diff --git a/.gitignore b/.gitignore
index 2ef777e..198945c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
+/.upkg
 /results.tap
diff --git a/README.md b/README.md
index f147134..bfd7113 100644
--- a/README.md
+++ b/README.md
@@ -6,22 +6,31 @@ you need the container image tag variant.
 
 ## Behavior
 
-| git ref                                                        | program version |
-| -------------------------------------------------------------- | --------------- |
-| `refs/heads/main`                                              | `main`          |
-| `refs/heads/master`                                            | `master`        |
-| `refs/heads/ft-refactor`                                       | `ft-refactor`   |
-| `refs/tags/v1.0.3`                                             | `v1.0.3`        |
-| `refs/tags/1.0.3`                                              | `v1.0.3`        |
-| `refs/tags/very-pinned` (treated just like branches)           | `very-pinned`   |
-| `refs/tags/f1.0.3` (treated just like branches)                | `f1.0.3`        |
-| `refs/tags/v`                                                  | `v`             |
-| `e02d09699ffb56440f34cb7448a0bc436e3ae212` (i.e. non-symbolic) | `e02d0969`      |
-| `e02d09699ffb56440f34cb7448` (not 40 hex chars)                | error           |
-| `master` (no `refs/heads/` prefix)                             | error           |
-| `v1.0.3` (no `refs/tags/` prefix)                              | error           |
-| `refs/heads/` (empty branch name)                              | error           |
-| `refs/tags/` (empty tag name)                                  | error           |
+| git ref                                                        | program version      | prefix     |
+| -------------------------------------------------------------- | -------------------- | ---------- |
+| `refs/heads/main`                                              | `main`               | `v`        |
+| `refs/heads/master`                                            | `master`             | `v`        |
+| `refs/heads/ft-refactor`                                       | `ft-refactor`        | `v`        |
+| `refs/tags/v1.0.3`                                             | `v1.0.3`             | `v`        |
+| `refs/tags/1.0.3`                                              | `1.0.3`              | `v`        |
+| `refs/tags/very-pinned` (treated just like branches)           | `very-pinned`        | `v`        |
+| `refs/tags/f1.0.3` (treated just like branches)                | `f1.0.3`             | `v`        |
+| `refs/tags/v`                                                  | `v`                  | `v`        |
+| `e02d09699ffb56440f34cb7448a0bc436e3ae212` (i.e. non-symbolic) | `e02d0969`           | `v`        |
+| `e02d09699ffb56440f34cb7448` (not 40 hex chars)                | error                | `v`        |
+| `master` (no `refs/heads/` prefix)                             | error                | `v`        |
+| `v1.0.3` (no `refs/tags/` prefix)                              | error                | `v`        |
+| `refs/heads/` (empty branch name)                              | error                | `v`        |
+| `refs/tags/` (empty tag name)                                  | error                | `v`        |
+| **Custom prefix**                                              |                      |            |
+| `refs/heads/main`                                              | `main`               | `mytool-v` |
+| `refs/heads/mytool-vmain`                                      | `mytool-vmain`       | `mytool-v` |
+| `refs/tags/v1.0.3`                                             | `v1.0.3`             | `mytool-v` |
+| `refs/tags/mytool-v1.0.3`                                      | `v1.0.3`             | `mytool-v` |
+| `refs/tags/mytool-v1.0.3` (prefix=`v`)                         | `mytool-v1.0.3`      | `v`        |
+| `refs/tags/1.0.3`                                              | `1.0.3`              | `mytool-v` |
+| `refs/tags/mytool-very-pinned` (treated just like branches)    | `mytool-very-pinned` | `mytool-v` |
+| `refs/tags/mytool-v`                                           | `mytool-v`           | `mytool-v` |
 
 ## CLI
 
@@ -48,8 +57,21 @@ version=$(program-version "$(jq -re '.version // empty' "$PKGROOT/upkg.json" 2>/
 
