diff --git a/crates/uv-requirements-txt/src/lib.rs b/crates/uv-requirements-txt/src/lib.rs
index a0a4fc2a3..d48c21386 100644
--- a/crates/uv-requirements-txt/src/lib.rs
+++ b/crates/uv-requirements-txt/src/lib.rs
@@ -47,7 +47,7 @@ use url::Url;
 
 #[cfg(feature = "http")]
 use uv_client::BaseClient;
-use uv_client::BaseClientBuilder;
+use uv_client::{BaseClientBuilder, Connectivity};
 use uv_configuration::{NoBinary, NoBuild, PackageNameSpecifier};
 use uv_distribution_types::{
     Requirement, UnresolvedRequirement, UnresolvedRequirementSpecification,
@@ -165,7 +165,7 @@ pub struct RequirementsTxt {
 }
 
 impl RequirementsTxt {
-    /// See module level documentation
+    /// See module level documentation.
     #[instrument(
         skip_all,
         fields(requirements_txt = requirements_txt.as_ref().as_os_str().to_str())
@@ -173,12 +173,11 @@ impl RequirementsTxt {
     pub async fn parse(
         requirements_txt: impl AsRef<Path>,
         working_dir: impl AsRef<Path>,
-        client_builder: &BaseClientBuilder<'_>,
     ) -> Result<Self, RequirementsTxtFileError> {
         Self::parse_with_cache(
             requirements_txt,
             working_dir,
-            client_builder,
+            &BaseClientBuilder::default().connectivity(Connectivity::Offline),
             &mut SourceCache::default(),
         )
         .await
@@ -209,6 +208,40 @@ impl RequirementsTxt {
         .await
     }
 
+    /// Parse requirements from a string, using the given path for error messages and resolving
+    /// relative paths.
+    pub async fn parse_str(
+        content: &str,
+        requirements_txt: impl AsRef<Path>,
+        working_dir: impl AsRef<Path>,
+        client_builder: &BaseClientBuilder<'_>,
+        source_contents: &mut SourceCache,
+    ) -> Result<Self, RequirementsTxtFileError> {
+        let requirements_txt = requirements_txt.as_ref();
+        let working_dir = working_dir.as_ref();
+        let requirements_dir = requirements_txt.parent().unwrap_or(working_dir);
+
+        let mut visited = VisitedFiles::Requirements {
+            requirements: &mut FxHashSet::default(),
+            constraints: &mut FxHashSet::default(),
+        };
+
+        Self::parse_inner(
+            content,
+            working_dir,
+            requirements_dir,
+            client_builder,
+            requirements_txt,
+            &mut visited,
+            source_contents,
+        )
+        .await
+        .map_err(|err| RequirementsTxtFileError {
+            file: requirements_txt.to_path_buf(),
+            error: err,
+        })
+    }
+
     /// See module level documentation
     #[instrument(
         skip_all,
@@ -1509,7 +1542,6 @@ mod test {
     use test_case::test_case;
     use unscanny::Scanner;
 
-    use uv_client::BaseClientBuilder;
     use uv_fs::Simplified;
 
     use crate::{RequirementsTxt, calculate_row_column};
@@ -1547,13 +1579,9 @@ mod test {
         let working_dir = workspace_test_data_dir().join("requirements-txt");
         let requirements_txt = working_dir.join(path);
 
-        let actual = RequirementsTxt::parse(
-            requirements_txt.clone(),
-            &working_dir,
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let actual = RequirementsTxt::parse(requirements_txt.clone(), &working_dir)
+            .await
+            .unwrap();
 
         let snapshot = format!("parse-{}", path.to_string_lossy());
 
@@ -1599,13 +1627,9 @@ mod test {
         let requirements_txt = temp_dir.path().join(path);
         fs::write(&requirements_txt, contents).unwrap();
 
-        let actual = RequirementsTxt::parse(
-            &requirements_txt,
-            &working_dir,
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let actual = RequirementsTxt::parse(&requirements_txt, &working_dir)
+            .await
+            .unwrap();
 
         let snapshot = format!("line-endings-{}", path.to_string_lossy());
 
@@ -1624,13 +1648,9 @@ mod test {
         let working_dir = workspace_test_data_dir().join("requirements-txt");
         let requirements_txt = working_dir.join(path);
 
