diff --git a/backend/Dockerfile b/backend/Dockerfile
index 9ae13260..413a5800 100644
--- a/backend/Dockerfile
+++ b/backend/Dockerfile
@@ -1,5 +1,10 @@
 FROM docker.io/library/python:3.12-slim
 
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends git \
+	&& apt-get purge -y --auto-remove \
+	&& rm -rf /var/lib/apt/lists/*
+
 WORKDIR /app
 
 ADD requirements.txt /app
diff --git a/backend/btrixcloud/crawlconfigs.py b/backend/btrixcloud/crawlconfigs.py
index 0f66f03e..aa2fd2bd 100644
--- a/backend/btrixcloud/crawlconfigs.py
+++ b/backend/btrixcloud/crawlconfigs.py
@@ -4,7 +4,7 @@ Crawl Config API handling
 
 # pylint: disable=too-many-lines
 
-from typing import List, Union, Optional, TYPE_CHECKING, cast
+from typing import List, Union, Optional, TYPE_CHECKING, cast, Dict, Tuple
 
 import asyncio
 import json
@@ -15,8 +15,9 @@ from datetime import datetime
 from uuid import UUID, uuid4
 import urllib.parse
 
-import pymongo
+import aiohttp
 from fastapi import APIRouter, Depends, HTTPException, Query
+import pymongo
 
 from .pagination import DEFAULT_PAGE_SIZE, paginated_format
 from .models import (
@@ -43,8 +44,9 @@ from .models import (
     CrawlConfigDeletedResponse,
     CrawlerProxy,
     CrawlerProxies,
+    ValidateCustomBehavior,
 )
-from .utils import dt_now, slug_from_name, validate_regexes
+from .utils import dt_now, slug_from_name, validate_regexes, is_url
 
 if TYPE_CHECKING:
     from .orgs import OrgOps
@@ -231,6 +233,10 @@ class CrawlConfigOps:
                 exclude = [exclude]
             validate_regexes(exclude)
 
+        if config_in.config.customBehaviors:
+            for url in config_in.config.customBehaviors:
+                self._validate_custom_behavior_url_syntax(url)
+
         now = dt_now()
         crawlconfig = CrawlConfig(
             id=uuid4(),
@@ -291,6 +297,23 @@ class CrawlConfigOps:
             execMinutesQuotaReached=exec_mins_quota_reached,
         )
 
+    def _validate_custom_behavior_url_syntax(self, url: str) -> Tuple[bool, List[str]]:
+        """Validate custom behaviors are valid URLs after removing custom git syntax"""
+        git_prefix = "git+"
+        is_git_repo = False
+
+        if url.startswith(git_prefix):
+            is_git_repo = True
+            url = url[len(git_prefix) :]
+
+        parts = url.split("?")
+        url = parts[0]
+
+        if not is_url(url):
+            raise HTTPException(status_code=400, detail="invalid_custom_behavior")
+
+        return is_git_repo, parts
+
     def ensure_quota_page_limit(self, crawlconfig: CrawlConfig, org: Organization):
         """ensure page limit is set to no greater than quota page limit, if any"""
         if org.quotas.maxPagesPerCrawl and org.quotas.maxPagesPerCrawl > 0:
@@ -356,6 +379,10 @@ class CrawlConfigOps:
                 exclude = [exclude]
             validate_regexes(exclude)
 
+        if update.config and update.config.customBehaviors:
+            for url in update.config.customBehaviors:
+                self._validate_custom_behavior_url_syntax(url)
+
         # indicates if any k8s crawl config settings changed
         changed = False
         changed = changed or (
@@ -1070,6 +1097,75 @@ class CrawlConfigOps:
                     flush=True,
                 )
 
