diff --git a/Cargo.toml b/Cargo.toml
index 267128a..678d4ef 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "openapi-lint"
 description = "Validate an OpenAPI schema against some rules"
-version = "0.4.0"
+version = "0.5.0"
 edition = "2021"
 license = "Apache-2.0"
 repository = "https://github.com/oxidecomputer/openapi-lint/"
diff --git a/README.md b/README.md
index 0f8750f..f18a6bf 100644
--- a/README.md
+++ b/README.md
@@ -200,4 +200,7 @@ easy to accidentally allow internally-relevant documentation leak out as
 externally-visible in the OpenAPI document. It's not possible to simply infer
 this from text alone, but we do look for shibboleths such as a Rust path
 delimeter (`::`) and bracketed expressions with no subsequent parentheses
-(`[title](http://link.dest)` being reasonable).
\ No newline at end of file
+(`[title](http://link.dest)` being reasonable).
+
+Additionally, operation summaries (the OpenAPI `summary` field) should be
+short phrases and **should not end with a period**.
diff --git a/src/lib.rs b/src/lib.rs
index 3fb5409..e453e36 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -70,6 +70,13 @@ impl Validator {
         let responses = spec
             .operations()
             .flat_map(|(_, _, op)| self.validate_operation_response(spec, op));
+        let op_summaries = if external {
+            spec.operations()
+                .filter_map(|path_method_op| self.validate_operation_summary(path_method_op))
+                .collect()
+        } else {
+            Vec::new()
+        };
         let op_docs = if external {
             spec.operations()
                 .flat_map(|(_, _, op)| op.description.as_ref().and_then(|s| check_doc_string(s)))
@@ -77,6 +84,7 @@ impl Validator {
         } else {
             Vec::new()
         };
+
         let named_schemas = spec.components.iter().flat_map(|components| {
             components
                 .schemas
@@ -90,6 +98,7 @@ impl Validator {
             .chain(parameters)
             .chain(responses)
             .chain(named_schemas)
+            .chain(op_summaries)
             .chain(op_docs)
             .collect()
     }
@@ -261,6 +270,31 @@ impl Validator {
         }
     }
 
+    fn validate_operation_summary(
+        &self,
+        path_method_op: (&str, &str, &Operation),
+    ) -> Option<String> {
+        let (path, method, op) = path_method_op;
+
+        const INFO: &str = "For more info, see \
+            https://github.com/oxidecomputer/openapi-lint#rust-documentation";
+
+        if let Some(summary) = &op.summary {
+            // summaries should be short phrases and should not end with a period
+            if summary.trim_end().ends_with('.') {
+                let operation_id = op.operation_id.as_deref().unwrap_or("<unknown>");
+                return Some(format!(
+                    "The operation for {} {} (operation_id: {}) has a summary \
+                    (first line of doc comment) that ends with a period; \
+                    summaries should not end with a period.\n{}",
+                    path, method, operation_id, INFO,
+                ));
+            }
+        }
+
+        None
+    }
+
     fn validate_operation_parameters(&self, spec: &OpenAPI, op: &Operation) -> Vec<String> {
         const INFO: &str = "For more info, see \
             https://github.com/oxidecomputer/openapi-lint#naming";
diff --git a/src/tests/errors.json b/src/tests/errors.json
index 64a1294..0d13661 100644
--- a/src/tests/errors.json
+++ b/src/tests/errors.json
@@ -48,6 +48,7 @@
     },
     "/hardware/racks": {
       "get": {
+        "summary": "List racks in the system.",
         "description": "List racks in the system.",
         "operationId": "hardware_racks_get",
         "parameters": [
diff --git a/src/tests/errors.out b/src/tests/errors.out
index d2cf460..4e1338e 100644
--- a/src/tests/errors.out
+++ b/src/tests/errors.out
@@ -5681,4 +5681,7 @@ The return type for unit_return was a trivial null.
 For more info, see https://github.com/oxidecomputer/openapi-lint#trivial-null-response
 
 The type "fake_id_sort_mode" has a name that is not PascalCase; to rename it add #[serde(rename = "FakeIdSortMode")]
-For more info, see https://github.com/oxidecomputer/openapi-lint#naming
\ No newline at end of file
+For more info, see https://github.com/oxidecomputer/openapi-lint#naming
+
+The operation for /hardware/racks get (operation_id: hardware_racks_get) has a summary (first line of doc comment) that ends with a period; summaries should not end with a period.
+For more info, see https://github.com/oxidecomputer/openapi-lint#rust-documentation
\ No newline at end of file