diff --git a/skyvern/forge/sdk/workflow/models/block.py b/skyvern/forge/sdk/workflow/models/block.py
index 6c220193..7676b0f9 100644
--- a/skyvern/forge/sdk/workflow/models/block.py
+++ b/skyvern/forge/sdk/workflow/models/block.py
@@ -3969,7 +3969,7 @@ class JinjaBranchCriteria(BranchCriteria):
 class BranchCondition(BaseModel):
     """Represents a single conditional branch edge within a ConditionalBlock."""
 
-    criteria: BranchCriteria | None = None
+    criteria: BranchCriteriaTypeVar | None = None
     next_block_label: str | None = None
     description: str | None = None
     is_default: bool = False
@@ -4085,3 +4085,7 @@ BlockSubclasses = Union[
     HttpRequestBlock,
 ]
 BlockTypeVar = Annotated[BlockSubclasses, Field(discriminator="block_type")]
+
+
+BranchCriteriaSubclasses = Union[JinjaBranchCriteria]
+BranchCriteriaTypeVar = Annotated[BranchCriteriaSubclasses, Field(discriminator="criteria_type")]
diff --git a/skyvern/schemas/workflows.py b/skyvern/schemas/workflows.py
index d1579cce..a7f57569 100644
--- a/skyvern/schemas/workflows.py
+++ b/skyvern/schemas/workflows.py
@@ -3,7 +3,7 @@ from dataclasses import dataclass
 from enum import StrEnum
 from typing import Annotated, Any, Literal
 
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, Field, field_validator, model_validator
 
 from skyvern.config import settings
 from skyvern.forge.sdk.workflow.models.parameter import OutputParameter, ParameterType, WorkflowParameterType
@@ -258,6 +258,44 @@ class ForLoopBlockYAML(BlockYAML):
     complete_if_empty: bool = False
 
 
+class BranchCriteriaYAML(BaseModel):
+    criteria_type: Literal["jinja2_template"] = "jinja2_template"
+    expression: str
+    description: str | None = None
+
+
+class BranchConditionYAML(BaseModel):
+    criteria: BranchCriteriaYAML | None = None
+    next_block_label: str | None = None
+    description: str | None = None
+    is_default: bool = False
+
+    @model_validator(mode="after")
+    def validate_condition(cls, condition: "BranchConditionYAML") -> "BranchConditionYAML":
+        if condition.criteria is None and not condition.is_default:
+            raise ValueError("Branches without criteria must be marked as default.")
+        if condition.criteria is not None and condition.is_default:
+            raise ValueError("Default branches may not define criteria.")
+        return condition
+
+
+class ConditionalBlockYAML(BlockYAML):
+    block_type: Literal[BlockType.CONDITIONAL] = BlockType.CONDITIONAL  # type: ignore
+
+    branch_conditions: list[BranchConditionYAML] = Field(default_factory=list)
+
+    @model_validator(mode="after")
+    def validate_branches(cls, block: "ConditionalBlockYAML") -> "ConditionalBlockYAML":
+        if not block.branch_conditions:
+            raise ValueError("Conditional blocks require at least one branch.")
+
+        default_branches = [branch for branch in block.branch_conditions if branch.is_default]
+        if len(default_branches) > 1:
+            raise ValueError("Only one default branch is permitted per conditional block.")
+
+        return block
+
+
 class CodeBlockYAML(BlockYAML):
     # There is a mypy bug with Literal. Without the type: ignore, mypy will raise an error:
     # Parameter 1 of Literal[...] cannot be of type "Any"
@@ -538,6 +576,7 @@ BLOCK_YAML_SUBCLASSES = (
     | PDFParserBlockYAML
     | TaskV2BlockYAML
     | HttpRequestBlockYAML
+    | ConditionalBlockYAML
 )
 BLOCK_YAML_TYPES = Annotated[BLOCK_YAML_SUBCLASSES, Field(discriminator="block_type")]
 
@@ -547,6 +586,20 @@ class WorkflowDefinitionYAML(BaseModel):
     parameters: list[PARAMETER_YAML_TYPES]
     blocks: list[BLOCK_YAML_TYPES]
 
+    @model_validator(mode="after")
+    def validate_unique_block_labels(cls, workflow: "WorkflowDefinitionYAML") -> "WorkflowDefinitionYAML":
+        labels = [block.label for block in workflow.blocks]
+        duplicates = [label for label in labels if labels.count(label) > 1]
+
+        if duplicates:
+            unique_duplicates = sorted(set(duplicates))
+            raise ValueError(
+                f"Block labels must be unique within a workflow. "
+                f"Found duplicate label(s): {', '.join(unique_duplicates)}"
+            )
+
+        return workflow
+
 
 class WorkflowCreateYAMLRequest(BaseModel):
     title: str