diff --git a/commands/handler.go b/commands/handler.go
index 3b92a908..56f27f06 100644
--- a/commands/handler.go
+++ b/commands/handler.go
@@ -33,6 +33,7 @@ type Handler[MetaType any] struct {
 	// Parameters is a description of structured command parameters.
 	// If set, the StructuredArgs field of Event will be populated.
 	Parameters []*cmdschema.Parameter
+	TailParam  string
 
 	parents             []*Handler[MetaType]
 	nestedNameCache     []string
@@ -68,9 +69,18 @@ func (h *Handler[MetaType]) Spec() *cmdschema.EventContent {
 		Aliases:     names[1:],
 		Parameters:  h.Parameters,
 		Description: h.Description,
+		TailParam:   h.TailParam,
 	}
 }
 
+func (h *Handler[MetaType]) CopyFrom(other *Handler[MetaType]) {
+	if h.Parameters == nil {
+		h.Parameters = other.Parameters
+		h.TailParam = other.TailParam
+	}
+	h.Func = other.Func
+}
+
 func (h *Handler[MetaType]) initSubcommandContainer() {
 	if len(h.Subcommands) > 0 {
 		h.subcommandContainer = NewCommandContainer[MetaType]()
diff --git a/commands/processor.go b/commands/processor.go
index 0089226f..80f6745d 100644
--- a/commands/processor.go
+++ b/commands/processor.go
@@ -108,6 +108,7 @@ func (proc *Processor[MetaType]) Process(ctx context.Context, evt *event.Event)
 		}
 	}
 	if parsed.StructuredArgs != nil && len(parsed.Args) > 0 {
+		// TODO allow unknown command handlers to be called?
 		// The client sent MSC4391 data, but the target command wasn't found
 		log.Debug().Msg("Didn't find handler for MSC4391 command")
 		return
diff --git a/event/cmdschema/content.go b/event/cmdschema/content.go
index b69f0c1f..e7f362ed 100644
--- a/event/cmdschema/content.go
+++ b/event/cmdschema/content.go
@@ -13,6 +13,7 @@ import (
 	"reflect"
 	"slices"
 
+	"go.mau.fi/util/exsync"
 	"go.mau.fi/util/ptr"
 
 	"maunium.net/go/mautrix/event"
@@ -24,6 +25,7 @@ type EventContent struct {
 	Aliases     []string                       `json:"aliases,omitempty"`
 	Parameters  []*Parameter                   `json:"parameters,omitempty"`
 	Description *event.ExtensibleTextContainer `json:"description,omitempty"`
+	TailParam   string                         `json:"fi.mau.tail_parameter,omitempty"`
 }
 
 func (ec *EventContent) Validate() error {
@@ -32,11 +34,22 @@ func (ec *EventContent) Validate() error {
 	} else if ec.Command == "" {
 		return fmt.Errorf("command is empty")
 	}
+	var tailFound bool
+	dupMap := exsync.NewSet[string]()
 	for i, p := range ec.Parameters {
 		if err := p.Validate(); err != nil {
 			return fmt.Errorf("parameter %q (#%d) is invalid: %w", ptr.Val(p).Key, i+1, err)
+		} else if !dupMap.Add(p.Key) {
+			return fmt.Errorf("duplicate parameter key %q at #%d", p.Key, i+1)
+		} else if p.Key == ec.TailParam {
+			tailFound = true
+		} else if tailFound && !p.Optional {
+			return fmt.Errorf("required parameter %q (#%d) is after tail parameter %q", p.Key, i+1, ec.TailParam)
 		}
 	}
+	if ec.TailParam != "" && !tailFound {
+		return fmt.Errorf("tail parameter %q not found in parameters", ec.TailParam)
+	}
 	return nil
 }
 