-        let actual = RequirementsTxt::parse(
-            requirements_txt,
-            &working_dir,
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let actual = RequirementsTxt::parse(requirements_txt, &working_dir)
+            .await
+            .unwrap();
 
         let snapshot = format!("parse-unix-{}", path.to_string_lossy());
 
@@ -1649,13 +1669,9 @@ mod test {
         let working_dir = workspace_test_data_dir().join("requirements-txt");
         let requirements_txt = working_dir.join(path);
 
-        let actual = RequirementsTxt::parse(
-            requirements_txt,
-            &working_dir,
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let actual = RequirementsTxt::parse(requirements_txt, &working_dir)
+            .await
+            .unwrap_err();
 
         let snapshot = format!("parse-unix-{}", path.to_string_lossy());
 
@@ -1674,13 +1690,9 @@ mod test {
         let working_dir = workspace_test_data_dir().join("requirements-txt");
         let requirements_txt = working_dir.join(path);
 
-        let actual = RequirementsTxt::parse(
-            requirements_txt,
-            &working_dir,
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let actual = RequirementsTxt::parse(requirements_txt, &working_dir)
+            .await
+            .unwrap();
 
         let snapshot = format!("parse-windows-{}", path.to_string_lossy());
 
@@ -1700,13 +1712,9 @@ mod test {
             -r missing.txt
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error)
             .chain()
             // The last error is operating-system specific.
@@ -1745,13 +1753,9 @@ mod test {
             numpy[ö]==1.29
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -1778,13 +1782,9 @@ mod test {
             numpy @ https:///
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -1811,13 +1811,9 @@ mod test {
             -e https://localhost:8080/
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -1844,13 +1840,9 @@ mod test {
             -e https://files.pythonhosted.org/packages/f7/69/96766da2cdb5605e6a31ef2734aff0be17901cefb385b885c2ab88896d76/ruff-0.5.6.tar.gz
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -1875,13 +1867,9 @@ mod test {
             -e black[,abcdef]
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -1908,13 +1896,9 @@ mod test {
             --index-url 123
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -1939,13 +1923,9 @@ mod test {
             --index-url https:////
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -1971,13 +1951,9 @@ mod test {
             --no-binary
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -2004,13 +1980,9 @@ mod test {
             file.txt
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -2047,13 +2019,9 @@ mod test {
             -r subdir/child.txt
         "})?;
 
-        let requirements = RequirementsTxt::parse(
-            parent_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let requirements = RequirementsTxt::parse(parent_txt.path(), temp_dir.path())
+            .await
+            .unwrap();
 
         insta::with_settings!({
             filters => path_filters(&path_filter(temp_dir.path())),
@@ -2111,13 +2079,9 @@ mod test {
             --no-binary flask
         "})?;
 
-        let requirements = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let requirements = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap();
 
         insta::with_settings!({
             filters => path_filters(&path_filter(temp_dir.path())),
@@ -2186,13 +2150,9 @@ mod test {
             --no-index
         "})?;
 
-        let requirements = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let requirements = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap();
 
         insta::with_settings!({
             filters => path_filters(&path_filter(temp_dir.path())),
@@ -2288,13 +2248,9 @@ mod test {
             --index-url https://fake.pypi.org/simple
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -2336,13 +2292,9 @@ mod test {
             httpx # comment
         "})?;
 
-        let requirements = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let requirements = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap();
 
         insta::with_settings!({
             filters => path_filters(&path_filter(temp_dir.path())),
@@ -2551,13 +2503,9 @@ mod test {
             importlib_metadata-8.2.0+local-py3-none-any.whl[extra]
         "})?;
 
-        let requirements = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap();
+        let requirements = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap();
 
         insta::with_settings!({
             filters => path_filters(&path_filter(temp_dir.path())),
@@ -2893,13 +2841,9 @@ mod test {
             tqdm
         "})?;
 
-        let error = RequirementsTxt::parse(
-            requirements_txt.path(),
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await
-        .unwrap_err();
+        let error = RequirementsTxt::parse(requirements_txt.path(), temp_dir.path())
+            .await
+            .unwrap_err();
         let errors = anyhow::Error::new(error).chain().join("\n");
 
         let requirement_txt = regex::escape(&requirements_txt.path().user_display().to_string());
@@ -2995,12 +2939,7 @@ mod test {
             -c constraints-only-recursive.txt
         "})?;
 
