diff --git a/Cargo.lock b/Cargo.lock
index b7b402f..1c3b175 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1105,6 +1105,7 @@ name = "duperfmt"
 version = "0.1.1"
 dependencies = [
  "clap",
+ "insta",
  "miette",
  "thiserror 2.0.17",
  "topiary-core",
@@ -1723,9 +1724,9 @@ dependencies = [
 
 [[package]]
 name = "insta"
-version = "1.43.2"
+version = "1.44.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "46fdb647ebde000f43b5b53f773c30cf9b0cb4300453208713fa38b2c70935a0"
+checksum = "b5c943d4415edd8153251b6f197de5eb1640e56d84e8d9159bea190421c73698"
 dependencies = [
  "console",
  "once_cell",
diff --git a/axum_duper/CHANGELOG.md b/axum_duper/CHANGELOG.md
index 57698a4..1487eeb 100644
--- a/axum_duper/CHANGELOG.md
+++ b/axum_duper/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Changed
 
 - Bump `duper` to 0.6.0.
+- Handle `Content-Type: application/json` requests in extractor.
 
 ## 0.4.2 (2025-12-07)
 
diff --git a/axum_duper/src/lib.rs b/axum_duper/src/lib.rs
index 2faafff..f54f5d6 100644
--- a/axum_duper/src/lib.rs
+++ b/axum_duper/src/lib.rs
@@ -18,8 +18,11 @@ use serde_core::{Serialize, de::DeserializeOwned};
 
 /// Default MIME type for Duper files.
 pub static DUPER_CONTENT_TYPE: &str = "application/duper";
-/// Alternative MIME type for Duper files.
+/// Alternative MIME type for Duper files, handled by the Duper extractor.
 pub static DUPER_ALT_CONTENT_TYPE: &str = "application/x-duper";
+/// Default MIME type for JSON files, handled by the Duper extractor (given
+/// that Duper is a superset of JSON).
+pub static JSON_CONTENT_TYPE: &str = "application/json";
 
 /// Rejection used for [`Duper`].
 ///
@@ -168,15 +171,23 @@ where
             .headers()
             .get(CONTENT_TYPE)
             .and_then(|content_type| content_type.to_str().ok())
-            && (content_type == DUPER_CONTENT_TYPE || content_type == DUPER_ALT_CONTENT_TYPE)
         {
-            let string = String::from_request(req, state)
-                .await
-                .map_err(|_| DuperRejection::DuperDataError)?;
-            Self::from_string(&string)
-        } else {
-            Err(DuperRejection::MissingDuperContentType)
+            let content_type = if let Some((content_type, _)) = content_type.split_once(';') {
+                content_type
+            } else {
+                content_type
+            };
+            if content_type == DUPER_CONTENT_TYPE
+                || content_type == DUPER_ALT_CONTENT_TYPE
+                || content_type == JSON_CONTENT_TYPE
+            {
+                let string = String::from_request(req, state)
+                    .await
+                    .map_err(|_| DuperRejection::DuperDataError)?;
+                return Self::from_string(&string);
+            }
         }
+        Err(DuperRejection::MissingDuperContentType)
     }
 }
 
diff --git a/duper-python/CHANGELOG.md b/duper-python/CHANGELOG.md
index 6095b87..6bfd224 100644
--- a/duper-python/CHANGELOG.md
+++ b/duper-python/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### Changed
 
 - Bump `duper` to 0.6.0.
+- Handle `Content-Type: application/json` requests in FastAPI dependency.
 
 ## 0.4.2 (2025-12-07)
 
diff --git a/duper-python/python/duper/fastapi.py b/duper-python/python/duper/fastapi.py
index f1f7506..ad22aac 100644
--- a/duper-python/python/duper/fastapi.py
+++ b/duper-python/python/duper/fastapi.py
@@ -16,6 +16,7 @@ __all__ = [
 
 DUPER_CONTENT_TYPE = "application/duper"
 DUPER_ALT_CONTENT_TYPE = "application/x-duper"
+JSON_CONTENT_TYPE = "application/json"
 
