diff --git a/pyproject.toml b/pyproject.toml
index ecddda0..fc2e25b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "cosl"
-version = "0.0.48"
+version = "0.0.49"
 authors = [
     { name = "sed-i", email = "82407168+sed-i@users.noreply.github.com" },
 ]
diff --git a/src/cosl/rules.py b/src/cosl/rules.py
index 820aac0..b12adc9 100644
--- a/src/cosl/rules.py
+++ b/src/cosl/rules.py
@@ -75,8 +75,8 @@
 - `juju_application`
 """  # noqa: W505
 
+import hashlib
 import logging
-import os
 import re
 from abc import ABC, abstractmethod
 from pathlib import Path
@@ -86,11 +86,9 @@
 
 from . import CosTool, JujuTopology
 from .types import (
-    OfficialRuleFileFormat,
     OfficialRuleFileItem,
     QueryType,
     RuleType,
-    SingleRuleFormat,
 )
 
 logger = logging.getLogger(__name__)
@@ -149,7 +147,7 @@ def __init__(self, query_type: QueryType, topology: Optional[JujuTopology] = Non
         self.query_type = query_type
         self.topology = topology
         self.tool = CosTool(default_query_type=query_type)
-        self.groups = []  # type: List[Dict[str, Any]]
+        self.groups: List[OfficialRuleFileItem] = []
 
     @property
     @abstractmethod
@@ -160,7 +158,7 @@ def rule_type(self) -> RuleType:
     # --- HELPER METHODS FOR READING FILES, SHOULD BE STATIC --- #
 
     @staticmethod
-    def _is_official_rule_format(rules_dict: OfficialRuleFileFormat) -> bool:
+    def _is_official_rule_format(rules_dict: Dict[str, Any]) -> bool:
         """Are rules in the upstream format as supported by Prometheus or Loki.
 
         Rules in dictionary format are in "official" form if they
@@ -176,7 +174,7 @@ def _is_official_rule_format(rules_dict: OfficialRuleFileFormat) -> bool:
         return "groups" in rules_dict
 
     @staticmethod
-    def _is_single_rule_format(rules_dict: SingleRuleFormat, rule_type: RuleType) -> bool:
+    def _is_single_rule_format(rules_dict: Dict[str, Any], rule_type: RuleType) -> bool:
         """Are alert rules in single rule format.
 
         This library supports reading of rules in a custom format that
@@ -212,7 +210,7 @@ def _multi_suffix_glob(
         all_files_in_dir = dir_path.glob("**/*" if recursive else "*")
         return list(filter(lambda f: f.is_file() and f.suffix in suffixes, all_files_in_dir))
 
-    def _from_dir(self, dir_path: Path, recursive: bool) -> List[Dict[str, Any]]:
+    def _from_dir(self, dir_path: Path, recursive: bool) -> List[OfficialRuleFileItem]:
         """Read all rule files in a directory.
 
         All rules from files for the same directory are loaded into a single
@@ -227,7 +225,7 @@ def _from_dir(self, dir_path: Path, recursive: bool) -> List[Dict[str, Any]]:
             a list of dictionaries representing prometheus rule groups, each dictionary
             representing a group (structure determined by `yaml.safe_load`).
         """
-        groups = []  # type: List[Dict[str, Any]]
+        groups: List[OfficialRuleFileItem] = []
 
         # Gather all records into a list of groups
         for file_path in Rules._multi_suffix_glob(
@@ -243,7 +241,7 @@ def _from_dir(self, dir_path: Path, recursive: bool) -> List[Dict[str, Any]]:
     def _from_file(  # noqa: C901
         self, root_path: Path, file_path: Path
     ) -> List[OfficialRuleFileItem]:
-        """Read a rules file from path, injecting juju topology.
+        """Read a rules file from path.
 