-        let parsed = RequirementsTxt::parse(
-            &requirements,
-            temp_dir.path(),
-            &BaseClientBuilder::default(),
-        )
-        .await?;
+        let parsed = RequirementsTxt::parse(&requirements, temp_dir.path()).await?;
 
         let requirements: BTreeSet<String> = parsed
             .requirements
diff --git a/crates/uv-requirements/src/sources.rs b/crates/uv-requirements/src/sources.rs
index c148d5e77..5a725c24c 100644
--- a/crates/uv-requirements/src/sources.rs
+++ b/crates/uv-requirements/src/sources.rs
@@ -27,6 +27,9 @@ pub enum RequirementsSource {
     SetupCfg(PathBuf),
     /// Dependencies were provided via an unsupported Conda `environment.yml` file (e.g., `pip install -r environment.yml`).
     EnvironmentYml(PathBuf),
+    /// An extensionless file that could be either a PEP 723 script or a requirements.txt file.
+    /// We detect the format when reading the file.
+    Extensionless(PathBuf),
 }
 
 impl RequirementsSource {
@@ -50,7 +53,6 @@ impl RequirementsSource {
             .extension()
             .is_some_and(|ext| ext.eq_ignore_ascii_case("py") || ext.eq_ignore_ascii_case("pyw"))
         {
-            // TODO(blueraft): Support scripts without an extension.
             Ok(Self::Pep723Script(path))
         } else if path
             .extension()
@@ -60,6 +62,17 @@ impl RequirementsSource {
                 "`{}` is not a valid PEP 751 filename: expected TOML file to start with `pylock.` and end with `.toml` (e.g., `pylock.toml`, `pylock.dev.toml`)",
                 path.user_display(),
             ))
+        } else if path
+            .extension()
+            .is_some_and(|ext| ext.eq_ignore_ascii_case("txt") || ext.eq_ignore_ascii_case("in"))
+            || path.starts_with("http://")
+            || path.starts_with("https://")
+        {
+            Ok(Self::RequirementsTxt(path))
+        } else if path.extension().is_none() {
+            // If we don't have an extension, mark it as extensionless so we can detect
+            // the format later (either a PEP 723 script or a requirements.txt file).
+            Ok(Self::Extensionless(path))
         } else {
             Ok(Self::RequirementsTxt(path))
         }
@@ -302,7 +315,8 @@ impl std::fmt::Display for RequirementsSource {
             | Self::PyprojectToml(path)
             | Self::SetupPy(path)
             | Self::SetupCfg(path)
-            | Self::EnvironmentYml(path) => {
+            | Self::EnvironmentYml(path)
+            | Self::Extensionless(path) => {
                 write!(f, "{}", path.simplified_display())
             }
         }
diff --git a/crates/uv-requirements/src/specification.rs b/crates/uv-requirements/src/specification.rs
index e1e3fd1ec..c10feeaa1 100644
--- a/crates/uv-requirements/src/specification.rs
+++ b/crates/uv-requirements/src/specification.rs
@@ -46,7 +46,7 @@ use uv_fs::{CWD, Simplified};
 use uv_normalize::{ExtraName, PackageName, PipGroupName};
 use uv_pypi_types::PyProjectToml;
 use uv_requirements_txt::{RequirementsTxt, RequirementsTxtRequirement, SourceCache};
-use uv_scripts::{Pep723Error, Pep723Item, Pep723Script};
+use uv_scripts::{Pep723Error, Pep723Metadata, Pep723Script};
 use uv_warnings::warn_user;
 
 use crate::{RequirementsSource, SourceTree};
@@ -95,6 +95,142 @@ impl RequirementsSpecification {
         Self::from_source_with_cache(source, client_builder, &mut SourceCache::default()).await
     }
 