diff --git a/event/cmdschema/parse.go b/event/cmdschema/parse.go
index 5269ab28..91a02827 100644
--- a/event/cmdschema/parse.go
+++ b/event/cmdschema/parse.go
@@ -135,8 +135,8 @@ func (ec *EventContent) ParseArguments(input string) (json.RawMessage, error) {
 			args[param.Key] = collector
 		} else {
 			nextVal, input, wasQuoted = parseQuoted(input)
-			if isLast && !wasQuoted && len(input) > 0 {
-				// If the last argument is not quoted and not variadic, just treat the rest of the string
+			if isLast && !wasQuoted && len(input) > 0 && !strings.Contains(input, "--") {
+				// If the last argument is not quoted and doesn't have flags, just treat the rest of the string
 				// as the argument without escapes (arguments with escapes should be quoted).
 				nextVal += " " + input
 				input = ""
@@ -146,7 +146,7 @@ func (ec *EventContent) ParseArguments(input string) (json.RawMessage, error) {
 				args[param.Key] = true
 				return
 			}
-			if nextVal == "" && !param.Optional {
+			if nextVal == "" && !wasQuoted && !isNamed && !param.Optional {
 				setError(fmt.Errorf("missing value for required parameter %s", param.Key))
 			}
 			parsedVal, err := param.Schema.ParseString(nextVal)
@@ -180,10 +180,11 @@ func (ec *EventContent) ParseArguments(input string) (json.RawMessage, error) {
 				break
 			}
 		}
-		if skipParams[i] {
+		isTail := param.Key == ec.TailParam
+		if skipParams[i] || (param.Optional && !isTail) {
 			continue
 		}
-		processParameter(param, i == len(ec.Parameters)-1, false)
+		processParameter(param, i == len(ec.Parameters)-1 || isTail, false)
 	}
 	jsonArgs, marshalErr := json.Marshal(args)
 	if marshalErr != nil {
diff --git a/event/cmdschema/parse_test.go b/event/cmdschema/parse_test.go
index 725b0150..1e0d1817 100644
--- a/event/cmdschema/parse_test.go
+++ b/event/cmdschema/parse_test.go
@@ -109,7 +109,7 @@ func TestMSC4391BotCommandEventContent_ParseInput(t *testing.T) {
 						assert.Nil(t, output)
 					} else {
 						assert.Equal(t, ctd.Spec.Command, output.MSC4391BotCommand.Command)
-						assert.Equal(t, outputStr, exbytes.UnsafeString(output.MSC4391BotCommand.Arguments))
+						assert.Equalf(t, outputStr, exbytes.UnsafeString(output.MSC4391BotCommand.Arguments), "Input: %s", test.Input)
 					}
 				})
 			}
diff --git a/event/cmdschema/testdata/commands/flags.json b/event/cmdschema/testdata/commands/flags.json
index dedde348..469986f0 100644
--- a/event/cmdschema/testdata/commands/flags.json
+++ b/event/cmdschema/testdata/commands/flags.json
@@ -27,7 +27,8 @@
 				"optional": true,
 				"fi.mau.default_value": false
 			}
-		]
+		],
+		"fi.mau.tail_parameter": "user"
 	},
 	"tests": [
 		{
@@ -35,17 +36,15 @@
 			"input": "/flag mrrp",
 			"output": {
 				"meow": "mrrp",
-				"user": null,
-				"woof": false
+				"user": null
 			}
 		},
 		{
-			"name": "positional flag",
-			"input": "/flag mrrp @user:example.com yes",
+			"name": "no flags, has tail",
+			"input": "/flag mrrp @user:example.com",
 			"output": {
 				"meow": "mrrp",
-				"user": "@user:example.com",
-				"woof": true
+				"user": "@user:example.com"
 			}
 		},
 		{
@@ -130,18 +129,9 @@
 				"woof": true
 			}
 		},
-		{
-			"name": "only string variables named",
-			"input": "/flag --user=@user:example.com --meow=mrrp yes",
-			"output": {
-				"meow": "mrrp",
-				"user": "@user:example.com",
-				"woof": true
-			}
-		},
 		{
 			"name": "invalid value for named parameter",
-			"input": "/flag --user=meowings mrrp yes",
+			"input": "/flag --user=meowings mrrp --woof",
 			"error": true,
 			"output": {
 				"meow": "mrrp",