         Args:
             root_path: full path to the root rules folder (used only for generating group name)
@@ -262,82 +260,96 @@ def _from_file(  # noqa: C901
                 logger.error("Failed to read rules from %s: %s", file_path.name, e)
                 return []
 
-            if not rule_file:
-                logger.warning("Empty rules file: %s", file_path.name)
-                return []
-            if not isinstance(rule_file, dict):
-                logger.error("Invalid rules file (must be a dict): %s", file_path.name)
-                return []
+            # Generate group name prefix
+            #  - name, from juju topology
+            #  - suffix, from the relative path of the rule file;
+            rel_path = file_path.parent.relative_to(root_path)
+            rel_path = "" if rel_path == Path(".") else str(rel_path)
+            group_name_parts = [self.topology.identifier] if self.topology else []
+            group_name_parts.append(rel_path)
+            group_name_prefix = "_".join(filter(None, group_name_parts))
 
-            if self._is_official_rule_format(cast(OfficialRuleFileFormat, rule_file)):
-                rule_file = cast(OfficialRuleFileFormat, rule_file)
-                groups = rule_file["groups"]
-            elif self._is_single_rule_format(cast(SingleRuleFormat, rule_file), self.rule_type):
-                # convert to list of groups
-                # group name is made up from the file name
-                rule_file = cast(SingleRuleFormat, rule_file)
-                groups = [{"name": file_path.stem, "rules": [rule_file]}]
-            else:
-                # invalid/unsupported
-                logger.error("Invalid rules file: %s", file_path.name)
+            try:
+                groups = self._from_dict(
+                    rule_file, group_name=file_path.stem, group_name_prefix=group_name_prefix
+                )
+            except ValueError as e:
+                logger.error("Invalid rules file: %s (%s)", file_path.name, e)
                 return []
 
-            # update rules with additional metadata
-            groups = cast(List[OfficialRuleFileItem], groups)
-            for group in groups:
-                if not self._is_already_modified(group["name"]):
-                    # update group name with topology and sub-path
-                    group["name"] = self._group_name(str(root_path), str(file_path), group["name"])
-
-                # add "juju_" topology labels
-                for rule in group["rules"]:
-                    if "labels" not in rule:
-                        rule["labels"] = {}
-
-                    if self.topology:
-                        # only insert labels that do not already exist
-                        for label, val in self.topology.label_matcher_dict.items():
-                            if label not in rule["labels"]:
-                                rule["labels"][label] = val
-
-                        # insert juju topology filters into a prometheus rule
-                        repl = r'job=~".+"' if self.query_type == "logql" else ""
-                        rule["expr"] = self.tool.inject_label_matchers(  # type: ignore
-                            expression=re.sub(r"%%juju_topology%%,?", repl, rule["expr"]),
-                            topology={
-                                k: rule["labels"][k]
-                                for k in ("juju_model", "juju_model_uuid", "juju_application")
-                                if rule["labels"].get(k) is not None
-                            },
-                            query_type=self.query_type,
-                        )
-
             return groups
 
-    def _group_name(self, root_path: str, file_path: str, group_name: str) -> str:
-        """Generate group name from path and topology.
-
-        The group name is made up of the relative path between the root dir_path, the file path,
-        and topology identifier.
+    def _from_dict(
+        self,
+        rule_dict: Dict[str, Any],
+        *,
+        group_name: Optional[str] = None,
+        group_name_prefix: Optional[str] = None,
+    ) -> List[OfficialRuleFileItem]:
+        """Process rules from dict, injecting juju topology. If a single-rule format is provided, a hash of the yaml file is injected into the group name to ensure uniqueness.
 
         Args:
-            root_path: path to the root rules dir.
-            file_path: path to rule file.
-            group_name: original group name to keep as part of the new augmented group name
+            rule_dict: rules content in single-rule or official-rule format as a YAML dict
+            group_name: a custom identifier for the rule name to include in the group name
+            group_name_prefix: a custom group identifier to prefix the resulting group name, likely Juju topology and relative path context
 
