diff --git a/test/migrate-cid/main.go b/test/migrate-cid/main.go
new file mode 100644
index 000000000..e3f9507c2
--- /dev/null
+++ b/test/migrate-cid/main.go
@@ -0,0 +1,102 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"io/ioutil"
+	"log"
+	"os"
+	"strings"
+
+	cid "github.com/ipfs/go-cid"
+)
+
+// Command to parse a file and replace CIDv0 with CIDv1 strings.
+// Single argument: the path to the file where the in-place replace will happen.
+
+// These are hardcoded in `cid.Decode()`.
+const CID_V0_PREFIX = "Qm"
+const CID_V0_LENGTH = 46
+
+func main() {
+	if len(os.Args) < 2 {
+		log.Fatal("Missing argument with file path to replace CIDs.")
+	}
+	replaceFile := os.Args[1]
+
+	input, err := ioutil.ReadFile(replaceFile)
+	if err != nil {
+		log.Fatal(err)
+	}
+	scanner := bufio.NewScanner(bytes.NewReader(input))
+
+	outputFile, err := os.OpenFile(replaceFile, os.O_WRONLY|os.O_TRUNC, 0)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer outputFile.Close()
+
+	cidsFound := make([]cid.Cid, 0)
+	cidsReplaceCount := 0
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		// Find and store any CIDv0 in the current line.
+		cidsFound = []cid.Cid{}
+		var advanceLine int
+		for {
+			if c := findCidV0(line); c != cid.Undef {
+				cidsFound = append(cidsFound, c)
+				advanceLine = CID_V0_LENGTH
+			} else {
+				advanceLine = len(CID_V0_PREFIX)
+			}
+			if len(line) >= advanceLine {
+				line = line[advanceLine:]
+			} else {
+				break
+			}
+		}
+
+		// Start again from the start to actually replace the CID strings.
+		// (Find and replace decoupled for readability. Performance is not a
+		//  concern here.)
+		line = scanner.Text()
+		for _, cidV0 := range cidsFound {
+			cidV1 := cid.NewCidV1(cid.DagProtobuf, cidV0.Hash())
+			line = strings.Replace(line, cidV0.String(), cidV1.String(), -1)
+		}
+		outputFile.WriteString(line + "\n")
+		cidsReplaceCount += len(cidsFound) // ignoring CIDs repeated in same string (rare)
+	}
+
+	if err := scanner.Err(); err != nil {
+		log.Fatal(err)
+	}
+	log.Printf("Found and replaced %d CIDv0 strings.", cidsReplaceCount)
+}
+
+// Find first CIDv0 in string.
+func findCidV0(s string) cid.Cid {
+	cidStart := strings.Index(s, CID_V0_PREFIX)
+	if cidStart == -1 {
+		return cid.Undef
+	}
+
+	cidEnd := cidStart + CID_V0_LENGTH
+	if cidEnd > len(s) {
+		return cid.Undef
+	}
+
+	c, err := cid.Decode(s[cidStart:cidEnd])
+	if err != nil {
+		return cid.Undef
+	}
+
+	// This shouldn't happen but just in case check that the version is actually 0.
+	if c.Version() != 0 {
+		return cid.Undef
+	}
+
+	return c
+}