+func benchMdgen(b *testing.B, filename string) {
+	b.Helper()
+
 	file, err := os.OpenFile(filename, os.O_RDONLY, 0)
 	testutil.Ok(b, err)
 	defer file.Close()
@@ -30,8 +32,8 @@ func benchMdgen(filename string, b *testing.B) {
 	})
 }
 
-func Benchmark_Mdgen_Sleep2(b *testing.B) { benchMdgen("benchdata/sleep2.md", b) }
+func Benchmark_Mdgen_Sleep2(b *testing.B) { benchMdgen(b, "benchdata/sleep2.md") }
 
-func Benchmark_Mdgen_Sleep5(b *testing.B) { benchMdgen("benchdata/sleep5.md", b) }
+func Benchmark_Mdgen_Sleep5(b *testing.B) { benchMdgen(b, "benchdata/sleep5.md") }
 
-func Benchmark_Mdgen_GoHelp(b *testing.B) { benchMdgen("benchdata/gohelp.md", b) }
+func Benchmark_Mdgen_GoHelp(b *testing.B) { benchMdgen(b, "benchdata/gohelp.md") }
diff --git a/pkg/mdformatter/transformer.go b/pkg/mdformatter/transformer.go
index 43ada32..e4bfb7e 100644
--- a/pkg/mdformatter/transformer.go
+++ b/pkg/mdformatter/transformer.go
@@ -5,6 +5,7 @@ package mdformatter
 
 import (
 	"bytes"
+	"errors"
 	"io"
 	"regexp"
 	"strconv"
@@ -102,7 +103,8 @@ func (t *transformer) Render(w io.Writer, source []byte, node ast.Node) error {
 				}
 				out += token.String()
 			}
-			if err := z.Err(); err != nil && err != io.EOF {
+
+			if err := z.Err(); err != nil && !errors.Is(err, io.EOF) {
 				return ast.WalkStop, err
 			}
 
diff --git a/pkg/transform/transform.go b/pkg/transform/transform.go
index 725f84a..20018d3 100644
--- a/pkg/transform/transform.go
+++ b/pkg/transform/transform.go
@@ -361,7 +361,7 @@ func (r *relLinkTransformer) TransformDestination(ctx mdformatter.SourceContext,
 	return []byte(newDest), nil
 }
 
-func (r *relLinkTransformer) Close(mdformatter.SourceContext) error { return nil }
+func (*relLinkTransformer) Close(mdformatter.SourceContext) error { return nil }
 
 type frontMatterTransformer struct {
 	localLinksStyle LocalLinksStyle
@@ -419,9 +419,9 @@ func (f *frontMatterTransformer) TransformFrontMatter(ctx mdformatter.SourceCont
 	return mdformatter.FormatFrontMatter(m)
 }
 
-func (f *frontMatterTransformer) Close(mdformatter.SourceContext) error { return nil }
+func (*frontMatterTransformer) Close(mdformatter.SourceContext) error { return nil }
 
-func (f *backMatterTransformer) TransformBackMatter(ctx mdformatter.SourceContext) ([]byte, error) {
+func (f *backMatterTransformer) TransformBackMatter(_ mdformatter.SourceContext) ([]byte, error) {
 	b := bytes.Buffer{}
 	if err := f.b._template.Execute(&b, struct {
 		Origin MatterOrigin
@@ -442,7 +442,7 @@ func (f *backMatterTransformer) TransformBackMatter(ctx mdformatter.SourceContex
 	return m, nil
 }
 
-func (f *backMatterTransformer) Close(mdformatter.SourceContext) error { return nil }
+func (*backMatterTransformer) Close(mdformatter.SourceContext) error { return nil }
 
 func firstMatch(absRelPath string, trs []*TransformationConfig) (*TransformationConfig, bool) {
 	for _, tr := range trs {
diff --git a/pkg/transform/transform_e2e_test.go b/pkg/transform/transform_e2e_test.go
index b7046ef..d5f400c 100644
--- a/pkg/transform/transform_e2e_test.go
+++ b/pkg/transform/transform_e2e_test.go
@@ -37,18 +37,18 @@ func TestTransform(t *testing.T) {
 		testutil.Ok(t, err)
 		testutil.Ok(t, transform.Dir(context.Background(), logger, mdox2))
 		assertDirContent(t, filepath.Join(testData, "expected", "test2"), filepath.Join(tmpDir, "test2"))
-
 	})
 	t.Run("mdox3.yaml", func(t *testing.T) {
 		mdox2, err := os.ReadFile(filepath.Join(testData, "mdox3.yaml"))
 		testutil.Ok(t, err)
 		testutil.Ok(t, transform.Dir(context.Background(), logger, mdox2))
 		assertDirContent(t, filepath.Join(testData, "expected", "test3"), filepath.Join(tmpDir, "test3"))
-
 	})
 }
 
 func assertDirContent(t *testing.T, expectedDir string, gotDir string) {
+	t.Helper()
+
 	// TODO(bwplotka): Check if some garbage was not generated too!
 	testutil.Ok(t, filepath.Walk(expectedDir, func(path string, info os.FileInfo, err error) error {
 		if err != nil {
diff --git a/scripts/copyright/copyright.go b/scripts/copyright/copyright.go
index e7c0781..9cd0013 100644
--- a/scripts/copyright/copyright.go
+++ b/scripts/copyright/copyright.go
@@ -46,7 +46,7 @@ func applyLicenseToProtoAndGo() error {
 			return err
 		}
 
-		if !strings.HasPrefix(string(b), string(license)) {
+		if !bytes.HasPrefix(b, license) {
 			log.Println("file", path, "is missing Copyright header. Adding.")
 
 			var bb bytes.Buffer