 
 T = TypeVar("T")
@@ -77,9 +78,11 @@ def DuperBody(model_type: type[T]) -> Any:  # pyright: ignore[reportExplicitAny,
     """
 
     async def _get_duper_body(request: Request) -> T:
-        if request.headers.get("Content-Type") not in (
+        content_type = request.headers.get("Content-Type")
+        if not content_type or content_type.split(";", 1)[0] not in (
             DUPER_CONTENT_TYPE,
             DUPER_ALT_CONTENT_TYPE,
+            JSON_CONTENT_TYPE,
         ):
             raise HTTPException(
                 status_code=status.HTTP_415_UNSUPPORTED_MEDIA_TYPE,
diff --git a/duper/Cargo.toml b/duper/Cargo.toml
index b426028..7032890 100644
--- a/duper/Cargo.toml
+++ b/duper/Cargo.toml
@@ -30,5 +30,5 @@ serde_core = { version = "1", optional = true }
 unicode-general-category = "1"
 
 [dev-dependencies]
-insta = "1.43.2"
+insta = "1.44.3"
 serde = { version = "1.0.228", features = ["derive"] }
diff --git a/duper_website/docs/spec.md b/duper_website/docs/spec.md
index 11154d1..53793c2 100644
--- a/duper_website/docs/spec.md
+++ b/duper_website/docs/spec.md
@@ -1,5 +1,5 @@
 ---
-version: "0.4.1"
+version: "0.4.2"
 ---
 
 <script setup lang="ts">
@@ -604,7 +604,7 @@ Duper files should use the extension `.duper`.
 
 When transferring Duper files over the internet, the appropriate MIME type is `application/duper`.
 
-Webservers should also accept the `application/x-duper` MIME type.
+Webservers should also accept the `application/x-duper` and `application/json` MIME types.
 
 ## W3C-EBNF grammar
 
diff --git a/duperfmt/Cargo.toml b/duperfmt/Cargo.toml
index 3b599c4..ce07825 100644
--- a/duperfmt/Cargo.toml
+++ b/duperfmt/Cargo.toml
@@ -20,3 +20,6 @@ topiary-core = "0.7"
 topiary-tree-sitter-facade = "0.7"
 tree-sitter = { version = "0.25", features = ["wasm"] }
 tree-sitter-duper = { version = "0.1", path = "../tree-sitter-duper" }
+
+[dev-dependencies]
+insta = "1.44.3"
diff --git a/duperfmt/src/lib.rs b/duperfmt/src/lib.rs
index 4fed9f3..1108126 100644
--- a/duperfmt/src/lib.rs
+++ b/duperfmt/src/lib.rs
@@ -36,3 +36,119 @@ pub fn format_duper(
         },
     )
 }
+
+#[cfg(test)]
+mod format_duper_tests {
+    use insta::assert_snapshot;
+
+    use super::{Tree, format_duper};
+
+    fn parse_duper(input: &'static str) -> Tree {
+        let mut parser = tree_sitter::Parser::new();
+        parser
+            .set_language(&tree_sitter_duper::LANGUAGE.into())
+            .unwrap();
+        let tree = parser.parse(input, None).expect("parser was initialized");
+        tree
+    }
+
+    #[test]
+    fn single_line_object_no_indent() {
+        let input = r#"
+            {level:"WARN",timestamp:Instant('2025-12-04T13:29:33.947380870-03:00'),target:"simple",span:{count:10,span_id:1},spans:[{count:10,span_id:1}],fields:{message:"too few gifts... try again later"}}
+        "#;
+        let tree = parse_duper(input);
+        let mut output = Vec::new();
+        format_duper(tree, input, &mut output, None, true).unwrap();
+        assert_snapshot!(String::from_utf8(output).unwrap());
+    }
+
+    #[test]
+    fn multiline_object_no_indent() {
+        let input = r##"
+            Product({
+                product_id: Uuid("1dd7b7aa-515e-405f-85a9-8ac812242609"),
+                name: "Wireless Bluetooth Headphones",
+                brand: "AudioTech", price: Decimal("129.99"), dimensions: (18.5, 15.2, 7.8), // In centimeters
+                weight: Kilograms(0.285),
+
+                in_stock: true,