+    async def _validate_behavior_git_repo(self, repo_url: str, branch: str = ""):
+        """Validate git repository and branch, if specified, exist and are reachable"""
+        cmd = f"git ls-remote {repo_url} HEAD"
+        proc = await asyncio.create_subprocess_shell(cmd)
+        if await proc.wait() > 0:
+            raise HTTPException(
+                status_code=404,
+                detail="custom_behavior_not_found",
+            )
+
+        if branch:
+            await asyncio.sleep(0.5)
+            git_remote_cmd = (
+                f"git ls-remote --exit-code --heads {repo_url} refs/heads/{branch}"
+            )
+            proc = await asyncio.create_subprocess_shell(git_remote_cmd)
+            if await proc.wait() > 0:
+                raise HTTPException(
+                    status_code=404,
+                    detail="custom_behavior_branch_not_found",
+                )
+
+    async def _validate_behavior_url(self, url: str):
+        """Validate behavior file exists at url"""
+        try:
+            timeout = aiohttp.ClientTimeout(total=10)
+            async with aiohttp.ClientSession(timeout=timeout) as session:
+                async with session.get(url) as resp:
+                    if resp.status >= 400:
+                        raise HTTPException(
+                            status_code=404,
+                            detail="custom_behavior_not_found",
+                        )
+        # pylint: disable=raise-missing-from
+        except aiohttp.ClientError:
+            raise HTTPException(
+                status_code=404,
+                detail="custom_behavior_not_found",
+            )
+
+    async def validate_custom_behavior(self, url: str) -> Dict[str, bool]:
+        """Validate custom behavior URL
+
+        Implemented:
+        - Ensure URL is valid (after removing custom git prefix and syntax)
+        - Ensure URL returns status code < 400
+        - Ensure git repository can be reached by git ls-remote and that branch
+        exists, if provided
+        """
+        git_branch = ""
+
+        is_git_repo, url_parts = self._validate_custom_behavior_url_syntax(url)
+        url = url_parts[0]
+
+        if is_git_repo and len(url_parts) > 1:
+            query_str = url_parts[1]
+            try:
+                git_branch = urllib.parse.parse_qs(query_str)["branch"][0]
+            # pylint: disable=broad-exception-caught
+            except (KeyError, IndexError):
+                pass
+
+        if is_git_repo:
+            await self._validate_behavior_git_repo(url, branch=git_branch)
+        else:
+            await self._validate_behavior_url(url)
+
+        return {"success": True}
+
 
 # ============================================================================
 # pylint: disable=too-many-locals
@@ -1316,6 +1412,14 @@ def init_crawl_config_api(
         asyncio.create_task(ops.re_add_all_scheduled_cron_jobs())
         return {"success": True}
 
+    @router.post("/validate/custom-behavior", response_model=SuccessResponse)
+    async def validate_custom_behavior(
+        behavior: ValidateCustomBehavior,
+        # pylint: disable=unused-argument
+        org: Organization = Depends(org_crawl_dep),
+    ):
+        return await ops.validate_custom_behavior(behavior.customBehavior)
+
     org_ops.router.include_router(router)
 
     return ops
diff --git a/backend/btrixcloud/models.py b/backend/btrixcloud/models.py
index 25014e2a..a3e1f2e7 100644
--- a/backend/btrixcloud/models.py
+++ b/backend/btrixcloud/models.py
@@ -333,6 +333,7 @@ class RawCrawlConfig(BaseModel):
 
     logging: Optional[str] = None
     behaviors: Optional[str] = "autoscroll,autoplay,autofetch,siteSpecific"
+    customBehaviors: List[str] = []
 
     userAgent: Optional[str] = None
 
@@ -541,6 +542,8 @@ class CrawlConfigDefaults(BaseModel):
 
     exclude: Optional[List[str]] = None
 
+    customBehaviors: List[str] = []
+
 
 # ============================================================================
 class CrawlConfigAddedResponse(BaseModel):
@@ -592,6 +595,13 @@ class CrawlConfigDeletedResponse(BaseModel):
     status: str
 
 
+# ============================================================================
+class ValidateCustomBehavior(BaseModel):
+    """Input model for validating custom behavior URL/Git reference"""
+
+    customBehavior: str
+
+
 # ============================================================================
 
 ### CRAWLER VERSIONS ###
diff --git a/backend/btrixcloud/utils.py b/backend/btrixcloud/utils.py
index 8e4b44fd..5b889655 100644
--- a/backend/btrixcloud/utils.py
+++ b/backend/btrixcloud/utils.py
@@ -11,6 +11,7 @@ import re
 
 from datetime import datetime, timezone
 from typing import Optional, Dict, Union, List, Any
+from urllib.parse import urlparse
 from uuid import UUID
 
 from fastapi import HTTPException
@@ -100,6 +101,15 @@ def is_falsy_bool(stri: Optional[str]) -> bool:
     return False
 
 
+def is_url(url: str) -> bool:
+    """Check if string is a valid URL"""
+    try:
+        result = urlparse(url)
+        return all([result.scheme, result.netloc])
+    except ValueError:
+        return False
+
+
 def str_list_to_bools(str_list: List[str], allow_none=True) -> List[Union[bool, None]]:
     """Return version of input string list cast to bool or None, ignoring other values"""
     output: List[Union[bool, None]] = []
diff --git a/backend/test/conftest.py b/backend/test/conftest.py
index b9a6e717..16617c79 100644
--- a/backend/test/conftest.py
+++ b/backend/test/conftest.py
@@ -326,7 +326,7 @@ def crawler_config_id_only(_crawler_create_config_only):
     return _crawler_config_id
 