 ### Parameters
 
-- `ref`: The git ref to calculate the version from, defaults to
-  `${{ github.ref }}`.
+- `ref`: The git ref to calculate the version from. Defaults to `${{ github.ref }}`.
+- `prefix`: Operate on tag versions with the specified prefix. Defaults to `v`.
+
+### Inputs
+
+| Name     | Description                                        | Default                  |
+| -------- | -------------------------------------------------- | ------------------------ |
+| `ref`    | The git ref to calculate the version from.         | `${{ github.ref }} input |
+| `prefix` | Operate on tag versions with the specified prefix. | `v`                      |
+
+### Outputs
+
+| Name      | Description          |
+| --------- | -------------------- |
+| `version` | The program version. |
 
 ### Usage
 
diff --git a/action.yaml b/action.yaml
index dc79c9a..f609cea 100644
--- a/action.yaml
+++ b/action.yaml
@@ -5,6 +5,10 @@ inputs:
     description: The git ref to use. Defaults to `github.ref`.
     default: ${{ github.ref }}
     required: false
+  prefix:
+    description: Operate on tag versions with the specified prefix. Defaults to `v``.
+    default: ${{ github.ref }}
+    required: false
 outputs:
   version:
     description: The program version
diff --git a/bin/program-version b/bin/program-version
index ae870f8..dad6663 100755
--- a/bin/program-version
+++ b/bin/program-version
@@ -1,20 +1,47 @@
 #!/usr/bin/env bash
+# shellcheck source-path=..
 
 main() {
   set -eo pipefail; shopt -s inherit_errexit
+  local pkgroot; pkgroot=$(realpath "$(dirname "$(realpath "${BASH_SOURCE[0]}")")/..")
+  source "$pkgroot/.upkg/records.sh/records.sh"
+  DOC="program-version - Determine the program version based on a git ref.
+Usage:
+  program-version [-p P] REF
 
-  local ref=${1:?'Usage: program-version REF'}
-  if [[ $ref =~ refs/tags/v?[0-9]+ ]]; then
-    local tag=${ref#'refs/tags/'}
-    printf "v%s\n" "${tag#v}"
-  elif [[ $ref = refs/tags/* ]]; then
-    printf "%s\n" "${ref#'refs/tags/'}"
-  elif [[ $ref = refs/heads/?* ]]; then
-    printf "%s\n" "${ref#'refs/heads/'}"
-  elif [[ $ref =~ ^[0-9a-f]{40}$ ]]; then
-    printf "%s\n" "${ref:0:8}"
+Options:
+  -p --prefix P  Operate on tag versions with the specified prefix [default: v]
+"
+# docopt parser below, refresh this parser with `docopt.sh program-version`
+# shellcheck disable=2016,2086,2317,1090,1091,2034
+docopt() { local v='2.0.2'; source \
+"$pkgroot/.upkg/docopt-lib-v$v/docopt-lib.sh" "$v" || { ret=$?;printf -- "exit \
+%d\n" "$ret";exit "$ret";};set -e;trimmed_doc=${DOC:0:193};usage=${DOC:68:35}
+digest=a75bc;options=('-p --prefix 1');node_0(){ value __prefix 0;};node_1(){
+value REF a;};node_2(){ optional 0;};node_3(){ sequence 2 1;};cat <<<' \
+docopt_exit() { [[ -n $1 ]] && printf "%s\n" "$1" >&2;printf "%s\n" \
+"${DOC:68:35}" >&2;exit 1;}';local varnames=(__prefix REF) varname;for varname \
+in "${varnames[@]}"; do unset "var_$varname";done;parse 3 "$@";local \
+p=${DOCOPT_PREFIX:-''};for varname in "${varnames[@]}"; do unset "$p$varname"
+done;eval $p'__prefix=${var___prefix:-v};'$p'REF=${var_REF:-};';local docopt_i=1
+[[ $BASH_VERSION =~ ^4.3 ]] && docopt_i=2;for ((;docopt_i>0;docopt_i--)); do
+for varname in "${varnames[@]}"; do declare -p "$p$varname";done;done;}
+# docopt parser above, complete command for generating this parser is `docopt.sh --library='"$pkgroot/.upkg/docopt-lib-v$v/docopt-lib.sh"' program-version`
+  eval "$(docopt "$@")"
+
+  # shellcheck disable=2154
+  local P=$__prefix
+
+  if [[ $REF = refs/tags/${P}* && ${REF#"refs/tags/$P"} =~ ^[0-9]+\.[0-9]+\.[0-9]+ ]]; then
+    printf "v%s\n" "${REF#"refs/tags/$P"}"
+  elif [[ $REF = refs/tags/* ]]; then
+    printf "%s\n" "${REF#'refs/tags/'}"
+  elif [[ $REF = refs/heads/?* ]]; then
+    printf "%s\n" "${REF#'refs/heads/'}"
+  elif [[ $REF =~ ^[0-9a-f]{40}$ ]]; then
+    printf "%s\n" "${REF:0:8}"
   else
-    printf "program-version.sh: REF must start with refs/tags/, refs/heads/, or be a shasum. Got '%s'.\n" "$ref" >&2
+    error "REF must start with refs/tags/, refs/heads/, or be a shasum. Got '%s'.\n" "$REF" >&2
     return 1
   fi
 }
diff --git a/test.bats b/test.bats
index 400ed3a..438496a 100755
--- a/test.bats
+++ b/test.bats
@@ -25,9 +25,9 @@ setup_file() {
   [ "$output" = "v1.0.3" ]
 }
 
