diff --git a/README.md b/README.md
index d0b5f5c..5d30eaf 100644
--- a/README.md
+++ b/README.md
@@ -124,8 +124,9 @@ Using these rules, everyone can build their own copy of Bantam from scratch in l
 2. Append the assistant's response message object to `messages`. If non-streaming and response has reasoning tokens (`reasoning_content` or `reasoning`), output them wrapped in `--- reasoning start ---` / `--- reasoning end ---` markers.
 3. If there are pending `tool_calls` in the assistant response:
    - For each tool call, output a trace log (`[tool call: name(args)]`).
-   - Validate JSON arguments. If invalid, format a tool-error response so the LLM can self-correct.
+   - Sanitize tool arguments to filter out non-printable and space-like Unicode characters (protecting against indirect prompt injection), and validate JSON arguments. If invalid, format a tool-error response so the LLM can self-correct.
    - Execute tool action (`shell_exec` or `run_subagent`).
+   - Sanitize the tool result output to strip any non-printable and space-like Unicode characters (leaving only ASCII space, tab, newline, and printable Unicode characters).
    - Output a trace log of the result (`[tool result: name]`).
    - Append tool result message (`role: "tool"`, `tool_call_id`, `content`: result string) to `messages`.
    - Loop back to step 1.
@@ -173,6 +174,7 @@ MicroBantam (`mb`) is a compressed Perl 5 reference implementation of the same a
 ### Features
 
 - Full agentic loop: LLM calls, `shell_exec` / `run_subagent` tool execution with JSON argument validation (invalid args are fed back so the model can self-correct), and the 5-level subagent recursion depth limit
+- Indirect prompt injection defense: sanitizes tool parameters and tool outputs by filtering non-printable and space-like Unicode characters, preserving standard space, tab, newline, and printable Unicode characters
 - A `...requesting...` in-flight indicator: in-place on a TTY (`\r` overwrite, erased on completion), a plain line when output is piped
 - Session management: `/save`, `/list`, `/load <id>` (exact id only, no prefix matching), `/cfg <param> [val]`, and auto-save to `~/.bantam/sessions/autosave.json` after every turn and on exit; session ids get `-1`, `-2`, ... suffixes on same-second collisions
 - Interactive mode (`/quit`, `/clear`, `/save`, `/list`, `/load <id>`, `/cfg`, `/help`) and file input mode
diff --git a/main.go b/main.go
index 2a36a11..958e4fd 100644
--- a/main.go
+++ b/main.go
@@ -22,6 +22,7 @@ import (
   "strconv"
   "strings"
   "time"
+  "unicode"
   "unicode/utf8"
 )
 
@@ -712,11 +713,27 @@ func cleanMessagesForLLM(msgs []Message) []Message {
   return out
 }
 
+func filterText(s string) string {
+  var b strings.Builder
+  b.Grow(len(s))
+  for _, r := range s {
+    if r == ' ' || r == '\t' || r == '\n' {
+      b.WriteRune(r)
+    } else if unicode.Is(unicode.Z, r) || unicode.IsControl(r) || unicode.Is(unicode.C, r) {
+      continue
+    } else if unicode.IsPrint(r) {
+      b.WriteRune(r)
+    }
+  }
+  return b.String()
+}
+
 func sanitizeMessages(msgs []Message) {
   for i := range msgs {
     if msgs[i].Role == "assistant" && len(msgs[i].ToolCalls) > 0 {
       for j := range msgs[i].ToolCalls {
         tc := &msgs[i].ToolCalls[j]
+        tc.Function.Arguments = filterText(tc.Function.Arguments)
         astr := tc.Function.Arguments
         var a map[string]any
         if err := json.Unmarshal([]byte(astr), &a); err != nil || a == nil {
@@ -724,6 +741,8 @@ func sanitizeMessages(msgs []Message) {
           tc.Function.Arguments = string(fixed)
         }
       }
+    } else if msgs[i].Role == "tool" && msgs[i].Content != nil {
+      msgs[i].Content = strp(filterText(*msgs[i].Content))
     }
   }
 }
@@ -956,12 +975,13 @@ func parseStream(ctx context.Context, r io.Reader) (Message, Usage, error) {
 }
 