-        Returns:
-            New group name, augmented by juju topology and relative path.
+        Raises:
+            ValueError, when invalid rule format given.
         """
-        rel_path = os.path.relpath(os.path.dirname(file_path), root_path)
-        rel_path = "" if rel_path == "." else rel_path.replace(os.path.sep, "_")
+        if not rule_dict:
+            raise ValueError("Empty")
+
+        if self._is_official_rule_format(rule_dict):
+            groups = rule_dict["groups"]
+        elif self._is_single_rule_format(rule_dict, self.rule_type):
+            if not group_name:
+                # Note: the caller of this function should ensure this never happens:
+                # Either we use the standard format, or we'd pass a group_name.
+                # If/when we drop support for the single-rule-per-file format, this won't
+                # be needed anymore.
+                group_name = hashlib.shake_256(str(rule_dict).encode("utf-8")).hexdigest(10)
+
+            # convert to list of groups to match official rule format
+            groups = [{"name": group_name, "rules": [rule_dict]}]
+        else:
+            # invalid/unsupported
+            raise ValueError("Invalid rule format")
+
+        # update rules with additional metadata
+        groups = cast(List[OfficialRuleFileItem], groups)
+        for group in groups:
+            if not self._is_already_modified(group["name"]):
+                # update group name with topology and sub-path
+                group["name"] = "_".join(
+                    filter(None, [group_name_prefix, group["name"], f"{self.rule_type}s"])
+                )
+            # after sanitizing we should not modify group["name"] anymore
+            group["name"] = self._sanitize_metric_name(group["name"])
+
+            # add "juju_" topology labels
+            for rule in group["rules"]:
+                if "labels" not in rule:
+                    rule["labels"] = {}
+
+                if self.topology:
+                    # only insert labels that do not already exist
+                    for label, val in self.topology.label_matcher_dict.items():
+                        if label not in rule["labels"]:
+                            rule["labels"][label] = val
+
+                    # insert juju topology filters into a prometheus rule
+                    repl = r'job=~".+"' if self.query_type == "logql" else ""
+                    rule["expr"] = self.tool.inject_label_matchers(  # type: ignore
+                        expression=re.sub(r"%%juju_topology%%,?", repl, rule["expr"]),
+                        topology={
+                            k: rule["labels"][k]
+                            for k in ("juju_model", "juju_model_uuid", "juju_application")
+                            if rule["labels"].get(k) is not None
+                        },
+                        query_type=self.query_type,
+                    )
 
-        # Generate group name:
-        #  - name, from juju topology
-        #  - suffix, from the relative path of the rule file;
-        group_name_parts = [self.topology.identifier] if self.topology else []
-        group_name_parts.extend([rel_path, group_name, f"{self.rule_type}s"])
-        # filter to remove empty strings
-        return "_".join(filter(None, group_name_parts))
+        return groups
 
     def _is_already_modified(self, name: str) -> bool:
         """Detect whether a group name has already been modified with juju topology."""
@@ -346,8 +358,29 @@ def _is_already_modified(self, name: str) -> bool:
             return False
         return True
 
+    def _sanitize_metric_name(self, metric_name: str) -> str:
+        """Sanitize a metric name according to https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels."""
+        return "".join(char if re.match(r"[a-zA-Z0-9_:]", char) else "_" for char in metric_name)
+
     # ---- END STATIC HELPER METHODS --- #
 
+    def add(
+        self,
+        rule_dict: Dict[str, Any],
+        group_name: Optional[str] = None,
+        group_name_prefix: Optional[str] = None,
+    ) -> None:
+        """Add rules from dict to the existing ruleset.
+
+        Args:
+            rule_dict: a single-rule or official-rule YAML dict
+            group_name: a custom group name, used only if the new rule is of single-rule format
+            group_name_prefix: a custom group name prefix, used only if the new rule is of single-rule format
+        """
+        self.groups.extend(
+            self._from_dict(rule_dict, group_name=group_name, group_name_prefix=group_name_prefix)
+        )
+
     def add_path(self, dir_path: Union[str, Path], *, recursive: bool = False) -> None:
         """Add rules from a dir path.
 