 
-@pytest.fixture(scope="session")
+@pytest.fixture(scope="function")
 def sample_crawl_data():
     return {
         "runNow": False,
diff --git a/backend/test/test_crawlconfigs.py b/backend/test/test_crawlconfigs.py
index 14bdf6c8..b007eec6 100644
--- a/backend/test/test_crawlconfigs.py
+++ b/backend/test/test_crawlconfigs.py
@@ -543,3 +543,192 @@ def test_add_crawl_config_invalid_exclude_regex(
     )
     assert r.status_code == 400
     assert r.json()["detail"] == "invalid_regex"
+
+
+def test_add_crawl_config_custom_behaviors_invalid_url(
+    crawler_auth_headers, default_org_id, sample_crawl_data
+):
+    sample_crawl_data["config"]["customBehaviors"] = ["http"]
+    r = requests.post(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/",
+        headers=crawler_auth_headers,
+        json=sample_crawl_data,
+    )
+    assert r.status_code == 400
+    assert r.json()["detail"] == "invalid_custom_behavior"
+
+
+def test_add_crawl_config_custom_behaviors_valid_url(
+    crawler_auth_headers, default_org_id, sample_crawl_data
+):
+    url = "https://raw.githubusercontent.com/webrecorder/custom-behaviors/refs/heads/main/behaviors/fulcrum.js"
+    sample_crawl_data["config"]["customBehaviors"] = [url]
+    r = requests.post(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/",
+        headers=crawler_auth_headers,
+        json=sample_crawl_data,
+    )
+    assert r.status_code == 200
+    data = r.json()
+    config_id = data["id"]
+    assert config_id
+
+    r = requests.get(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/{config_id}",
+        headers=crawler_auth_headers,
+    )
+    assert r.status_code == 200
+    data = r.json()
+
+    assert data["id"] == config_id
+    assert data["config"]["customBehaviors"] == [url]
+
+
+def test_add_update_crawl_config_custom_behaviors_git_url(
+    crawler_auth_headers, default_org_id, sample_crawl_data
+):
+    git_url = "git+https://github.com/webrecorder/custom-behaviors"
+    git_url_with_params = (
+        "git+https://github.com/webrecorder/custom-behaviors?branch=main&path=behaviors"
+    )
+
+    # Create workflow and validate it looks like we expect
+    sample_crawl_data["config"]["customBehaviors"] = [git_url]
+    r = requests.post(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/",
+        headers=crawler_auth_headers,
+        json=sample_crawl_data,
+    )
+    assert r.status_code == 200
+    data = r.json()
+    config_id = data["id"]
+    assert config_id
+
+    r = requests.get(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/{config_id}",
+        headers=crawler_auth_headers,
+    )
+    assert r.status_code == 200
+    data = r.json()
+
+    assert data["id"] == config_id
+    assert data["config"]["customBehaviors"] == [git_url]
+
+    # Try to update custom behaviors with invalid url, validate unchanged
+    r = requests.patch(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/{config_id}/",
+        headers=crawler_auth_headers,
+        json={
+            "config": {
+                "customBehaviors": [git_url, "not-a-url"],
+            }
+        },
+    )
+    assert r.status_code == 400
+    assert r.json()["detail"] == "invalid_custom_behavior"
+
+    r = requests.get(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/{config_id}",
+        headers=crawler_auth_headers,
+    )
+    assert r.status_code == 200
+    data = r.json()
+
+    assert data["id"] == config_id
+    assert data["config"]["customBehaviors"] == [git_url]
+
+    # Update custom behaviors with valid url, validate changed
+    r = requests.patch(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/{config_id}/",
+        headers=crawler_auth_headers,
+        json={
+            "config": {
+                "customBehaviors": [git_url_with_params],
+            }
+        },
+    )
+    assert r.status_code == 200
+
+    r = requests.get(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/{config_id}",
+        headers=crawler_auth_headers,
+    )
+    assert r.status_code == 200
+    data = r.json()
+
+    assert data["id"] == config_id
+    assert data["config"]["customBehaviors"] == [git_url_with_params]
+
+
+def test_validate_custom_behavior(crawler_auth_headers, default_org_id):
+    valid_url = "https://raw.githubusercontent.com/webrecorder/custom-behaviors/refs/heads/main/behaviors/fulcrum.js"
+    invalid_url_404 = "https://webrecorder.net/nonexistent/behavior.js"
+    doesnt_resolve_url = "https://nonexistenturl-for-testing-browsertrix.com"
+    malformed_url = "http"
+
+    git_url = "git+https://github.com/webrecorder/custom-behaviors"
+    invalid_git_url = "git+https://github.com/webrecorder/doesntexist"
+    private_git_url = "git+https://github.com/webrecorder/website"
+
+    git_url_with_params = (
+        "git+https://github.com/webrecorder/custom-behaviors?branch=main&path=behaviors"
+    )
+    git_url_invalid_branch = (
+        "git+https://github.com/webrecorder/custom-behaviors?branch=doesntexist"
+    )
+
+    # Success
+    for url in (valid_url, git_url, git_url_with_params):
+        r = requests.post(
+            f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/validate/custom-behavior",
+            headers=crawler_auth_headers,
+            json={"customBehavior": url},
+        )
+        assert r.status_code == 200
+        assert r.json()["success"]
+
+    # Behavior 404s
+    for url in (invalid_url_404, doesnt_resolve_url):
+        r = requests.post(
+            f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/validate/custom-behavior",
+            headers=crawler_auth_headers,
+            json={"customBehavior": url},
+        )
+        assert r.status_code == 404
+        assert r.json()["detail"] == "custom_behavior_not_found"
+
+    # Malformed url
+    r = requests.post(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/validate/custom-behavior",
+        headers=crawler_auth_headers,
+        json={"customBehavior": malformed_url},
+    )
+    assert r.status_code == 400
+    assert r.json()["detail"] == "invalid_custom_behavior"
+
+    # Git repo doesn't exist
+    r = requests.post(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/validate/custom-behavior",
+        headers=crawler_auth_headers,
+        json={"customBehavior": invalid_git_url},
+    )
+    assert r.status_code == 404
+    assert r.json()["detail"] == "custom_behavior_not_found"
+
+    # Git repo isn't public
+    r = requests.post(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/validate/custom-behavior",
+        headers=crawler_auth_headers,
+        json={"customBehavior": private_git_url},
+    )
+    assert r.status_code == 404
+    assert r.json()["detail"] == "custom_behavior_not_found"
+
+    # Git branch doesn't exist
+    r = requests.post(
+        f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs/validate/custom-behavior",
+        headers=crawler_auth_headers,
+        json={"customBehavior": git_url_invalid_branch},
+    )
+    assert r.status_code == 404
+    assert r.json()["detail"] == "custom_behavior_branch_not_found"
diff --git a/backend/test/test_filter_sort_results.py b/backend/test/test_filter_sort_results.py
index bc40486a..fc104197 100644
--- a/backend/test/test_filter_sort_results.py
+++ b/backend/test/test_filter_sort_results.py
@@ -11,8 +11,8 @@ def test_get_config_by_created_by(crawler_auth_headers, default_org_id, crawler_
         f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs?userid={crawler_userid}",
         headers=crawler_auth_headers,
     )
-    assert len(r.json()["items"]) == 3
-    assert r.json()["total"] == 3
+    assert len(r.json()["items"]) == 5
+    assert r.json()["total"] == 5
 