+    /// Create a [`RequirementsSpecification`] from PEP 723 script metadata.
+    fn from_pep723_metadata(metadata: &Pep723Metadata) -> Self {
+        let requirements = metadata
+            .dependencies
+            .as_ref()
+            .map(|dependencies| {
+                dependencies
+                    .iter()
+                    .map(|dependency| {
+                        UnresolvedRequirementSpecification::from(Requirement::from(
+                            dependency.to_owned(),
+                        ))
+                    })
+                    .collect::<Vec<UnresolvedRequirementSpecification>>()
+            })
+            .unwrap_or_default();
+
+        if let Some(tool_uv) = metadata.tool.as_ref().and_then(|tool| tool.uv.as_ref()) {
+            let constraints = tool_uv
+                .constraint_dependencies
+                .as_ref()
+                .map(|dependencies| {
+                    dependencies
+                        .iter()
+                        .map(|dependency| {
+                            NameRequirementSpecification::from(Requirement::from(
+                                dependency.to_owned(),
+                            ))
+                        })
+                        .collect::<Vec<NameRequirementSpecification>>()
+                })
+                .unwrap_or_default();
+
+            let overrides = tool_uv
+                .override_dependencies
+                .as_ref()
+                .map(|dependencies| {
+                    dependencies
+                        .iter()
+                        .map(|dependency| {
+                            UnresolvedRequirementSpecification::from(Requirement::from(
+                                dependency.to_owned(),
+                            ))
+                        })
+                        .collect::<Vec<UnresolvedRequirementSpecification>>()
+                })
+                .unwrap_or_default();
+
+            Self {
+                requirements,
+                constraints,
+                overrides,
+                index_url: tool_uv
+                    .top_level
+                    .index_url
+                    .as_ref()
+                    .map(|index| Index::from(index.clone()).url),
+                extra_index_urls: tool_uv
+                    .top_level
+                    .extra_index_url
+                    .as_ref()
+                    .into_iter()
+                    .flat_map(|urls| urls.iter().map(|index| Index::from(index.clone()).url))
+                    .collect(),
+                no_index: tool_uv.top_level.no_index.unwrap_or_default(),
+                find_links: tool_uv
+                    .top_level
+                    .find_links
+                    .as_ref()
+                    .into_iter()
+                    .flat_map(|urls| urls.iter().map(|index| Index::from(index.clone()).url))
+                    .collect(),
+                no_binary: NoBinary::from_args(
+                    tool_uv.top_level.no_binary,
+                    tool_uv
+                        .top_level
+                        .no_binary_package
+                        .clone()
+                        .unwrap_or_default(),
+                ),
+                no_build: NoBuild::from_args(
+                    tool_uv.top_level.no_build,
+                    tool_uv
+                        .top_level
+                        .no_build_package
+                        .clone()
+                        .unwrap_or_default(),
+                ),
+                ..Self::default()
+            }
+        } else {
+            Self {
+                requirements,
+                ..Self::default()
+            }
+        }
+    }
+
+    /// Create a [`RequirementsSpecification`] from a parsed `requirements.txt` file.
+    fn from_requirements_txt(requirements_txt: RequirementsTxt) -> Self {
+        Self {
+            requirements: requirements_txt
+                .requirements
+                .into_iter()
+                .map(UnresolvedRequirementSpecification::from)
+                .chain(
+                    requirements_txt
+                        .editables
+                        .into_iter()
+                        .map(UnresolvedRequirementSpecification::from),
+                )
+                .collect(),
+            constraints: requirements_txt
+                .constraints
+                .into_iter()
+                .map(Requirement::from)
+                .map(NameRequirementSpecification::from)
+                .collect(),
+            index_url: requirements_txt.index_url.map(IndexUrl::from),
+            extra_index_urls: requirements_txt
+                .extra_index_urls
+                .into_iter()
+                .map(IndexUrl::from)
+                .collect(),
+            no_index: requirements_txt.no_index,
+            find_links: requirements_txt
+                .find_links
+                .into_iter()
+                .map(IndexUrl::from)
+                .collect(),
+            no_binary: requirements_txt.no_binary,
+            no_build: requirements_txt.only_binary,
+            ..Self::default()
+        }
+    }
+
     /// Read the requirements and constraints from a source, using a cache for file contents.
     #[instrument(skip_all, level = tracing::Level::DEBUG, fields(source = % source))]
     pub async fn from_source_with_cache(
@@ -116,11 +252,7 @@ impl RequirementsSpecification {
                 ..Self::default()
             },
             RequirementsSource::RequirementsTxt(path) => {
-                if !(path == Path::new("-")
-                    || path.starts_with("http://")
-                    || path.starts_with("https://")
-                    || path.exists())
-                {
+                if !(path.starts_with("http://") || path.starts_with("https://") || path.exists()) {
                     return Err(anyhow::anyhow!("File not found: `{}`", path.user_display()));
                 }
 