@@ -357,9 +390,6 @@ def add_path(self, dir_path: Union[str, Path], *, recursive: bool = False) -> No
         Args:
             dir_path: either a rules file or a dir of rules files.
             recursive: whether to read files recursively or not (no impact if `path` is a file).
-
-        Returns:
-            True if path was added else False.
         """
         path = Path(dir_path) if isinstance(dir_path, str) else dir_path
         if path.is_dir():
diff --git a/tests/test_rules_promql.py b/tests/test_rules_promql.py
index afef8b8..38662e4 100644
--- a/tests/test_rules_promql.py
+++ b/tests/test_rules_promql.py
@@ -40,6 +40,7 @@ def test_each_alert_rule_is_topology_labeled(self):
                     self.assertIn("juju_application", labels)
                     self.assertIn("juju_model_uuid", labels)
                     # alerts should not have unit information if not already present
+                    # https://discourse.charmhub.io/t/juju-topology-labels/8874
                     self.assertNotIn("juju_unit", rule["labels"])
                     self.assertNotIn("juju_unit=", rule["expr"])
                 else:
@@ -76,6 +77,186 @@ def test_each_alert_expression_is_topology_labeled(self):
                 self.assertIn("juju_application", labels)
 
 
+class TestAddRuleFromStr(unittest.TestCase):
+    def setUp(self):
+        self.rule = {
+            "alert": "SomeRuleName",
+            "expr": "up < 1",
+            "labels": {"severity": "critical"},
+        }
+
+    def test_official_rule_add_alerts_from_dict(self):
+        official_rule = {
+            "groups": [
+                {
+                    "name": "SomeGroupName",
+                    "rules": [
+                        {
+                            "alert": "FooRule",
+                            "expr": "up < 1",
+                            "labels": {"severity": "critical"},
+                        },
+                        {
+                            "alert": "BarRule",
+                            "expr": "absent(up)",
+                            "labels": {"severity": "critical"},
+                        },
+                    ],
+                }
+            ]
+        }
+        expected_rules = {
+            "groups": [
+                {
+                    "name": "initial_alerts",
+                    "rules": [self.rule],
+                },
+                {"name": "SomeGroupName_alerts", "rules": official_rule["groups"][0]["rules"]},
+            ]
+        }
+        # GIVEN an alert rule
+        rules = AlertRules(query_type="promql")
+        rules.groups = rules._from_dict(self.rule, group_name="initial")
+        # WHEN a rule is added from string in official-rule format
+        rules.add(official_rule)
+        rules_dict = rules.as_dict()
+        # THEN the new rule is a combination of all
+        self.assertEqual({}, DeepDiff(expected_rules, rules_dict))
+
+    def test_single_rule_add_alerts_from_dict(self):
+        single_rule = {
+            "alert": "BarRule",
+            "expr": "up < 1",
+            "labels": {"severity": "critical"},
+        }
+        expected_rules = {
+            "groups": [
+                {
+                    "name": "initial_alerts",
+                    "rules": [self.rule],
+                },
+                {"name": "some_new_alerts", "rules": [single_rule]},
+            ]
+        }
+        # GIVEN an alert rule
+        rules = AlertRules(query_type="promql")
+        rules.groups = rules._from_dict(self.rule, group_name="initial")
+        # WHEN a rule is added from string in single-rule format with a custom group name and prefix
+        rules.add(
+            single_rule,
+            group_name="new",
+            group_name_prefix="some",
+        )
+        # THEN the new rule is a combination of all
+        rules_dict = rules.as_dict()
+        # AND the added rule group name has the custom group name and prefix
+        self.assertEqual({}, DeepDiff(expected_rules, rules_dict))
+
+
+class TestFromDictGroupName(unittest.TestCase):
+    def setUp(self):
+        self.official_rule = {
+            "groups": [
+                {
+                    "name": "SomeGroupName",
+                    "rules": [
+                        {
+                            "alert": "SomeRuleName",
+                            "expr": "up < 1",
+                            "labels": {"severity": "critical"},
+                        }
+                    ],
+                }
+            ]
+        }
+        self.single_rule = {
+            "alert": "SomeRuleName",
+            "expr": "up < 1",
+            "labels": {"severity": "critical"},
+        }
+
+    def test_single_rule_from_dict_group_sanitized(self):
