diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index f3644c9..1f70d14 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -68,6 +68,19 @@ jobs:
           done
           [[ "$failed" -eq 0 ]]
 
+  behaviour:
+    name: forbidden-license matching
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+
+      # Schema and shellcheck prove the run blocks parse; this proves the one
+      # that decides pass/fail actually decides it correctly.
+      - name: Forbidden-license matching
+        run: bash test/forbidden-matching_test.sh
+
   workflow:
     name: actionlint
     runs-on: ubuntu-latest
diff --git a/go-license-validator/README.md b/go-license-validator/README.md
index 1d33fdc..f9795bf 100644
--- a/go-license-validator/README.md
+++ b/go-license-validator/README.md
@@ -34,6 +34,24 @@ The action runs through multiple focused steps:
 | `fail_on_forbidden` | Whether to fail the action when forbidden licenses are found | No | `true` |
 | `include_dev_dependencies` | Include development dependencies in the scan | No | `false` |
 
+
+### How `forbidden_licenses` is matched
+
+Each entry names a **license family**, matched case-insensitively against every
+identifier in a dependency's SPDX expression:
+
+- `GPL` matches `GPL-3.0-only`, `GPL-2.0-or-later`, `GPL-3.0` — an entry matches
+  an identifier that equals it, or that continues it after `-`, `.` or `+`.
+- `GPL` does **not** match `LGPL-3.0` or `AGPL-3.0`. Those are different
+  licenses that merely contain the same letters; list them separately if you
+  want them blocked (`GPL;LGPL;AGPL`).
+- Composite expressions are split on `AND` / `OR` / `WITH` and parentheses, so
+  `Apache-2.0 AND GPL-2.0` is caught by `GPL`, as is
+  `GPL-2.0-or-later WITH GCC-exception-3.1`.
+
+An entry naming a full identifier (`GPL-3.0`) still works, and also matches the
+modern `-only` / `-or-later` spellings that identifier predates.
+
 ## Outputs
 
 | Output | Description |
diff --git a/go-license-validator/action.yml b/go-license-validator/action.yml
index 7a53b0d..5624e65 100644
--- a/go-license-validator/action.yml
+++ b/go-license-validator/action.yml
@@ -129,7 +129,28 @@ runs:
             forbidden=$(echo "$forbidden" | xargs) # Trim whitespace
             if [[ -n "$forbidden" ]]; then
               # Check if this forbidden license exists in our found licenses
-              if echo "$LICENSES_FOUND" | jq -e --arg license "$forbidden" 'index($license) != null' >/dev/null 2>&1; then
+              # A found value is an SPDX *expression*, not a bare identifier:
+              # it may combine identifiers with AND / OR / WITH and parens, so
+              # it is split into identifiers before matching. A forbidden entry
+              # names a family — "GPL" must catch "GPL-3.0-only" while leaving
+              # "LGPL-3.0" and "AGPL-3.0" alone, since those are different
+              # licenses that merely contain the same letters. Hence equality
+              # or the entry followed by an SPDX separator, never a bare
+              # substring. (Add "LGPL" explicitly if you want it blocked.)
+              if echo "$LICENSES_FOUND" | jq -e --arg forbidden "$forbidden" '
+                def identifiers:
+                  [ splits("[[:space:]()]+") ]
+                  | map(select(. != ""))
+                  | map(select(ascii_downcase as $t | ["and", "or", "with"] | index($t) | not));
+                def blocked($entry):
+                  (ascii_downcase) as $l
+                  | ($entry | ascii_downcase) as $f
+                  | $l == $f
+                    or ($l | startswith($f + "-"))
+                    or ($l | startswith($f + "."))
+                    or ($l | startswith($f + "+"));
+                any(.[]; identifiers | any(blocked($forbidden)))
+              ' >/dev/null 2>&1; then
                 FORBIDDEN_FOUND=true
                 if [[ -n "$FORBIDDEN_DETAILS" ]]; then
                   FORBIDDEN_DETAILS="$FORBIDDEN_DETAILS, $forbidden"
diff --git a/npm-license-validator/README.md b/npm-license-validator/README.md
index a76dda8..e9c5a59 100644
--- a/npm-license-validator/README.md
+++ b/npm-license-validator/README.md
@@ -34,6 +34,24 @@ The action runs through multiple focused steps:
 | `fail_on_forbidden` | Whether to fail the action when forbidden licenses are found | No | `true` |
 | `include_dev_dependencies` | Include development dependencies in the scan | No | `false` |
 