@@ -128,50 +260,13 @@ impl RequirementsSpecification {
                     RequirementsTxt::parse_with_cache(path, &*CWD, client_builder, cache).await?;
 
                 if requirements_txt == RequirementsTxt::default() {
-                    if path == Path::new("-") {
-                        warn_user!("No dependencies found in stdin");
-                    } else {
-                        warn_user!(
-                            "Requirements file `{}` does not contain any dependencies",
-                            path.user_display()
-                        );
-                    }
+                    warn_user!(
+                        "Requirements file `{}` does not contain any dependencies",
+                        path.user_display()
+                    );
                 }
 
-                Self {
-                    requirements: requirements_txt
-                        .requirements
-                        .into_iter()
-                        .map(UnresolvedRequirementSpecification::from)
-                        .chain(
-                            requirements_txt
-                                .editables
-                                .into_iter()
-                                .map(UnresolvedRequirementSpecification::from),
-                        )
-                        .collect(),
-                    constraints: requirements_txt
-                        .constraints
-                        .into_iter()
-                        .map(Requirement::from)
-                        .map(NameRequirementSpecification::from)
-                        .collect(),
-                    index_url: requirements_txt.index_url.map(IndexUrl::from),
-                    extra_index_urls: requirements_txt
-                        .extra_index_urls
-                        .into_iter()
-                        .map(IndexUrl::from)
-                        .collect(),
-                    no_index: requirements_txt.no_index,
-                    find_links: requirements_txt
-                        .find_links
-                        .into_iter()
-                        .map(IndexUrl::from)
-                        .collect(),
-                    no_binary: requirements_txt.no_binary,
-                    no_build: requirements_txt.only_binary,
-                    ..Self::default()
-                }
+                Self::from_requirements_txt(requirements_txt)
             }
             RequirementsSource::PyprojectToml(path) => {
                 let contents = match fs_err::tokio::read_to_string(&path).await {
@@ -197,7 +292,7 @@ impl RequirementsSpecification {
             }
             RequirementsSource::Pep723Script(path) => {
                 let script = match Pep723Script::read(&path).await {
-                    Ok(Some(script)) => Pep723Item::Script(script),
+                    Ok(Some(script)) => script,
                     Ok(None) => {
                         return Err(anyhow::anyhow!(
                             "`{}` does not contain inline script metadata",
@@ -213,106 +308,7 @@ impl RequirementsSpecification {
                     Err(err) => return Err(err.into()),
                 };
 
