Fix NoReverseMatch: Reverse for 'product_detail' with keyword arguments '{"slug": ""}' not found. in Django

This error means Django's URL resolver cannot find a URL pattern matching the given view name and arguments. Fix it by verifying the URL pattern name matches the reverse call, ensuring the arguments satisfy the URL regex or path converter, and checking that the app's urls.py is included in the root URL configuration.

Reading the Stack Trace

Here's what each line means:

• File "/app/products/templatetags/product_tags.py", line 12, in product_url: A custom template tag calls reverse() with an empty slug, which does not match the URL pattern requiring a non-empty slug.
• File "/venv/lib/python3.11/site-packages/django/urls/resolvers.py", line 828, in _reverse_with_prefix: Django tried all registered URL patterns but none matched the view name with the given empty slug argument.
• 1 pattern(s) tried: ['products/(?P<slug>[-\\w]+)/$']: The URL pattern requires a non-empty slug ([-\w]+ requires at least one character), but an empty string was passed.

Common Causes

# Product has an empty slug
product = Product.objects.create(name='Test', slug='')  # Empty slug

# In template:
{% url 'product_detail' slug=product.slug %}  # Fails with empty slug

# urls.py
urlpatterns = [
    path('products/<slug:slug>/', views.product_detail, name='product-detail'),
]

# template.html — wrong name (underscore vs hyphen)
{% url 'product_detail' slug=product.slug %}

# root urls.py
urlpatterns = [
    path('products/', include('products.urls', namespace='products')),
]

# template — missing namespace
{% url 'product_detail' slug=product.slug %}
# Should be: {% url 'products:product_detail' slug=product.slug %}

The Fix

Ensure the URL pattern name matches exactly what reverse() or {% url %} uses. Guard against empty slugs in templates, and auto-generate slugs in the model's save method to prevent empty values from reaching the database.

# urls.py
urlpatterns = [
    path('products/<slug:slug>/', views.product_detail, name='product-detail'),
]

# template.html
<a href="{% url 'product_detail' slug=product.slug %}">{{ product.name }}</a>

# urls.py
urlpatterns = [
    path('products/<slug:slug>/', views.product_detail, name='product_detail'),
]

# template.html
{% if product.slug %}
  <a href="{% url 'product_detail' slug=product.slug %}">{{ product.name }}</a>
{% endif %}

# models.py — ensure slug is never empty
class Product(models.Model):
    name = models.CharField(max_length=200)
    slug = models.SlugField(unique=True)

    def save(self, *args, **kwargs):
        if not self.slug:
            from django.utils.text import slugify
            self.slug = slugify(self.name)
        super().save(*args, **kwargs)

Testing the Fix

import pytest
from django.test import TestCase
from django.urls import reverse, NoReverseMatch
from products.models import Product


class TestProductURLs(TestCase):
    def setUp(self):
        self.product = Product.objects.create(name='Test Widget', slug='test-widget')

    def test_reverse_product_detail(self):
        url = reverse('product_detail', kwargs={'slug': 'test-widget'})
        assert url == '/products/test-widget/'

    def test_reverse_with_empty_slug_raises(self):
        with pytest.raises(NoReverseMatch):
            reverse('product_detail', kwargs={'slug': ''})

    def test_product_auto_generates_slug(self):
        product = Product.objects.create(name='New Gadget')
        assert product.slug == 'new-gadget'

    def test_product_detail_url_resolves(self):
        response = self.client.get(f'/products/{self.product.slug}/')
        assert response.status_code == 200

Run your tests:

pytest

Pushing Through CI/CD

git checkout -b fix/noreversematch-empty-slug,git add products/models.py products/urls.py templates/,git commit -m "fix: ensure URL name matches and slug is never empty",git push origin fix/noreversematch-empty-slug

Your CI config should look something like this:

name: CI
on:
  pull_request:
    branches: [main]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with:
          python-version: '3.11'
          cache: 'pip'
      - run: pip install -r requirements.txt
      - run: pytest --tb=short -q

The Full Manual Process: 18 Steps

Here's every step you just went through to fix this one bug:

1. Notice the error alert or see it in your monitoring tool
2. Open the error dashboard and read the stack trace
3. Identify the file and line number from the stack trace
4. Open your IDE and navigate to the file
5. Read the surrounding code to understand context
6. Reproduce the error locally
7. Identify the root cause
8. Write the fix
9. Run the test suite locally
10. Fix any failing tests
11. Write new tests covering the edge case
12. Run the full test suite again
13. Create a new git branch
14. Commit and push your changes
15. Open a pull request
16. Wait for code review
17. Merge and deploy to production
18. Monitor production to confirm the error is resolved

Total time: 30-60 minutes. For one bug.

pip install bugstack

import bugstack

bugstack.init(api_key=os.environ["BUGSTACK_API_KEY"])

Deploying the Fix (Manual Path)

1. Run the full test suite locally to confirm URL resolution works.
2. Open a pull request with the URL and model fixes.
3. Wait for CI checks to pass on the PR.
4. Have a teammate review and approve the PR.
5. Merge to main and verify all product links work correctly in staging.

Frequently Asked Questions