diff --git a/tests/harness/src/output/parameter.rs b/tests/harness/src/output/parameter.rs
index 87c143218..d01e2b634 100644
--- a/tests/harness/src/output/parameter.rs
+++ b/tests/harness/src/output/parameter.rs
@@ -29,16 +29,28 @@ impl ParamList {
     }
 }
 
-#[derive(Clone, Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize, Eq, PartialEq, Ord, PartialOrd)]
 #[serde(rename_all = "PascalCase")]
 pub struct Param {
     pub name: String,
     pub value: String,
-    pub raw: String,
+    pub raw: Option<String>,
+    #[serde(rename = "Modified At")]
+    pub modified_at: Option<String>,
+    #[serde(rename = "Created At")]
+    pub created_at: Option<String>,
 }
 
 pub trait ParseParamListExt {
     fn parse_param_list(&self) -> ParamList;
+    fn get_param(&self, name: &str) -> Option<Param> {
+        let mut params = self.parse_param_list();
+        let (index, _) = params
+            .iter()
+            .enumerate()
+            .find(|(_, param)| param.name == name)?;
+        Some(params.swap_remove(index))
+    }
 }
 
 impl ParseParamListExt for assert_cmd::assert::Assert {
diff --git a/tests/test_parameters.rs b/tests/test_parameters.rs
index 4767cdac1..de50eac1c 100644
--- a/tests/test_parameters.rs
+++ b/tests/test_parameters.rs
@@ -1,5 +1,5 @@
 use cloudtruth_config::{CT_ENVIRONMENT, CT_PROJECT};
-use cloudtruth_test_harness::prelude::*;
+use cloudtruth_test_harness::{output::parameter::ParseParamListExt, prelude::*};
 use indoc::{formatdoc, indoc};
 use maplit::hashmap;
 
@@ -1090,3 +1090,157 @@ fn test_parameters_pagination() {
         .success()
         .paginated(PAGE_SIZE);
 }
+
+#[test]
+#[use_harness]
+fn test_parameters_as_of_tag() {
+    let proj = Project::with_prefix("param-tags").create();
+    let env = Environment::with_prefix("param-tags").create();
+    let mut envs = hashmap! {
+        CT_PROJECT => proj.name().as_str(),
+        CT_ENVIRONMENT => env.name().as_str()
+    };
+    cloudtruth!("param set param1 --value original")
+        .envs(&envs)
+        .assert()
+        .success();
+    let param1 = cloudtruth!("param list --show-times -f json")
+        .envs(&envs)
+        .assert()
+        .success()
+        .get_param("param1")
+        .unwrap();
+    cloudtruth!("param set param1 --value updated")
+        .envs(&envs)
+        .assert()
+        .success();
+    let param2 = cloudtruth!("param list --show-times -f json")
+        .envs(&envs)
+        .assert()
+        .success()
+        .get_param("param1")
+        .unwrap();
+    cloudtruth!("env tag set {env} my-tag --desc 'quick tag'")
+        .envs(&envs)
+        .assert()
+        .success();
+    cloudtruth!("param set param1 --value final")
+        .envs(&envs)
+        .assert()
+        .success();
+    let result = cloudtruth!("param list --show-times -f json --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .success()
+        .get_param("param1")
+        .unwrap();
+    assert_eq!(result, param2);
+    let modified_at = param1.modified_at.as_deref().unwrap();
+    let result = cloudtruth!("param list --show-times -f json --as-of '{modified_at}'")
+        .envs(&envs)
+        .assert()
+        .success()
+        .get_param("param1")
+        .unwrap();
+    assert_eq!(result, param1);
+    cloudtruth!("env tag set {env} my-tag --time '2021-01-20'")
+        .envs(&envs)
+        .assert()
+        .success();
+    cloudtruth!("param ls -v --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains("No ProjectLedger matches the given query"));
+    cloudtruth!("param diff --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains("No ProjectLedger matches the given query"));
+    cloudtruth!("param env param1 --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains("No ProjectLedger matches the given query"));
+    cloudtruth!("param export docker --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains("No ProjectLedger matches the given query"));
+    cloudtruth!("param get param1 --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains("No ProjectLedger matches the given query"));
+    cloudtruth!("param ls -v --as-of no-such-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains!(
+            "Tag `no-such-tag` could not be found in environment `{env}`"
+        ));
+    cloudtruth!("param diff --as-of no-such-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains!(
+            "Tag `no-such-tag` could not be found in environment `{env}`"
+        ));
+    cloudtruth!("param env param1 --as-of no-such-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains!(
+            "Tag `no-such-tag` could not be found in environment `{env}`"
+        ));
+    cloudtruth!("param export docker --as-of no-such-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains!(
+            "Tag `no-such-tag` could not be found in environment `{env}`"
+        ));
+    cloudtruth!("param get param1 --as-of no-such-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains!(
+            "Tag `no-such-tag` could not be found in environment `{env}`"
+        ));
+    envs.insert(CT_ENVIRONMENT, "default");
+    cloudtruth!("param ls -v --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains(
+            "Tag `my-tag` could not be found in environment `default`",
+        ));
+    cloudtruth!("param diff --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains(
+            "Tag `my-tag` could not be found in environment `default`",
+        ));
+    cloudtruth!("param env param1 --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains(
+            "Tag `my-tag` could not be found in environment `default`",
+        ));
+    cloudtruth!("param export docker --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains(
+            "Tag `my-tag` could not be found in environment `default`",
+        ));
+    cloudtruth!("param get param1 --as-of my-tag")
+        .envs(&envs)
+        .assert()
+        .failure()
+        .stderr(contains(
+            "Tag `my-tag` could not be found in environment `default`",
+        ));
+}
diff --git a/tests/test_templates.rs b/tests/test_templates.rs
index f67442890..2e566bc7c 100644
--- a/tests/test_templates.rs
+++ b/tests/test_templates.rs
@@ -1037,7 +1037,10 @@ fn test_templates_ref_by_param() {
         .expect("Could not find parameter 'my_parameter'");
     assert_eq!(&param.name, "my_parameter");
     assert_eq!(&param.value, "nothing to evaluate here");
-    assert_eq!(param.raw, format!("{{{{ cloudtruth.templates.{temp} }}}}"));
+    assert_eq!(
+        param.raw,
+        Some(format!("{{{{ cloudtruth.templates.{temp} }}}}"))
+    );
 
     cloudtruth!("template del -y {temp}")
         .envs(&vars)
@@ -1083,7 +1086,10 @@ fn test_templates_ref_by_param() {
         .find_by_name("param1")
         .expect("Could not find parameter 'param1'");
     assert_eq!("new-param-name = sample value", param.value);
-    assert_eq!(format!("{{{{ cloudtruth.templates.{temp} }}}}"), param.raw);
+    assert_eq!(
+        Some(format!("{{{{ cloudtruth.templates.{temp} }}}}")),
+        param.raw
+    );
 }
 
 #[test]