-                let metadata = script.metadata();
-
-                let requirements = metadata
-                    .dependencies
-                    .as_ref()
-                    .map(|dependencies| {
-                        dependencies
-                            .iter()
-                            .map(|dependency| {
-                                UnresolvedRequirementSpecification::from(Requirement::from(
-                                    dependency.to_owned(),
-                                ))
-                            })
-                            .collect::<Vec<UnresolvedRequirementSpecification>>()
-                    })
-                    .unwrap_or_default();
-
-                if let Some(tool_uv) = metadata.tool.as_ref().and_then(|tool| tool.uv.as_ref()) {
-                    let constraints = tool_uv
-                        .constraint_dependencies
-                        .as_ref()
-                        .map(|dependencies| {
-                            dependencies
-                                .iter()
-                                .map(|dependency| {
-                                    NameRequirementSpecification::from(Requirement::from(
-                                        dependency.to_owned(),
-                                    ))
-                                })
-                                .collect::<Vec<NameRequirementSpecification>>()
-                        })
-                        .unwrap_or_default();
-
-                    let overrides = tool_uv
-                        .override_dependencies
-                        .as_ref()
-                        .map(|dependencies| {
-                            dependencies
-                                .iter()
-                                .map(|dependency| {
-                                    UnresolvedRequirementSpecification::from(Requirement::from(
-                                        dependency.to_owned(),
-                                    ))
-                                })
-                                .collect::<Vec<UnresolvedRequirementSpecification>>()
-                        })
-                        .unwrap_or_default();
-
-                    Self {
-                        requirements,
-                        constraints,
-                        overrides,
-                        index_url: tool_uv
-                            .top_level
-                            .index_url
-                            .as_ref()
-                            .map(|index| Index::from(index.clone()).url),
-                        extra_index_urls: tool_uv
-                            .top_level
-                            .extra_index_url
-                            .as_ref()
-                            .into_iter()
-                            .flat_map(|urls| {
-                                urls.iter().map(|index| Index::from(index.clone()).url)
-                            })
-                            .collect(),
-                        no_index: tool_uv.top_level.no_index.unwrap_or_default(),
-                        find_links: tool_uv
-                            .top_level
-                            .find_links
-                            .as_ref()
-                            .into_iter()
-                            .flat_map(|urls| {
-                                urls.iter().map(|index| Index::from(index.clone()).url)
-                            })
-                            .collect(),
-                        no_binary: NoBinary::from_args(
-                            tool_uv.top_level.no_binary,
-                            tool_uv
-                                .top_level
-                                .no_binary_package
-                                .clone()
-                                .unwrap_or_default(),
-                        ),
-                        no_build: NoBuild::from_args(
-                            tool_uv.top_level.no_build,
-                            tool_uv
-                                .top_level
-                                .no_build_package
-                                .clone()
-                                .unwrap_or_default(),
-                        ),
-                        ..Self::default()
-                    }
-                } else {
-                    Self {
-                        requirements,
-                        ..Self::default()
-                    }
-                }
+                Self::from_pep723_metadata(&script.metadata)
             }
             RequirementsSource::SetupPy(path) => {
                 if !path.is_file() {
@@ -350,6 +346,39 @@ impl RequirementsSpecification {
                     path.user_display()
                 ));
             }
+            RequirementsSource::Extensionless(path) => {
+                // Read the file content.
+                let content = if let Some(content) = cache.get(path.as_path()) {
+                    content.clone()
+                } else {
+                    let content = uv_fs::read_to_string_transcode(&path).await?;
+                    cache.insert(path.clone(), content.clone());
+                    content
+                };
+
+                // Detect if it's a PEP 723 script.
+                if let Some(metadata) = Pep723Metadata::parse(content.as_bytes())? {
+                    Self::from_pep723_metadata(&metadata)
+                } else {
+                    // If it's not a PEP 723 script, assume it's a `requirements.txt` file.
+                    let requirements_txt =
+                        RequirementsTxt::parse_str(&content, &path, &*CWD, client_builder, cache)
+                            .await?;
+
+                    if requirements_txt == RequirementsTxt::default() {
+                        if path == Path::new("-") {
+                            warn_user!("No dependencies found in stdin");
+                        } else {
+                            warn_user!(
+                                "Requirements file `{}` does not contain any dependencies",
+                                path.user_display()
+                            );
+                        }
+                    }
+
+                    Self::from_requirements_txt(requirements_txt)
+                }
+            }
         })
     }
 
diff --git a/crates/uv-requirements/src/upgrade.rs b/crates/uv-requirements/src/upgrade.rs
index 473dfe8e1..443f9c429 100644
--- a/crates/uv-requirements/src/upgrade.rs
+++ b/crates/uv-requirements/src/upgrade.rs
@@ -2,7 +2,6 @@ use std::path::Path;
 
 use anyhow::Result;
 
-use uv_client::{BaseClientBuilder, Connectivity};
 use uv_configuration::Upgrade;
 use uv_fs::CWD;
 use uv_git::ResolvedRepositoryReference;
@@ -38,13 +37,7 @@ pub async fn read_requirements_txt(
     }
 
     // Parse the requirements from the lockfile.
-    let requirements_txt = RequirementsTxt::parse(
-        output_file,
-        &*CWD,
-        // Pseudo-client for reading local-only requirements.
-        &BaseClientBuilder::default().connectivity(Connectivity::Offline),
-    )
-    .await?;
+    let requirements_txt = RequirementsTxt::parse(output_file, &*CWD).await?;
 