+        # GIVEN an alert rule in single-rule format
+        rules = AlertRules(query_type="promql")
+        # WHEN processed as string and provided an illegal custom group name
+        groups = rules._from_dict(
+            self.single_rule, group_name="Foo$123/Hello:World(go_od)bye!@#^&*()[]{}|;:,.<>?`~_"
+        )
+        for group in groups:
+            # THEN the group name only contains characters in [a-zA-Z0-9_:]
+            # AND special characters are replaced with "_"
+            self.assertEqual(
+                group["name"], "Foo_123_Hello:World_go_od_bye______________:_________alerts"
+            )
+
+    def test_single_rule_from_dict(self):
+        # GIVEN an alert rule in single-rule format
+        rules = AlertRules(query_type="promql")
+        # WHEN processed as string
+        groups = rules._from_dict(self.single_rule)
+        for group in groups:
+            # THEN group name contains hash
+            self.assertNotEqual(get_hash(group["name"]), "")
+
+    def test_single_rule_from_dict_custom_group(self):
+        # GIVEN an alert rule in single-rule format
+        rules = AlertRules(query_type="promql")
+        # WHEN processed as string and provided custom group name
+        groups = rules._from_dict(self.single_rule, group_name="foo")
+        for group in groups:
+            # THEN group name does not contain hash
+            self.assertEqual(get_hash(group["name"]), "")
+            # AND group name contains the custom group name
+            self.assertIn("foo", group["name"])
+
+    def test_single_rule_from_dict_custom_group_prefix(self):
+        # GIVEN an alert rule in single-rule format
+        rules = AlertRules(query_type="promql")
+        # WHEN processed as string and provided custom group name prefix
+        groups = rules._from_dict(self.single_rule, group_name_prefix="foo")
+        for group in groups:
+            # THEN group name does not include the original group name
+            self.assertNotIn("SomeGroupName", group["name"])
+            # AND group name is prefixed with custom value
+            self.assertTrue(group["name"].startswith("foo"))
+
+    def test_official_rule_from_dict(self):
+        # GIVEN an alert rule in official-rule format
+        rules = AlertRules(query_type="promql")
+        # WHEN processed as dict
+        groups = rules._from_dict(self.official_rule)
+        for group in groups:
+            # THEN group name matches the group name in the alert
+            self.assertIn("SomeGroupName", group["name"])
+
+    def test_official_rule_from_dict_custom_group_prefix(self):
+        # GIVEN an alert rule in official-rule format
+        rules = AlertRules(query_type="promql")
+        # WHEN processed as string and provided custom group name prefix
+        groups = rules._from_dict(self.official_rule, group_name_prefix="foo")
+        for group in groups:
+            # THEN group name includes the original group name
+            self.assertIn("SomeGroupName", group["name"])
+            # AND group name is prefixed with custom value
+            self.assertTrue(group["name"].startswith("foo"))
+
+    def test_raises_value_error_empty_dict(self):
+        rules = AlertRules(query_type="promql")
+        with self.assertRaises(ValueError) as ctx:
+            rules._from_dict("")
+        self.assertEqual(str(ctx.exception), "Empty")
+
+    def test_raises_value_error_invalid_rule_format(self):
+        invalid_rule = {
+            "expr": "up < 1",
+            "labels": {"severity": "critical"},
+        }
+        rules = AlertRules(query_type="promql")
+        with self.assertRaises(ValueError) as ctx:
+            rules._from_dict(invalid_rule)
+        self.assertEqual(str(ctx.exception), "Invalid rule format")
+
+
 def sorted_matchers(matchers) -> str:
     parts = [m.strip() for m in matchers.split(",")]
     return ",".join(sorted(parts))
@@ -99,6 +280,27 @@ def expression_labels(expr):
         yield labels
 
 
+def get_hash(group_name: str) -> str:
+    """Extract the hash of the group name when a group name was not provided to _from_dict method in the Rules class.
+
+    This occurs when the single-rule format is provided rather than official-rule format.
+
+    Args:
+        group_name: a string representing the group name of the rules.
+
+    Returns:
+        the matching hexdigest of the group name if a match is found, otherwise an empty string.
+    """
+    import re
+
+    pattern = r"([a-f0-9]{20})_"
+    match = re.search(pattern, group_name)
+    if match:
+        return match.group(1)
+    else:
+        return ""
+
+
 class TestAlertRulesWithOneRulePerFile(unittest.TestCase):
     def setUp(self) -> None:
         free_standing_rule = {