+                specifications: {     battery_life  : Duration("30h"),
+                    noise_cancellation: true,
+                    connectivity: ["Bluetooth 5.0","3.5mm Jack"],
+                },
+                image_thumbnail: Png(b64"iVBORw0KGgoAAAANSUhEUgAAAGQ="),
+                tags:   
+                   [ "electronics" , "audio"  , "wireless" ],
+                release_date: PlainDate('2023-11-15'),
+                /* Warranty is optional */
+                "warranty period":null,
+                customer_ratings: {
+                    latest_review: r#"Absolutely ""astounding""!! 😎"#,
+                    average: 4.5,
+                    count: 127,
+                },
+                created_at: Instant('2023-11-17T21:50:43+00:00')
+                })
+        "##;
+        let tree = parse_duper(input);
+        let mut output = Vec::new();
+        format_duper(tree, input, &mut output, None, true).unwrap();
+        assert_snapshot!(String::from_utf8(output).unwrap());
+    }
+
+    #[test]
+    fn single_line_object_four_space_indent() {
+        let input = r#"
+            {level:"WARN",timestamp:Instant('2025-12-04T13:29:33.947380870-03:00'),target:"simple",span:{count:10,span_id:1},spans:[{count:10,span_id:1}],fields:{message:"too few gifts... try again later"}}
+        "#;
+        let tree = parse_duper(input);
+        let mut output = Vec::new();
+        format_duper(tree, input, &mut output, Some("    ".into()), true).unwrap();
+        assert_snapshot!(String::from_utf8(output).unwrap());
+    }
+
+    #[test]
+    fn multiline_object_four_space_indent() {
+        let input = r##"
+            Product({
+                product_id: Uuid("1dd7b7aa-515e-405f-85a9-8ac812242609"),
+                name: "Wireless Bluetooth Headphones",
+                brand: "AudioTech", price: Decimal("129.99"), dimensions: (18.5, 15.2, 7.8), // In centimeters
+                weight: Kilograms(0.285),
+
+                in_stock: true,
+                specifications: {     battery_life  : Duration("30h"),
+                    noise_cancellation: true,
+                    connectivity: ["Bluetooth 5.0","3.5mm Jack"],
+                },
+                image_thumbnail: Png(b64"iVBORw0KGgoAAAANSUhEUgAAAGQ="),
+                tags:   
+                   [ "electronics" , "audio"  , "wireless" ],
+                release_date: PlainDate('2023-11-15'),
+                /* Warranty is optional */
+                "warranty period":null,
+                customer_ratings: {
+                    latest_review: r#"Absolutely ""astounding""!! 😎"#,
+                    average: 4.5,
+                    count: 127,
+                },
+                created_at: Instant('2023-11-17T21:50:43+00:00')
+                })
+        "##;
+        let tree = parse_duper(input);
+        let mut output = Vec::new();
+        format_duper(tree, input, &mut output, Some("    ".into()), true).unwrap();
+        assert_snapshot!(String::from_utf8(output).unwrap());
+    }
+
+    #[test]
+    fn invalid_object() {
+        let input = r#"
+            {"_":
+        "#;
+        let tree = parse_duper(input);
+        let mut output = Vec::new();
+        assert!(format_duper(tree, input, &mut output, None, true).is_err());
+    }
+}
diff --git a/duperfmt/src/main.rs b/duperfmt/src/main.rs
index e114339..aab8aa5 100644
--- a/duperfmt/src/main.rs
+++ b/duperfmt/src/main.rs
@@ -81,14 +81,16 @@ fn main() -> miette::Result<()> {
     }
 
