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TLDR:
  • Python’s CERTIFICATE_VERIFY_FAILED errors happen when your system can’t chain the server’s certificate back to a trusted root.
  • The safe fix is to update your system’s CA certificates — install certifi, or run Install Certificates.command on macOS.
  • Disabling SSL verification works as a development-only workaround but should never ship to production.

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The error

When a Python HTTP client connects to your Chainstack endpoint over HTTPS, it validates the server’s TLS certificate by chaining it back to a trusted root certificate authority. If your system’s CA bundle is outdated or missing, you’ll see errors like: 
[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate

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Update certifi (all OSes)

The certifi package ships Mozilla’s CA bundle for Python. Updating it covers most cases: 
pip install --upgrade certifi
If you use requests, urllib, aiohttp, or httpx, they pick up the updated bundle automatically the next time they construct a default SSL context.

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Install Certificates (macOS only)

Python installers on macOS don’t always install the system certificates. Run the bundled installer:
  1. Open Spotlight (Cmd + Space).
  2. Type Install Certificates.command and run it.
This installs certifi’s CA bundle into the Python you launched.

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Explicit certifi-aware context

If updating certifi alone doesn’t take effect, build the SSL context explicitly: 
import ssl
import certifi
from urllib.request import urlopen

url = "https://ethereum-mainnet.core.chainstack.com/AUTH_KEY"
context = ssl.create_default_context(cafile=certifi.where())
response = urlopen(url, context=context)

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Development-only workarounds

These workarounds disable certificate validation. Use only for local debugging — never in production. Skipping verification makes your connection vulnerable to man-in-the-middle attacks.

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Unverified ssl context

import ssl
import urllib.request

context = ssl._create_unverified_context()
urllib.request.urlopen(url, context=context)

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Override the default HTTPS context

import ssl

ssl._create_default_https_context = ssl._create_unverified_context

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requests with verify=False

import requests

requests.get(url, verify=False)

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See also

Last modified on May 19, 2026