 func shell(ctx context.Context, cmd string, timeout int) string {
+  cmd = filterText(cmd)
   cmdCtx, cancel := context.WithTimeout(ctx, time.Duration(timeout)*time.Second)
   defer cancel()
   c := exec.CommandContext(cmdCtx, "sh", "-c", cmd)
   c.WaitDelay = 100 * time.Millisecond
   out, err := c.CombinedOutput()
-  res := strings.TrimSpace(string(out))
+  res := strings.TrimSpace(filterText(string(out)))
   if ctx.Err() != nil {
     return "[interrupted]\n\nexit: -1"
   }
@@ -1018,6 +1038,7 @@ func AL(ctx context.Context, cfg *Cfg, msgs []Message, sp string, depth int) ([]
     if u.Cached() > 0 { turnUsage.CachedTokens = u.Cached() }
     for j := range m.ToolCalls {
       tc := &m.ToolCalls[j]
+      tc.Function.Arguments = filterText(tc.Function.Arguments)
       astr := tc.Function.Arguments
       var a map[string]any
       if err := json.Unmarshal([]byte(astr), &a); err != nil || a == nil {
@@ -1035,7 +1056,7 @@ func AL(ctx context.Context, cfg *Cfg, msgs []Message, sp string, depth int) ([]
     if len(m.ToolCalls) == 0 { done = true; break }
     for _, tc := range m.ToolCalls {
       if err := ctx.Err(); err != nil { return msgs, turnUsage, err }
-      fn, astr := tc.Function.Name, tc.Function.Arguments
+      fn, astr := tc.Function.Name, filterText(tc.Function.Arguments)
       fmt.Println(c(fmt.Sprintf("[tool call: %s(%s)]", fn, astr), 33))
       res, sty := "", 2
       var a map[string]any
@@ -1045,10 +1066,12 @@ func AL(ctx context.Context, cfg *Cfg, msgs []Message, sp string, depth int) ([]
         switch fn {
         case "shell_exec":
           cmd, _ := a["command"].(string)
+          cmd = filterText(cmd)
           res = shell(ctx, cmd, cfg.ShellTimeout)
           if err := ctx.Err(); err != nil { return msgs, turnUsage, err }
         case "run_subagent":
           pr, _ := a["prompt"].(string)
+          pr = filterText(pr)
           if depth >= MAX_DEPTH {
             res, sty = fmt.Sprintf("[subagent depth limit (%d) reached, child not spawned]", MAX_DEPTH), 31
           } else {
@@ -1064,13 +1087,14 @@ func AL(ctx context.Context, cfg *Cfg, msgs []Message, sp string, depth int) ([]
             } else {
               turnUsage.CompletionTokens += subu.CompletionTokens
               turnUsage.TotalTokens += subu.TotalTokens
-              res, sty = last(subr), 2
+              res, sty = filterText(last(subr)), 2
             }
           }
         default:
           res, sty = "Unknown tool: " + fn, 31
         }
       }
+      res = filterText(res)
       fmt.Println(c("[tool result: "+fn+"]", 32) + "\n" + c(res, sty) + "\n")
       msgs = append(msgs, Message{Role: "tool", ToolCallID: tc.ID, Content: strp(res)})
     }
@@ -1422,7 +1446,7 @@ func main() {
     }
     u := strings.TrimSpace(string(data))
     if strings.HasPrefix(u, "!") {
-      cmd := strings.TrimSpace(strings.TrimPrefix(u, "!"))
+      cmd := filterText(strings.TrimSpace(strings.TrimPrefix(u, "!")))
       if cmd != "" {
         astr, _ := json.Marshal(map[string]string{"command": cmd})
         fmt.Println(c(fmt.Sprintf("[tool call: shell_exec(%s)]", string(astr)), 33))
@@ -1551,7 +1575,7 @@ func main() {
       }
       continue
     case strings.HasPrefix(u, "!"):
-      cmd := strings.TrimSpace(strings.TrimPrefix(u, "!"))
+      cmd := filterText(strings.TrimSpace(strings.TrimPrefix(u, "!")))
       if cmd != "" {
         astr, _ := json.Marshal(map[string]string{"command": cmd})
         fmt.Println(c(fmt.Sprintf("[tool call: shell_exec(%s)]", string(astr)), 33))
diff --git a/main_test.go b/main_test.go
index c309e32..5c6fd16 100644
--- a/main_test.go
+++ b/main_test.go
@@ -1851,6 +1851,95 @@ func TestFetchContextWindowFallbackConfig(t *testing.T) {
   }
 }
 
