diff --git a/router/src/validation.rs b/router/src/validation.rs
index f350d15e820..204dbf92a6a 100644
--- a/router/src/validation.rs
+++ b/router/src/validation.rs
@@ -1,7 +1,9 @@
 /// Payload validation logic
 use crate::validation::ValidationError::{BestOfSampling, BestOfSeed, EmptyInput};
 use crate::{GenerateParameters, GenerateRequest, GrammarType};
+use jsonschema::{Draft, JSONSchema};
 use rand::{thread_rng, Rng};
+use serde_json::Value;
 use text_generation_client::{
     GrammarType as ProtoGrammarType, NextTokenChooserParameters, StoppingCriteriaParameters,
 };
@@ -313,14 +315,24 @@ impl Validation {
                     return Err(ValidationError::Grammar);
                 }
                 match grammar {
-                    // currently both are handled the same way since compilation is done in Python
                     GrammarType::Json(json) => {
-                        // JSONSchema::options()
-                        //     .with_draft(Draft::Draft202012)
-                        //     .compile(&json)
-                        //     .map_err(|e| ValidationError::InvalidGrammar(e.to_string()))?;
+                        let json = match json {
+                            // if value is a string, we need to parse it again to make sure its
+                            // a valid json
+                            Value::String(s) => serde_json::from_str(&s)
+                                .map_err(|e| ValidationError::InvalidGrammar(e.to_string())),
+                            Value::Object(_) => Ok(json),
+                            _ => Err(ValidationError::Grammar),
+                        }?;
+
+                        // Check if the json is a valid JSONSchema
+                        JSONSchema::options()
+                            .with_draft(Draft::Draft202012)
+                            .compile(&json)
+                            .map_err(|e| ValidationError::InvalidGrammar(e.to_string()))?;
 
                         (
+                            // Serialize json to string
                             serde_json::to_string(&json)
                                 .map_err(|e| ValidationError::InvalidGrammar(e.to_string()))?,
                             ProtoGrammarType::Json.into(),
@@ -497,7 +509,7 @@ pub enum ValidationError {
     Tokenizer(String),
     #[error("grammar is not supported")]
     Grammar,
-    #[error("grammar is not a valid JSONSchema: {0}")]
+    #[error("grammar is not valid: {0}")]
     InvalidGrammar(String),
 }