+
+### How `forbidden_licenses` is matched
+
+Each entry names a **license family**, matched case-insensitively against every
+identifier in a dependency's SPDX expression:
+
+- `GPL` matches `GPL-3.0-only`, `GPL-2.0-or-later`, `GPL-3.0` — an entry matches
+  an identifier that equals it, or that continues it after `-`, `.` or `+`.
+- `GPL` does **not** match `LGPL-3.0` or `AGPL-3.0`. Those are different
+  licenses that merely contain the same letters; list them separately if you
+  want them blocked (`GPL;LGPL;AGPL`).
+- Composite expressions are split on `AND` / `OR` / `WITH` and parentheses, so
+  `Apache-2.0 AND GPL-2.0` is caught by `GPL`, as is
+  `GPL-2.0-or-later WITH GCC-exception-3.1`.
+
+An entry naming a full identifier (`GPL-3.0`) still works, and also matches the
+modern `-only` / `-or-later` spellings that identifier predates.
+
 ## Outputs
 
 | Output | Description |
diff --git a/npm-license-validator/action.yml b/npm-license-validator/action.yml
index 9a391c7..61df7cc 100644
--- a/npm-license-validator/action.yml
+++ b/npm-license-validator/action.yml
@@ -132,7 +132,28 @@ runs:
           for forbidden in "${FORBIDDEN_ARRAY[@]}"; do
             forbidden=$(echo "$forbidden" | xargs)
             if [[ -n "$forbidden" ]]; then
-              if echo "$LICENSES_FOUND" | jq -e --arg license "$forbidden" 'index($license) != null' >/dev/null 2>&1; then
+              # A found value is an SPDX *expression*, not a bare identifier:
+              # it may combine identifiers with AND / OR / WITH and parens, so
+              # it is split into identifiers before matching. A forbidden entry
+              # names a family — "GPL" must catch "GPL-3.0-only" while leaving
+              # "LGPL-3.0" and "AGPL-3.0" alone, since those are different
+              # licenses that merely contain the same letters. Hence equality
+              # or the entry followed by an SPDX separator, never a bare
+              # substring. (Add "LGPL" explicitly if you want it blocked.)
+              if echo "$LICENSES_FOUND" | jq -e --arg forbidden "$forbidden" '
+                def identifiers:
+                  [ splits("[[:space:]()]+") ]
+                  | map(select(. != ""))
+                  | map(select(ascii_downcase as $t | ["and", "or", "with"] | index($t) | not));
+                def blocked($entry):
+                  (ascii_downcase) as $l
+                  | ($entry | ascii_downcase) as $f
+                  | $l == $f
+                    or ($l | startswith($f + "-"))
+                    or ($l | startswith($f + "."))
+                    or ($l | startswith($f + "+"));
+                any(.[]; identifiers | any(blocked($forbidden)))
+              ' >/dev/null 2>&1; then
                 FORBIDDEN_FOUND=true
                 if [[ -n "$FORBIDDEN_DETAILS" ]]; then
                   FORBIDDEN_DETAILS="$FORBIDDEN_DETAILS, $forbidden"
diff --git a/test/forbidden-matching_test.sh b/test/forbidden-matching_test.sh
new file mode 100755
index 0000000..af07924
--- /dev/null
+++ b/test/forbidden-matching_test.sh
@@ -0,0 +1,104 @@
+#!/usr/bin/env bash
+# Exercises the forbidden-license matching in both validators.
+#
+# The block under test is extracted from the shipped action.yml rather than
+# restated here: a copy would keep passing after the action it claims to cover
+# had changed. Extraction means this test fails loudly if the block is renamed
+# or reshaped, which is the correct outcome — it can no longer prove anything.
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+work="$(mktemp -d)"
+trap 'rm -rf "$work"' EXIT
+
+pass=0
+fail=0
+
+# extract_block pulls the matching loop out of an action.yml and de-indents it
+# to column 0 so it can be sourced as a standalone script.