+func TestFilterText(t *testing.T) {
+  cases := []struct {
+    name     string
+    input    string
+    expected string
+  }{
+    {
+      name:     "ASCII printable, spaces, tabs, newlines",
+      input:    "Hello World!\t123\nLine 2 ~`@#$%",
+      expected: "Hello World!\t123\nLine 2 ~`@#$%",
+    },
+    {
+      name:     "CRLF normalization",
+      input:    "line1\r\nline2\r\n",
+      expected: "line1\nline2\n",
+    },
+    {
+      name:     "Unicode printable letters, numbers, punctuation",
+      input:    "こんにちは世界！ Привет мир! 123 αβγ €$¥",
+      expected: "こんにちは世界！ Привет мир! 123 αβγ €$¥",
+    },
+    {
+      name:     "Control characters stripped",
+      input:    "null\x00bell\x07esc\x1b[31mred\x1b[0m\x7fdel",
+      expected: "nullbellesc[31mred[0mdel",
+    },
+    {
+      name:     "Zero-width and format characters stripped",
+      input:    "hidden\u200Binjection\u200Cand\u200Djoiner\uFEFFbom\u202Ebidi\U000E0001tag",
+      expected: "hiddeninjectionandjoinerbombiditag",
+    },
+    {
+      name:     "Space-like unicode characters stripped",
+      input:    "nbsp\u00A0space\u2000enquad\u2001emquad\u2009thin\u202Fnarrow\u3000ideo\u1680ogham\u2028lsep\u2029psep",
+      expected: "nbspspaceenquademquadthinnarrowideooghamlseppsep",
+    },
+  }
+
+  for _, tc := range cases {
+    t.Run(tc.name, func(t *testing.T) {
+      got := filterText(tc.input)
+      if got != tc.expected {
+        t.Errorf("filterText(%q) = %q, expected %q", tc.input, got, tc.expected)
+      }
+    })
+  }
+}
+
+func TestSanitizeMessagesWithInvisibles(t *testing.T) {
+  msgs := []Message{
+    {
+      Role: "assistant",
+      ToolCalls: []ToolCall{
+        {
+          ID:   "call_1",
+          Type: "function",
+          Function: struct {
+            Name      string `json:"name"`
+            Arguments string `json:"arguments"`
+          }{
+            Name:      "shell_exec",
+            Arguments: "{\"command\": \"cat\u200B \u00A0file.txt\"}",
+          },
+        },
+      },
+    },
+    {
+      Role:       "tool",
+      ToolCallID: "call_1",
+      Content:    strp("output\u200B\x00with\u00A0invisible\r\nexit: 0"),
+    },
+  }
+
+  sanitizeMessages(msgs)
+
+  tcArgs := msgs[0].ToolCalls[0].Function.Arguments
+  if strings.Contains(tcArgs, "\u200B") || strings.Contains(tcArgs, "\u00A0") {
+    t.Errorf("Tool call arguments still contain invisible characters: %q", tcArgs)
+  }
+
+  toolContent := *msgs[1].Content
+  if strings.Contains(toolContent, "\u200B") || strings.Contains(toolContent, "\x00") || strings.Contains(toolContent, "\u00A0") || strings.Contains(toolContent, "\r") {
+    t.Errorf("Tool content still contains invisible characters: %q", toolContent)
+  }
+  if !strings.Contains(toolContent, "outputwithinvisible\nexit: 0") {
+    t.Errorf("Tool content unexpected: %q", toolContent)
+  }
+}
+
 
 
 
diff --git a/mb b/mb
index ed7d410..9777707 100755
--- a/mb
+++ b/mb
@@ -21,9 +21,18 @@ sub sp { my $p = '';
   $p =~ s/^\s+|\s+$//g;
   length($p) ? $p : $DEF_SP; }
 
+sub filter_text { my $s = shift // ''; $s =~ s/[^\x20\t\n\p{L}\p{N}\p{P}\p{S}\p{M}]//g; $s }
+
 sub T { my ($n, $d, $p) = @_; {type=>'function', function=>{name=>$n, description=>$d, parameters=>{type=>'object', properties=>$p, required=>[keys %$p]}}} }
 