-@test 'refs/tags/1.0.3=v1.0.3' {
+@test 'refs/tags/1.0.3=1.0.3' {
   run bin/program-version refs/tags/1.0.3
-  [ "$output" = "v1.0.3" ]
+  [ "$output" = "1.0.3" ]
 }
 
 @test 'refs/tags/very-pinned=very-pinned' {
@@ -69,3 +69,43 @@ setup_file() {
 @test 'refs/tags=error' {
   run -1 bin/program-version refs/tags
 }
+
+@test '-p=mytool-v refs/heads/main=main' {
+  run bin/program-version -p mytool-v refs/heads/main
+  [ "$output" = "main" ]
+}
+
+@test '-p=mytool-v refs/heads/mytool-vmain=mytool-vmain' {
+  run bin/program-version -p mytool-v refs/heads/mytool-vmain
+  [ "$output" = "mytool-vmain" ]
+}
+
+@test '-p=mytool-v refs/tags/v1.0.3=v1.0.3' {
+  run bin/program-version -p mytool-v refs/tags/v1.0.3
+  [ "$output" = "v1.0.3" ]
+}
+
+@test '-p=mytool-v refs/tags/mytool-v1.0.3=v1.0.3' {
+  run bin/program-version -p mytool-v refs/tags/mytool-v1.0.3
+  [ "$output" = "v1.0.3" ]
+}
+
+@test '-p=mytool-v refs/tags/mytool-v1.0.3=mytool-v1.0.3' {
+  run bin/program-version -p v refs/tags/mytool-v1.0.3
+  [ "$output" = "mytool-v1.0.3" ]
+}
+
+@test '-p=mytool-v refs/tags/1.0.3=1.0.3' {
+  run bin/program-version -p mytool-v refs/tags/1.0.3
+  [ "$output" = "1.0.3" ]
+}
+
+@test '-p=mytool-v refs/tags/mytool-very-pinned=mytool-very-pinned' {
+  run bin/program-version -p mytool-v refs/tags/mytool-very-pinned
+  [ "$output" = "mytool-very-pinned" ]
+}
+
+@test '-p=mytool-v refs/tags/mytool-v=mytool-v' {
+  run bin/program-version -p mytool-v refs/tags/mytool-v
+  [ "$output" = "mytool-v" ]
+}
diff --git a/upkg.json b/upkg.json
index 98ddb9e..45340ff 100644
--- a/upkg.json
+++ b/upkg.json
@@ -1,3 +1,14 @@
 {
-  "name": "program-version"
+  "name": "program-version",
+  "dependencies": [
+    {
+      "tar": "https://github.com/orbit-online/records.sh/releases/download/v0.9.6/records.sh.tar.gz",
+      "sha256": "9ef37448a3c35e64c1bcddeb6e42ba7650b3dfa4e2dc457c2f82364d4b6d343d"
+    },
+    {
+      "name": "docopt-lib-v2.0.2",
+      "tar": "https://github.com/andsens/docopt.sh/releases/download/v2.0.2/docopt-lib.sh.tar.gz",
+      "sha256": "d6997858e7f2470aa602fdd1e443d89b4e2084245b485e4b7924b0f388ec401e"
+    }
+  ]
 }