diff --git a/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/HumanDecisionBlockConfiguration.java b/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/HumanDecisionBlockConfiguration.java
index 14034bb..bf77b8f 100644
--- a/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/HumanDecisionBlockConfiguration.java
+++ b/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/HumanDecisionBlockConfiguration.java
@@ -5,6 +5,7 @@ import java.util.List;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 
+import it.cnr.isti.workflow.manager.blocks.factories.TemplateInputs;
 import it.cnr.isti.workflow.manager.blocks.types.HumanDecisionBlockType;
 import it.cnr.isti.workflow.manager.configurations.annotations.LongText;
 import it.cnr.isti.workflow.manager.configurations.annotations.Structural;
@@ -75,6 +76,12 @@ public class HumanDecisionBlockConfiguration extends BlockConfiguration<HumanDec
                 .build();
     }
 
+    @AssertTrue(message = "question placeholder names must start with a letter and contain only letters, digits, '-' or '_'")
+    @JsonIgnore
+    boolean isQuestionPlaceholderNamesValid() {
+        return TemplateInputs.hasValidPlaceholderNames(question);
+    }
+
     @AssertTrue(message = "options must contain unique non-blank names")
     @JsonIgnore
     boolean isOptionsUnique() {
diff --git a/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/HumanInteractiveBlockConfiguration.java b/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/HumanInteractiveBlockConfiguration.java
index 2eab81b..27458af 100644
--- a/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/HumanInteractiveBlockConfiguration.java
+++ b/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/HumanInteractiveBlockConfiguration.java
@@ -1,9 +1,12 @@
 package it.cnr.isti.workflow.manager.blocks.configurations;
 
+import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 
+import it.cnr.isti.workflow.manager.blocks.factories.TemplateInputs;
 import it.cnr.isti.workflow.manager.configurations.annotations.LongText;
 import it.cnr.isti.workflow.manager.blocks.types.HumanInteractionBlockType;
+import jakarta.validation.constraints.AssertTrue;
 import jakarta.validation.constraints.NotBlank;
 import lombok.Builder;
 import lombok.Data;
@@ -40,5 +43,10 @@ public class HumanInteractiveBlockConfiguration extends BlockConfiguration<Human
         return configuration;
     }
 
+    @AssertTrue(message = "actionDescription placeholder names must start with a letter and contain only letters, digits, '-' or '_'")
+    @JsonIgnore
+    boolean isActionDescriptionPlaceholderNamesValid() {
+        return TemplateInputs.hasValidPlaceholderNames(actionDescription);
+    }
 
 }
diff --git a/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/LLMBlockConfiguration.java b/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/LLMBlockConfiguration.java
index d3c848c..56f49ec 100644
--- a/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/LLMBlockConfiguration.java
+++ b/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/LLMBlockConfiguration.java
@@ -2,8 +2,10 @@ package it.cnr.isti.workflow.manager.blocks.configurations;
 
 import java.util.List;
 
+import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 
+import it.cnr.isti.workflow.manager.blocks.factories.TemplateInputs;
 import it.cnr.isti.workflow.manager.blocks.types.LLMBlockType;
 import it.cnr.isti.workflow.manager.configurations.annotations.LongText;
 import it.cnr.isti.workflow.manager.configurations.annotations.Structural;
@@ -68,6 +70,12 @@ public class LLMBlockConfiguration extends BlockConfiguration<LLMBlockType> {
         return configuration;
     }
 
+    @AssertTrue(message = "prompt placeholder names must start with a letter and contain only letters, digits, '-' or '_'")
+    @JsonIgnore
+    boolean isPromptPlaceholderNamesValid() {
+        return TemplateInputs.hasValidPlaceholderNames(prompt);
+    }
+
     @AssertTrue(message = "skills must have unique skillId values")
     boolean areSkillIdsUnique() {
         if (skills == null || skills.isEmpty()) {
diff --git a/src/main/java/it/cnr/isti/workflow/manager/blocks/factories/TemplateInputs.java b/src/main/java/it/cnr/isti/workflow/manager/blocks/factories/TemplateInputs.java
index 68957c8..fcf0353 100644
--- a/src/main/java/it/cnr/isti/workflow/manager/blocks/factories/TemplateInputs.java
+++ b/src/main/java/it/cnr/isti/workflow/manager/blocks/factories/TemplateInputs.java
@@ -16,10 +16,19 @@ import it.cnr.isti.workflow.manager.ios.IOType;
  * description, a decision question, ...), so a block can expose more than
  * one upstream-wired input without a separate explicit input list.
  */
-final class TemplateInputs {
+public final class TemplateInputs {
 
     private static final Pattern PLACEHOLDER = Pattern.compile("\\$\\{\\{(.*?)}}");
 