-sub sanitize_msgs { for my $m (@{$_[0]}) { if (ref $m eq 'HASH' && $m->{tool_calls}) { for my $tc (@{$m->{tool_calls}}) { my $a = eval { decode_json($tc->{function}{arguments} // '{}') }; $tc->{function}{arguments} = encode_json({invalid_raw => $tc->{function}{arguments} // ''}) if ref $a ne 'HASH'; } } } }
+sub sanitize_msgs { for my $m (@{$_[0]}) { if (ref $m eq 'HASH') {
+  if ($m->{tool_calls}) { for my $tc (@{$m->{tool_calls}}) {
+    $tc->{function}{arguments} = filter_text($tc->{function}{arguments});
+    my $a = eval { decode_json($tc->{function}{arguments} // '{}') };
+    $tc->{function}{arguments} = encode_json({invalid_raw => $tc->{function}{arguments} // ''}) if ref $a ne 'HASH';
+  } }
+  elsif ($m->{role} && $m->{role} eq 'tool' && defined $m->{content}) { $m->{content} = filter_text($m->{content}); }
+} } }
 
 sub llm { my ($c, $msgs) = @_; # one non-streaming chat completion
   sanitize_msgs($msgs);
@@ -43,10 +52,12 @@ sub llm { my ($c, $msgs) = @_; # one non-streaming chat completion
   die "API error: " . (length($rb) ? "$rb (HTTP $r->{status})" : ($r->{reason} || "HTTP $r->{status}")) . "\n"; }
 
 sub shell_exec { my ($cmd, $t) = @_; # run a command under a hard timeout
+  $cmd = filter_text($cmd);
   my $out = '';
   eval { local $SIG{ALRM} = sub { alarm 0; die "timeout\n" }; alarm $t; $out = `$cmd 2>&1`; alarm 0; };
   $out =~ s/\s+$//;
   utf8::decode($out);
+  $out = filter_text($out);
   $@ ? "$out\n[timeout after ${t}s]\nexit: -1" : "$out\nexit: " . ($? >> 8); }
 
 sub last_assistant { for my $m (reverse @{$_[0]}) { return $m->{content} if $m->{role} eq 'assistant' && defined $m->{content} && length $m->{content}; } '' }
@@ -66,12 +77,14 @@ sub AL { my ($c, $msgs, $sp, $depth) = @_; # the agentic loop: LLM <-> tools unt
     last unless $tcs && @$tcs;
     for my $tc (@$tcs) {
       my $fn = $tc->{function}{name};
+      $tc->{function}{arguments} = filter_text($tc->{function}{arguments});
       my $a = eval { decode_json($tc->{function}{arguments} // '{}') };
       my $res;
       if (ref $a ne 'HASH') { $tc->{function}{arguments} = encode_json({invalid_raw => $tc->{function}{arguments} // ''}); $res = "bad JSON args for $fn: " . ($tc->{function}{arguments} // ''); }
-      elsif ($fn eq 'shell_exec') { $res = shell_exec($a->{command} // '', $c->{shell_timeout}); }
-      elsif ($fn eq 'run_subagent') { $res = $depth >= 5 ? '[subagent depth limit (5) reached, child not spawned]' : last_assistant(AL($c, [{role=>'system', content=>"$sp\n\nImportant: this is a child agent"}, {role=>'user', content=>$a->{prompt} // ''}], $sp, $depth + 1)); }
+      elsif ($fn eq 'shell_exec') { $res = shell_exec(filter_text($a->{command} // ''), $c->{shell_timeout}); }
+      elsif ($fn eq 'run_subagent') { $res = $depth >= 5 ? '[subagent depth limit (5) reached, child not spawned]' : filter_text(last_assistant(AL($c, [{role=>'system', content=>"$sp\n\nImportant: this is a child agent"}, {role=>'user', content=>filter_text($a->{prompt} // '')}], $sp, $depth + 1))); }
       else { $res = "unknown tool: $fn"; }
+      $res = filter_text($res);
       print "[tool] $fn: $res\n";
       push @$msgs, {role=>'tool', tool_call_id=>$tc->{id}, content=>$res};
     }