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Let’s Encrypt provides rate limits to ensure fair usage by as many people as possible. We believe these rate limits are high enough to work for most people by default. We’ve also designed them so renewing a certificate almost never hits a rate limit, and so that large organizations can gradually increase the number of certificates they can issue without requiring intervention from Let’s Encrypt.
If you’re actively developing or testing a Let’s Encrypt client, please utilize our staging environment instead of the production API. If you’re working on integrating Let’s Encrypt as a provider or with a large website please review our Integration Guide.
The main limit is Certificates per Registered Domain (50 per week). A
registered domain is, generally speaking, the part of the domain you purchased
from your domain name registrar. For instance, in the name
the registered domain is
the registered domain is
example.co.uk. We use the
Public Suffix List to calculate the registered
If you have a lot of subdomains, you may want to combine them into a single certificate, up to a limit of 100 Names per Certificate. Combined with the above limit, that means you can issue certificates containing up to 5,000 unique subdomains per week. A certificate with multiple names is often called a SAN certificate, or sometimes a UCC certificate. Note: For performance and reliability reasons, it’s better to use fewer names per certificate whenever you can.
Renewals are treated specially: they don’t count against your Certificates per Registered Domain limit, but they are subject to a Duplicate Certificate limit of 5 per week. Note: renewals used to count against your Certificate per Registered Domain limit until March 2019, but they don’t anymore.
A certificate is considered a renewal (or a duplicate) of an earlier certificate if it contains
the exact same set of hostnames, ignoring capitalization and ordering of
hostnames. For instance, if you requested a certificate for the names
example.com], you could request four more certificates for
example.com] during the week. If you changed the set of hostnames
by adding [
blog.example.com], you would be able to request additional
Renewal handling ignores the public key and extensions requested. A certificate issuance can be considered a renewal even if you are using a new key.
Revoking certificates does not reset rate limits, because the resources used to issue those certificates have already been consumed.
There is a Failed Validation limit of 5 failures per account, per hostname, per hour. This limit is higher on our staging environment, so you can use that environment to debug connectivity problems.
The “new-reg”, “new-authz” and “new-cert” endpoints have an Overall Requests limit of 20 per second. The “/directory” endpoint and the “/acme” directory & subdirectories have an Overall Requests limit of 40 requests per second.
We have two other limits that you’re very unlikely to run into.
You can create a maximum of 10 Accounts per IP Address per 3 hours. You can create a maximum of 500 Accounts per IP Range within an IPv6 /48 per 3 hours. Hitting either account rate limit is very rare, and we recommend that large integrators prefer a design using one account for many customers.
You can have a maximum of 300 Pending Authorizations on your account. Hitting this rate limit is rare, and happens most often when developing ACME clients. It usually means that your client is creating authorizations and not fulfilling them. Please utilize our staging environment if you’re developing an ACME client.
If you’ve hit a rate limit, we don’t have a way to temporarily reset it. You’ll need to wait until the rate limit expires after a week. We use a sliding window, so if you issued 25 certificates on Monday and 25 more certificates on Friday, you’ll be able to issue again starting Monday. You can get a list of certificates issued for your registered domain by searching on crt.sh, which uses the public Certificate Transparency logs.
If you are a large hosting provider or organization working on a Let’s Encrypt integration, we have a rate limiting form that can be used to request a higher rate limit. It takes a few weeks to process requests, so this form is not suitable if you just need to reset a rate limit faster than it resets on its own.
Note that most hosting providers don’t need rate limit increases, because there’s no limit on the number of distinct registered domains for which you can issue. So long as most of your customers don’t have more than 2,000 subdomains on a registered domain, you most likely do not need an increase. See our Integration Guide for more advice.
If you have a large number of pending authorization objects and are getting a
rate limiting error, you can trigger a validation attempt for those
authorization objects by submitting a JWS-signed POST to one of its challenges, as
described in the
The pending authorization objects are represented by URLs of the form
https://acme-v01.api.letsencrypt.org/acme/authz/XYZ, and should show up in your
client logs. Note that it doesn’t matter whether validation succeeds or fails.
Either will take the authorization out of ‘pending’ state. If you do not
have logs containing the relevant authorization URLs, you need to wait for the
rate limit to expire. As described above, there is a sliding window, so this may
take less than a week depending on your pattern of issuance.
Note that having a large number of pending authorizations is generally the result of a buggy client. If you’re hitting this rate limit frequently you should double-check your client code.