+    // Allows '.' since it is already a load-bearing separator for LoopContainer
+    // guard template values (inputs.<name> / outputs.<name>, see
+    // ExecutionsService.buildGuardTemplateValues) and for container-qualified
+    // exposed names (nodeName.ioName, see
+    // ContainerFlowInterfaceResolver.qualifyWithNodeName). Deliberately excludes
+    // '[' and ']' so a future marker syntax on placeholder names (e.g. an
+    // array-input suffix) can be introduced unambiguously later.
+    private static final Pattern VALID_NAME = Pattern.compile("^[A-Za-z][A-Za-z0-9_.-]*$");
+
     private TemplateInputs() {
     }
 
@@ -41,4 +50,13 @@ final class TemplateInputs {
     static List<IODescriptor> toInputs(Set<String> names, IOType type, List<IOCapability> capabilities) {
         return names.stream().map(name -> IODescriptor.input(name, type, false, capabilities)).toList();
     }
+
+    /**
+     * Whether every {@code ${{name}}} placeholder found in the given text has
+     * a name that starts with a letter and contains only letters, digits,
+     * '-' or '_'.
+     */
+    public static boolean hasValidPlaceholderNames(String text) {
+        return extractNames(text).stream().allMatch(name -> VALID_NAME.matcher(name).matches());
+    }
 }
diff --git a/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/BlockConfigurationValidationTest.java b/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/BlockConfigurationValidationTest.java
index 9b73130..64cdd84 100644
--- a/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/BlockConfigurationValidationTest.java
+++ b/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/BlockConfigurationValidationTest.java
@@ -121,6 +121,75 @@ class BlockConfigurationValidationTest {
         assertTrue(validator.validate(configuration).isEmpty());
     }
 
+    @Test
+    void humanDecisionRejectsMalformedPlaceholderNameInQuestion() {
+        HumanDecisionBlockConfiguration configuration = HumanDecisionBlockConfiguration.builder()
+                .name("decision")
+                .question("Proceed for ${{candidate profile}}?")
+                .options(List.of(new HumanDecisionOption("yes", "Yes"), new HumanDecisionOption("no", "No")))
+                .build();
+
+        Set<ConstraintViolation<HumanDecisionBlockConfiguration>> violations = validator.validate(configuration);
+        assertTrue(violations.stream().anyMatch(v -> v.getMessage().contains("placeholder names")));
+    }
+
+    @Test
+    void humanDecisionAcceptsDottedPlaceholderNameInQuestion() {
+        HumanDecisionBlockConfiguration configuration = HumanDecisionBlockConfiguration.builder()
+                .name("decision")
+                .question("Proceed given ${{outputs.response}}?")
+                .options(List.of(new HumanDecisionOption("yes", "Yes"), new HumanDecisionOption("no", "No")))
+                .build();
+
+        assertTrue(validator.validate(configuration).isEmpty());
+    }
+
+    @Test
+    void llmBlockRejectsMalformedPlaceholderNameInPrompt() {
+        LLMBlockConfiguration configuration = LLMBlockConfiguration.builder()
+                .name("llm")
+                .llmDescriptor(it.cnr.isti.workflow.manager.llms.LLMDescriptor.builder()
+                        .provider("testProvider").model("testModel").build())
+                .prompt("Summarize ${{candidate!}}")
+                .build();
+
+        Set<ConstraintViolation<LLMBlockConfiguration>> violations = validator.validate(configuration);
+        assertTrue(violations.stream().anyMatch(v -> v.getMessage().contains("placeholder names")));
+    }
+
+    @Test
+    void llmBlockAcceptsAWellFormedPrompt() {
+        LLMBlockConfiguration configuration = LLMBlockConfiguration.builder()
+                .name("llm")
+                .llmDescriptor(it.cnr.isti.workflow.manager.llms.LLMDescriptor.builder()
+                        .provider("testProvider").model("testModel").build())
+                .prompt("Summarize ${{candidate-profile}}")
+                .build();
+
+        assertTrue(validator.validate(configuration).isEmpty());
+    }
+
+    @Test
+    void humanInteractionRejectsMalformedPlaceholderNameInActionDescription() {
+        HumanInteractiveBlockConfiguration configuration = HumanInteractiveBlockConfiguration.builder()
+                .name("interaction")
+                .actionDescription("Review ${{candidate[]}} and decide")
+                .build();
+
+        Set<ConstraintViolation<HumanInteractiveBlockConfiguration>> violations = validator.validate(configuration);
+        assertTrue(violations.stream().anyMatch(v -> v.getMessage().contains("placeholder names")));
+    }
+
+    @Test
+    void humanInteractionAcceptsAWellFormedActionDescription() {
+        HumanInteractiveBlockConfiguration configuration = HumanInteractiveBlockConfiguration.builder()
+                .name("interaction")
+                .actionDescription("Review ${{candidate_profile}} and decide")
+                .build();
+
+        assertTrue(validator.validate(configuration).isEmpty());
+    }
+
     @Test
     void endBlockRequiresAnOutcomeCode() {
         EndBlockConfiguration configuration = EndBlockConfiguration.builder()