     // Map each entry in the lockfile to a preference.
     let preferences = requirements_txt
diff --git a/crates/uv/src/commands/project/add.rs b/crates/uv/src/commands/project/add.rs
index 0e1e95406..8de79428d 100644
--- a/crates/uv/src/commands/project/add.rs
+++ b/crates/uv/src/commands/project/add.rs
@@ -138,6 +138,7 @@ pub(crate) async fn add(
             RequirementsSource::Package(_)
             | RequirementsSource::Editable(_)
             | RequirementsSource::RequirementsTxt(_)
+            | RequirementsSource::Extensionless(_)
             | RequirementsSource::EnvironmentYml(_) => {}
         }
     }
diff --git a/crates/uv/src/commands/project/run.rs b/crates/uv/src/commands/project/run.rs
index e64fe62b5..16053de23 100644
--- a/crates/uv/src/commands/project/run.rs
+++ b/crates/uv/src/commands/project/run.rs
@@ -140,7 +140,7 @@ hint: If you are running a script with `{}` in the shebang, you may need to incl
             RequirementsSource::SetupCfg(_) => {
                 bail!("Adding requirements from a `setup.cfg` is not supported in `uv run`");
             }
-            RequirementsSource::RequirementsTxt(path) => {
+            RequirementsSource::Extensionless(path) => {
                 if path == Path::new("-") {
                     requirements_from_stdin = true;
                 }
diff --git a/crates/uv/tests/it/edit.rs b/crates/uv/tests/it/edit.rs
index 759fbfaa6..b8b8ad831 100644
--- a/crates/uv/tests/it/edit.rs
+++ b/crates/uv/tests/it/edit.rs
@@ -7096,6 +7096,62 @@ fn add_script_without_metadata_table_with_docstring() -> Result<()> {
     Ok(())
 }
 
+/// Add to a script without a `.py` extension.
+#[test]
+fn add_extensionless_script() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let script = context.temp_dir.child("script");
+    script.write_str(indoc! {r#"
+        #!/usr/bin/env python3
+        # /// script
+        # requires-python = ">=3.12"
+        # dependencies = []
+        # ///
+        import requests
+        from rich.pretty import pprint
+
+        resp = requests.get("https://peps.python.org/api/peps.json")
+        data = resp.json()
+        pprint([(k, v["title"]) for k, v in data.items()][:10])
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.add().args(["rich", "requests<3"]).arg("--script").arg("script"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Updated `script`
+    "###);
+
+    let script_content = context.read("script");
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            script_content, @r###"
+        #!/usr/bin/env python3
+        # /// script
+        # requires-python = ">=3.12"
+        # dependencies = [
+        #     "requests<3",
+        #     "rich",
+        # ]
+        # ///
+        import requests
+        from rich.pretty import pprint
+
+        resp = requests.get("https://peps.python.org/api/peps.json")
+        data = resp.json()
+        pprint([(k, v["title"]) for k, v in data.items()][:10])
+        "###
+        );
+    });
+    Ok(())
+}
+
 /// Remove a dependency that is present in multiple places.
 #[test]
 fn remove_repeated() -> Result<()> {
diff --git a/crates/uv/tests/it/tool_run.rs b/crates/uv/tests/it/tool_run.rs
index 07396b596..6f0babcd9 100644
--- a/crates/uv/tests/it/tool_run.rs
+++ b/crates/uv/tests/it/tool_run.rs
@@ -2646,8 +2646,7 @@ fn tool_run_with_incompatible_build_constraints() -> Result<()> {
 fn tool_run_with_dependencies_from_script() -> Result<()> {
     let context = TestContext::new("3.12").with_filtered_counts();
 
-    let script = context.temp_dir.child("script.py");
-    script.write_str(indoc! {r#"
+    let script_contents = indoc! {r#"
         # /// script
         # requires-python = ">=3.11"
         # dependencies = [
@@ -2656,7 +2655,13 @@ fn tool_run_with_dependencies_from_script() -> Result<()> {
         # ///
 
         import anyio
-    "#})?;
+    "#};
+
+    let script = context.temp_dir.child("script.py");
+    script.write_str(script_contents)?;
+
+    let script_without_extension = context.temp_dir.child("script-no-ext");
+    script_without_extension.write_str(script_contents)?;
 
     // script dependencies (anyio) are now installed.
     uv_snapshot!(context.filters(), context.tool_run()
@@ -2684,6 +2689,20 @@ fn tool_run_with_dependencies_from_script() -> Result<()> {
      + sniffio==1.3.1
     ");
 
+    uv_snapshot!(context.filters(), context.tool_run()
+        .arg("--with-requirements")
+        .arg("script-no-ext")
+        .arg("black")
+        .arg("script-no-ext")
+        .arg("-q"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved [N] packages in [TIME]
+    ");
+
     // Error when the script is not a valid PEP723 script.
     let script = context.temp_dir.child("not_pep723_script.py");
     script.write_str("import anyio")?;