diff --git a/cmd/migrate-document-versions-markdown/main.go b/cmd/migrate-document-versions-markdown/main.go
new file mode 100644
index 000000000..83e91add3
--- /dev/null
+++ b/cmd/migrate-document-versions-markdown/main.go
@@ -0,0 +1,180 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+// Command migrate-document-versions-markdown rewrites document_versions.content
+// from legacy markdown to ProseMirror JSON (see pkg/coredata/document_version.go).
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+	"go.gearno.de/kit/pg"
+	"go.probo.inc/probo/pkg/coredata"
+	"go.probo.inc/probo/pkg/gid"
+	"go.probo.inc/probo/pkg/prosemirror"
+)
+
+func main() {
+	if err := run(); err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+}
+
+func run() error {
+	var (
+		pgDSN            string
+		dryRun           bool
+		continueOnError  bool
+	)
+
+	flag.StringVar(
+		&pgDSN,
+		"pg-dsn",
+		os.Getenv("DATABASE_URL"),
+		"PostgreSQL connection URL (default: DATABASE_URL env)",
+	)
+	flag.BoolVar(&dryRun, "dry-run", false, "list rows that would be migrated without writing")
+	flag.BoolVar(
+		&continueOnError,
+		"continue-on-error",
+		false,
+		"keep going when a row fails; exit non-zero if any failed",
+	)
+	flag.Parse()
+
+	if pgDSN == "" {
+		return fmt.Errorf("set -pg-dsn or DATABASE_URL")
+	}
+
+	ctx := context.Background()
+
+	pool, err := pgxpool.New(ctx, pgDSN)
+	if err != nil {
+		return fmt.Errorf("cannot connect to database: %w", err)
+	}
+	defer pool.Close()
+
+	rows, err := pool.Query(
+		ctx,
+		`
+SELECT id::text
+FROM document_versions
+WHERE content IS NOT NULL
+	AND btrim(content) <> ''
+ORDER BY id;
+`,
+	)
+	if err != nil {
+		return fmt.Errorf("cannot list document versions: %w", err)
+	}
+	defer rows.Close()
+
+	var ids []string
+	for rows.Next() {
+		var id string
+		if err := rows.Scan(&id); err != nil {
+			return fmt.Errorf("cannot scan document version id: %w", err)
+		}
+		ids = append(ids, id)
+	}
+	if err := rows.Err(); err != nil {
+		return fmt.Errorf("cannot iterate document versions: %w", err)
+	}
+
+	conn, err := pool.Acquire(ctx)
+	if err != nil {
+		return fmt.Errorf("cannot acquire connection: %w", err)
+	}
+	defer conn.Release()
+
+	pgxConn := conn.Conn()
+
+	var failures int
+	for _, idStr := range ids {
+		if err := migrateOne(ctx, pgxConn, idStr, dryRun); err != nil {
+			fmt.Fprintf(os.Stderr, "%v\n", err)
+			failures++
+			if !continueOnError {
+				return fmt.Errorf("stopped after %d failure(s)", failures)
+			}
+			continue
+		}
+	}
+
+	if failures > 0 {
+		return fmt.Errorf("%d row(s) failed", failures)
+	}
+
+	fmt.Println("done")
+	return nil
+}
+
+func migrateOne(ctx context.Context, conn pg.Conn, idStr string, dryRun bool) error {
+	versionID, err := gid.ParseGID(idStr)
+	if err != nil {
+		return fmt.Errorf("invalid document version id %q: %w", idStr, err)
+	}
+
+	dv := &coredata.DocumentVersion{}
+	if err := dv.LoadByID(ctx, conn, coredata.NewNoScope(), versionID); err != nil {
+		return fmt.Errorf("cannot load document version %q: %w", idStr, err)
+	}
+
+	if isProseMirrorDocJSON(dv.Content) {
+		fmt.Printf("skip %s (already ProseMirror doc JSON)\n", idStr)
+		return nil
+	}
+
+	if dryRun {
+		fmt.Printf("would migrate %s\n", idStr)
+		return nil
+	}
+
+	doc, err := prosemirror.ParseMarkdown(dv.Content)
+	if err != nil {
+		return fmt.Errorf("cannot parse markdown for %q: %w", idStr, err)
+	}
+
+	out, err := json.Marshal(doc)
+	if err != nil {
+		return fmt.Errorf("cannot marshal prosemirror for %q: %w", idStr, err)
+	}
+
+	dv.Content = string(out)
+	dv.UpdatedAt = time.Now()
+
+	if err := dv.Update(ctx, conn, coredata.NewNoScope()); err != nil {
+		return fmt.Errorf("cannot update document version %q: %w", idStr, err)
+	}
+
+	fmt.Printf("updated %s\n", idStr)
+	return nil
+}
+
+func isProseMirrorDocJSON(s string) bool {
+	var probe struct {
+		Type string `json:"type"`
+	}
+	if err := json.Unmarshal([]byte(s), &probe); err != nil {
+		return false
+	}
+	return probe.Type == "doc"
+}