     // Read Duper
-    let (src, buf) = if let Some(file) = cli.file.as_ref() {
-        (file.to_string_lossy(), fs::read(file).into_diagnostic()?)
+    let (src, input) = if let Some(file) = cli.file.as_ref() {
+        (
+            file.to_string_lossy(),
+            fs::read_to_string(file).into_diagnostic()?,
+        )
     } else {
-        let mut buf = vec![];
-        io::stdin().read_to_end(&mut buf).into_diagnostic()?;
+        let mut buf = String::new();
+        io::stdin().read_to_string(&mut buf).into_diagnostic()?;
         (Cow::Borrowed("<stdin>"), buf)
     };
-    let input = String::from_utf8(buf).into_diagnostic()?;
 
     // Parse and check for errors
     let mut parser = tree_sitter::Parser::new();
diff --git a/duperfmt/src/snapshots/duperfmt__format_duper_tests__multiline_object_four_space_indent.snap b/duperfmt/src/snapshots/duperfmt__format_duper_tests__multiline_object_four_space_indent.snap
new file mode 100644
index 0000000..69a7d0c
--- /dev/null
+++ b/duperfmt/src/snapshots/duperfmt__format_duper_tests__multiline_object_four_space_indent.snap
@@ -0,0 +1,29 @@
+---
+source: duperfmt/src/lib.rs
+expression: "String::from_utf8(output).unwrap()"
+---
+Product({
+    product_id: Uuid("1dd7b7aa-515e-405f-85a9-8ac812242609"),
+    name: "Wireless Bluetooth Headphones",
+    brand: "AudioTech",
+    price: Decimal("129.99"),
+    dimensions: (18.5, 15.2, 7.8), // In centimeters
+    weight: Kilograms(0.285),
+    in_stock: true,
+    specifications: {
+        battery_life: Duration("30h"),
+        noise_cancellation: true,
+        connectivity: ["Bluetooth 5.0", "3.5mm Jack"],
+    },
+    image_thumbnail: Png(b64"iVBORw0KGgoAAAANSUhEUgAAAGQ="),
+    tags: ["electronics", "audio", "wireless"],
+    release_date: PlainDate('2023-11-15'),
+    /* Warranty is optional */
+    "warranty period": null,
+    customer_ratings: {
+        latest_review: r#"Absolutely ""astounding""!! 😎"#,
+        average: 4.5,
+        count: 127,
+    },
+    created_at: Instant('2023-11-17T21:50:43+00:00'),
+})
diff --git a/duperfmt/src/snapshots/duperfmt__format_duper_tests__multiline_object_no_indent.snap b/duperfmt/src/snapshots/duperfmt__format_duper_tests__multiline_object_no_indent.snap
new file mode 100644
index 0000000..9fb2d7d
--- /dev/null
+++ b/duperfmt/src/snapshots/duperfmt__format_duper_tests__multiline_object_no_indent.snap
@@ -0,0 +1,29 @@
+---
+source: duperfmt/src/lib.rs
+expression: "String::from_utf8(output).unwrap()"
+---
+Product({
+  product_id: Uuid("1dd7b7aa-515e-405f-85a9-8ac812242609"),
+  name: "Wireless Bluetooth Headphones",
+  brand: "AudioTech",
+  price: Decimal("129.99"),
+  dimensions: (18.5, 15.2, 7.8), // In centimeters
+  weight: Kilograms(0.285),
+  in_stock: true,
+  specifications: {
+    battery_life: Duration("30h"),
+    noise_cancellation: true,
+    connectivity: ["Bluetooth 5.0", "3.5mm Jack"],
+  },
+  image_thumbnail: Png(b64"iVBORw0KGgoAAAANSUhEUgAAAGQ="),
+  tags: ["electronics", "audio", "wireless"],
+  release_date: PlainDate('2023-11-15'),
+  /* Warranty is optional */
+  "warranty period": null,
+  customer_ratings: {
+    latest_review: r#"Absolutely ""astounding""!! 😎"#,
+    average: 4.5,
+    count: 127,
+  },
+  created_at: Instant('2023-11-17T21:50:43+00:00'),
+})
diff --git a/duperfmt/src/snapshots/duperfmt__format_duper_tests__single_line_object_four_space_indent.snap b/duperfmt/src/snapshots/duperfmt__format_duper_tests__single_line_object_four_space_indent.snap
new file mode 100644
index 0000000..721bdab
--- /dev/null
+++ b/duperfmt/src/snapshots/duperfmt__format_duper_tests__single_line_object_four_space_indent.snap
@@ -0,0 +1,5 @@
+---
+source: duperfmt/src/lib.rs
+expression: "String::from_utf8(output).unwrap()"
+---
+{level: "WARN", timestamp: Instant('2025-12-04T13:29:33.947380870-03:00'), target: "simple", span: {count: 10, span_id: 1}, spans: [{count: 10, span_id: 1}], fields: {message: "too few gifts... try again later"}}
diff --git a/duperfmt/src/snapshots/duperfmt__format_duper_tests__single_line_object_no_indent.snap b/duperfmt/src/snapshots/duperfmt__format_duper_tests__single_line_object_no_indent.snap
new file mode 100644
index 0000000..721bdab
--- /dev/null
+++ b/duperfmt/src/snapshots/duperfmt__format_duper_tests__single_line_object_no_indent.snap
@@ -0,0 +1,5 @@
+---
+source: duperfmt/src/lib.rs
+expression: "String::from_utf8(output).unwrap()"
+---
+{level: "WARN", timestamp: Instant('2025-12-04T13:29:33.947380870-03:00'), target: "simple", span: {count: 10, span_id: 1}, spans: [{count: 10, span_id: 1}], fields: {message: "too few gifts... try again later"}}
diff --git a/tree-sitter-duper/CHANGELOG.md b/tree-sitter-duper/CHANGELOG.md
index cb13827..491020a 100644
--- a/tree-sitter-duper/CHANGELOG.md
+++ b/tree-sitter-duper/CHANGELOG.md
@@ -4,7 +4,7 @@
 
 ### Added
 
-- Syntax highlighting query.
+- Add syntax highlighting query.
 
 ## 0.1.1 (2025-11-25)