+extract_block() {
+  local action="$1" out="$2"
+  python3 - "$action" "$out" <<'PY'
+import sys
+
+action, out = sys.argv[1], sys.argv[2]
+s = open(action).read()
+start = s.index('        if [[ "$LICENSES_FOUND" != "[]"')
+end = s.index('        echo "forbidden_found=', start)
+block = s[start:end]
+block = "\n".join(l[8:] if l.startswith("        ") else l for l in block.split("\n"))
+open(out, "w").write(block)
+PY
+}
+
+# run_case evaluates the extracted block for one (found, forbidden) pair and
+# echoes the two outputs the action derives from it.
+#
+# The variables below look unused here because the block that reads and writes
+# them is sourced at runtime, so shellcheck cannot see the use.
+# shellcheck disable=SC2034
+run_case() {
+  local block="$1"
+  LICENSES_FOUND="$2"
+  FORBIDDEN_LICENSES="$3"
+  local FORBIDDEN_ARRAY FORBIDDEN_FOUND FORBIDDEN_DETAILS FORBIDDEN_LIST
+  IFS=';' read -ra FORBIDDEN_ARRAY <<< "$FORBIDDEN_LICENSES"
+  FORBIDDEN_FOUND=false
+  FORBIDDEN_DETAILS=""
+  FORBIDDEN_LIST=""
+  # shellcheck source=/dev/null
+  source "$block"
+  echo "$FORBIDDEN_FOUND|$FORBIDDEN_DETAILS"
+}
+
+check() { # block desc found forbidden want_found want_details
+  local block="$1" desc="$2" got
+  got="$(run_case "$block" "$3" "$4")"
+  if [[ "$got" == "$5|$6" ]]; then
+    pass=$((pass + 1))
+    echo "  PASS  $desc"
+  else
+    fail=$((fail + 1))
+    echo "  FAIL  $desc -> got '$got', want '$5|$6'"
+  fi
+}
+
+for action in go-license-validator npm-license-validator; do
+  echo "== $action"
+  block="$work/$action.sh"
+  mkdir -p "$(dirname "$block")"
+  extract_block "$repo_root/$action/action.yml" "$block"
+
+  # SPDX identifiers carry a version suffix, so a family entry has to match the
+  # whole family. This is the case the exact-match implementation missed: with
+  # FORBIDDEN_LICENSES="GPL;AGPL" it blocked only a license literally named
+  # "GPL", which no real dependency is.
+  check "$block" "GPL-3.0-only is caught by GPL" '["GPL-3.0-only"]' 'GPL;AGPL' true 'GPL'
+  check "$block" "AGPL-3.0 is caught by AGPL" '["AGPL-3.0"]' 'GPL;AGPL' true 'AGPL'
+
+  # Different licenses that merely contain the same letters must not be caught
+  # by a family entry — a project blocking GPL has not thereby blocked LGPL.
+  check "$block" "AGPL-3.0 is not caught by GPL" '["AGPL-3.0"]' 'GPL' false ''
+  check "$block" "LGPL is not caught by GPL" '["LGPL-3.0-or-later"]' 'GPL;AGPL' false ''
+  check "$block" "LGPL is caught when listed" '["LGPL-3.0-or-later"]' 'LGPL' true 'LGPL'
+
+  # A found value is an SPDX expression; a forbidden identifier inside a
+  # composite is still present in the dependency tree.
+  check "$block" "composite AND is split" '["Apache-2.0 AND GPL-2.0"]' 'GPL' true 'GPL'
+  check "$block" "composite OR is split" '["BSD-3-Clause OR GPL-2.0-or-later"]' 'GPL' true 'GPL'
+  check "$block" "WITH exception matches the base" '["GPL-2.0-or-later WITH GCC-exception-3.1"]' 'GPL' true 'GPL'
+
+  # The identifiers the README documents must keep working, including against
+  # the modern -only / -or-later spellings they predate.
+  check "$block" "exact documented id works" '["GPL-3.0"]' 'GPL-3.0' true 'GPL-3.0'
+  check "$block" "documented id matches -only form" '["GPL-3.0-only"]' 'GPL-3.0' true 'GPL-3.0'
+
+  check "$block" "permissive set passes" '["MIT","Apache-2.0","BSD-3-Clause"]' 'GPL;AGPL' false ''
+  check "$block" "empty found list passes" '[]' 'GPL;AGPL' false ''
+  check "$block" "matching is case-insensitive" '["gpl-3.0-only"]' 'GPL' true 'GPL'
+  check "$block" "every matched family is reported" '["GPL-2.0","AGPL-3.0"]' 'GPL;AGPL' true 'GPL, AGPL'
+done
+
+echo
+echo "passed=$pass failed=$fail"
+[[ "$fail" -eq 0 ]]