A miniature version of Boulder, Pebble is a small ACME test server not suited for a production CA
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A miniature version of Boulder, Pebble is a small ACME test server not suited for use as a production CA.

!!! WARNING !!!


Pebble is NOT INTENDED FOR PRODUCTION USE. Pebble is for testing only.

By design Pebble will drop all of its state between invocations and will randomize keys/certificates used for issuance.


Pebble has several top level goals:

  1. Provide a simplified ACME testing front end
  2. Provide a test-bed for new and compatibility breaking ACME features
  3. Encourage ACME client best-practices
  4. Aggressively build in guardrails against non-testing usage

Pebble aims to address the need for ACME clients to have an easier to use, self-contained version of Boulder to test their clients against while developing ACME v2 support. Boulder is multi-process, requires heavy dependencies (MariaDB, gRPC, etc), and is operationally complex to integrate with other projects.

Where possible Pebble aims to be a test-bed for new ACME protocol features that can be used to inform later Boulder support. Pebble provides a way for Boulder developers to test compatibility breaking changes more aggressively than is appropriate for Boulder.

In places where the ACME specification allows customization/CA choice Pebble aims to make choices different from Boulder. For instance, Pebble changes the path structures for its resources and directory endpoints to differ from Boulder. The goal is to emphasize client specification compatibility and to avoid "over-fitting" on Boulder and the Let's Encrypt production service.

Lastly, Pebble will enforce it's test-only usage by aggressively building in guardrails that make using it in a production setting impossible or very inconvenient. Pebble will not support non-volatile storage or persistence between executions. Pebble will also randomize keys/certificates used for issuance. Where possible Pebble will make decisions that force clients to implement ACME correctly (e.g. randomizing /directory endpoint URLs to ensure clients are not hardcoding URLs.)


Pebble is missing some ACME features (PRs are welcome!). It does not presently support the "orders" field of account objects, subproblems, pre-authorization or external account binding. Pebble does not support revoking a certificate issued by a different ACME account by proving authorization of all of the certificate's domains.

Pebble does not perform all of the same input validation as Boulder. Some domain names that would be rejected by Boulder/Let's Encrypt may work with Pebble.

Pebble does not enforce any rate limits. It is not presently an appropriate tool for testing that your client handles Boulder/Let's Encrypt rate limits correctly.


  1. Set up Go and your $GOPATH
  2. go get -u github.com/letsencrypt/pebble/...
  3. cd $GOPATH/src/github.com/letsencrypt/pebble && go install ./...
  4. pebble -h



pebble -config ./test/config/pebble-config.json

Afterwards you can access the Pebble server's ACME directory at https://localhost:14000/dir.

Docker Image

With a docker-compose file:

version: '3'

  image: letsencrypt/pebble
  command: pebble -config ./test/my-pebble-config.json
    - 14000:14000
    - ./my-pebble-config.json:/test/my-pebble-config.json

With a Docker command:

docker run -e "PEBBLE_VA_NOSLEEP=1" letsencrypt/pebble
# or
docker run -e "PEBBLE_VA_NOSLEEP=1" --mount src=$(pwd)/my-pebble-config.json,target=/test/my-pebble-config.json,type=bind letsencrypt/pebble pebble -config /test/my-pebble-config.json

Note: The Pebble dockerfile uses multi-stage builds and requires Docker CE 17.05.0-ce or newer.

Strict Mode

Pebble's goal to aggressively support new protocol features and backwards compatibility breaking changes is slightly at odds with its goal to provide a simple, light-weight ACME test server for clients to use in integration tests. On the one hand we want to introduce breaking changes quickly and use Pebble as a test-bed for this. On the other we want to make sure we don't break client integration tests using Pebble too often.

As a balance to meet these two needs Pebble supports a -strict flag. By running Pebble with -strict false changes known to break client compatibility are disabled.

Presently we default -strict to false but this will change in the future. If you are using Pebble for integration tests and favour reliability over learning about breaking changes ASAP please explicitly run Pebble with -strict false.

DNS Server

By default Pebble uses the system DNS resolver, this may mean that caching causes problems with DNS-01 validation. It may also mean that no DNSSEC validation is performed. You should configure your system's recursive DNS resolver according to your needs or use the -dnsserver flag to define an address to a DNS server.

pebble -dnsserver
pebble -dnsserver
pebble -dnsserver :5053

Testing at full speed

By default Pebble will sleep a random number of seconds (from 0 to 15) between individual challenge validation attempts. This ensures clients don't make assumptions about when the challenge is solved from the CA side by observing a single request for a challenge response. Instead clients must poll the challenge to observe the state since the CA may send many validation requests.

To test issuance "at full speed" with no artificial sleeps set the environment variable PEBBLE_VA_NOSLEEP to 1. E.g.

PEBBLE_VA_NOSLEEP=1 pebble -config ./test/config/pebble-config.json

The maximal number of seconds to sleep can be configured by defining PEBBLE_VA_SLEEPTIME. It must be set to a positive integer.

Skipping Validation

If you want to avoid the hassle of having to stand up a challenge response server for real HTTP-01, DNS-01 or TLS-ALPN-01 validation requests Pebble supports a mode that always treats challenge validation requests as successful. By default this mode is disabled and challenge validation is performed.

To have all challenge POST requests succeed without performing any validation run:


Invalid Anti-Replay Nonce Errors

The urn:ietf:params:acme:error:badNonce error type is meant to be retry-able. When receiving this error a client should make a subsequent request to the /new-nonce endpoint (or use the nonce from the error response) to retry the failed request, rather than quitting outright.

Experience from Boulder indicates that many ACME clients do not gracefully retry on invalid nonce errors. To help ensure future ACME clients are able to gracefully handle these errors by default Pebble rejects 15% of all valid nonces as invalid.

The percentage of valid nonces that are rejected can be configured using the environment variable PEBBLE_WFE_NONCEREJECT. E.g. to reject 90% of good nonces as invalid instead of 15% run:


To never reject a valid nonce as invalid run:


Avoiding Client HTTPS Errors

By default Pebble is accessible over HTTPS-only and uses a test certificate generated using a test CA (See thetest/certs/ directory for more information).

Since the Pebble test CA isn't part of any default CA trust stores you must add the test/certs/pebble.minica.pem certificate to your client's trusted root configuration to avoid HTTPS errors. Your client should offer a runtime option to specify a list of trusted root CAs.

IMPORTANT: Do not add the pebble.minica.pem CA to the system-wide trust store or to any production systems/codebases. The private key for this CA is intentionally made publicly available in this repo.

CA Root Certificate

Note that the CA's root certificate is regenerated on every launch. It can be retrieved by a GET request to https://localhost:14000/root.

You might need the root certificate to verify the complete trust chain of generated certificates, for example in end-to-end tests.

IMPORTANT: Do not add Pebble's root or intermediate certificate to a trust store that you use for ordinary browsing or that is used for non-testing purposes, since Pebble and its generated keys are not audited or held to the same standards as the Let's Encrypt production CA and their keys, and so are not safe to use for anything other than testing. Also, their private keys will be lost as soon as the Pebble process terminates.