 
 def test_get_config_by_modified_by(
@@ -23,8 +23,8 @@ def test_get_config_by_modified_by(
         f"{API_PREFIX}/orgs/{default_org_id}/crawlconfigs?modifiedBy={crawler_userid}",
         headers=crawler_auth_headers,
     )
-    assert len(r.json()["items"]) == 3
-    assert r.json()["total"] == 3
+    assert len(r.json()["items"]) == 5
+    assert r.json()["total"] == 5
 
 
 def test_get_configs_by_first_seed(
@@ -362,9 +362,9 @@ def test_sort_crawl_configs(
         headers=crawler_auth_headers,
     )
     data = r.json()
-    assert data["total"] == 9
+    assert data["total"] == 11
     items = data["items"]
-    assert len(items) == 9
+    assert len(items) == 11
 
     last_created = None
     for config in items:
diff --git a/backend/test/test_org.py b/backend/test/test_org.py
index 57c0b8fc..755e3711 100644
--- a/backend/test/test_org.py
+++ b/backend/test/test_org.py
@@ -60,7 +60,11 @@ def test_update_org_crawling_defaults(admin_auth_headers, default_org_id):
     r = requests.post(
         f"{API_PREFIX}/orgs/{default_org_id}/defaults/crawling",
         headers=admin_auth_headers,
-        json={"maxCrawlSize": 200000, "lang": "fr"},
+        json={
+            "maxCrawlSize": 200000,
+            "lang": "fr",
+            "customBehaviors": ["git+https://github.com/webrecorder/custom-behaviors"],
+        },
     )
 
     assert r.status_code == 200
@@ -72,6 +76,9 @@ def test_update_org_crawling_defaults(admin_auth_headers, default_org_id):
     assert data["crawlingDefaults"]
     assert data["crawlingDefaults"]["maxCrawlSize"] == 200000
     assert data["crawlingDefaults"]["lang"] == "fr"
+    assert data["crawlingDefaults"]["customBehaviors"] == [
+        "git+https://github.com/webrecorder/custom-behaviors"
+    ]
 
 
 def test_rename_org(admin_auth_headers, default_org_id):