Stanza allows users to access our Java toolkit, Stanford CoreNLP, via its server interface. Once the Java server is launched, Stanza can form requests for annotation in Python, and a Document-like object will be returned. You can find out more info about the full functionality of Stanford CoreNLP here.


  • Download the latest version of Stanford CoreNLP from here.
  • Download model files for the language you want to annotate from here and store them in the extracted CoreNLP folder.
  • Set the CORENLP_HOME environment variable to the location of the folder. Example: export CORENLP_HOME=/path/to/stanford-corenlp-full-2020-04-20.


After CoreNLP has been properly set up, you can start up the server and make requests in Python code with Stanza’s help. Below is a comprehensive example of starting a server, making requests, and accessing data from the returned Document object. We have also prepared a comprehensive Jupyter notebook tutorial, which you can experiment with interactively. By default, CoreNLP Client uses protobuf for message passing. A full definition of our protocols (a.k.a., our supported annotations) can be found here.

from stanza.server import CoreNLPClient

# example text
print('input text')

text = "Chris Manning is a nice person. Chris wrote a simple sentence. He also gives oranges to people."


# set up the client
print('starting up Java Stanford CoreNLP Server...')

# set up the client
with CoreNLPClient(annotators=['tokenize','ssplit','pos','lemma','ner', 'parse', 'depparse','coref'], timeout=30000, memory='16G') as client:
    # submit the request to the server
    ann = client.annotate(text)

    # get the first sentence
    sentence = ann.sentence[0]

    # get the constituency parse of the first sentence
    print('constituency parse of first sentence')
    constituency_parse = sentence.parseTree

    # get the first subtree of the constituency parse
    print('first subtree of constituency parse')

    # get the value of the first subtree
    print('value of first subtree of constituency parse')

    # get the dependency parse of the first sentence
    print('dependency parse of first sentence')
    dependency_parse = sentence.basicDependencies

    # get the first token of the first sentence
    print('first token of first sentence')
    token = sentence.token[0]

    # get the part-of-speech tag
    print('part of speech tag of token')

    # get the named entity tag
    print('named entity tag of token')

    # get an entity mention from the first sentence
    print('first entity mention in sentence')

    # access the coref chain
    print('coref chains for the example')

    # Use tokensregex patterns to find who wrote a sentence.
    pattern = '([ner: PERSON]+) /wrote/ /an?/ []{0,3} /sentence|article/'
    matches = client.tokensregex(text, pattern)
    # sentences contains a list with matches for each sentence.
    assert len(matches["sentences"]) == 3
    # length tells you whether or not there are any matches in this
    assert matches["sentences"][1]["length"] == 1
    # You can access matches like most regex groups.
    matches["sentences"][1]["0"]["text"] == "Chris wrote a simple sentence"
    matches["sentences"][1]["0"]["1"]["text"] == "Chris"

    # Use semgrex patterns to directly find who wrote what.
    pattern = '{word:wrote} >nsubj {}=subject >dobj {}=object'
    matches = client.semgrex(text, pattern)
    # sentences contains a list with matches for each sentence.
    assert len(matches["sentences"]) == 3
    # length tells you whether or not there are any matches in this
    assert matches["sentences"][1]["length"] == 1
    # You can access matches like most regex groups.
    matches["sentences"][1]["0"]["text"] == "wrote"
    matches["sentences"][1]["0"]["$subject"]["text"] == "Chris"
    matches["sentences"][1]["0"]["$object"]["text"] == "sentence"

    # Tregex example
    pattern = 'NP'
    matches = client.tregex(text, pattern)
    for match in matches:

Customizing Properties For Server Start And Requests

There are a variety of ways to set properties for the server at start time. Also, each request can have properties. For example, if your application may receive German or French input, you could start the server with the default German properties and you could send requests for French text with the default French properties, and alternate back and forth depending on the input text language. You could also imagine having one pipeline

For context, the Java server takes in requests, runs a StanfordCoreNLP pipeline, and sends a response. Annotators within a pipeline often use models to perform their work (e.g. a part-of-speech tagging model or a dependency parsing model). For efficiency, the server maintains two caches. One for the models (so they only have to be loaded once) and one for already built StanfordCoreNLP pipelines.

The server actually maintains two caches, one for the models, and one for pre-built Stanford CoreNLP pipelines. Loading models takes a significant amount of time (potentially on the order of a minute in some cases). But building a pipeline can also take some time (on the order of a half second). So throughput would be significantly impacted if pipelines were built per request. The server will keep around pipelines with particular configurations to avoid this penalty. The first request using a particular model or pipeline configuration will have delay associated with loading the model or building the pipeline. But future requests should not have this delay.

To avoid the first request having a long delay, one can use the preload option to load a set of models when the server launches.

Below are a collection of specific examples to demonstrate different ways to customize the server at start time or set specific properties for requests.

CoreNLP Client Options

During initialization, a CoreNLPClient object accepts the following options as arguments:

Option name Type Default Description
annotators str “tokenize,ssplit,lemma,pos,ner,depparse” The default list of CoreNLP annotators the server will use
properties - None See “Customize Server Start” section below
endpoint str http://localhost:9000 The host and port where the CoreNLP server will run on.
classpath str None Classpath to use for CoreNLP. None means $CORENLP_HOME, $CLASSPATH means to use the system $CLASSPATH, and otherwise, the given string is used
timeout int 15000 The maximum amount of time, in milliseconds, to wait for an annotation to finish before cancelling it.
threads int 5 The number of threads to hit the server with. If, for example, the server is running on an 8 core machine, you can specify this to be 8, and the client will allow you to make 8 simultaneous requests to the server.
output_format str “serialized” The default output format to use for the server response, unless otherwise specified. If set to be “serialized”, the response will be converted to local Python objects (see usage examples above). For a list of all supported output format, see the CoreNLP output options page.
memory str “4G” This specifies the memory used by the CoreNLP server process.
start_server bool True Whether to start the CoreNLP server when initializing the Python CoreNLPClient object. By default the CoreNLP server will be started using the provided options.
stdout file sys.stdout The standard output used by the CoreNLP server process.
stderr file sys.stderr The standard error used by the CoreNLP server process.
be_quiet bool True If set to False, the server process will print detailed error logs. Useful for diagnosing errors.
max_char_length int 100000 The max number of characters that will be accepted and processed by the CoreNLP server in a single request.
preload bool True Load the annotators immediately upon server start

Here is a quick example to specify which annotators to load and what output format to use

with CoreNLPClient(annotators='tokenize,ssplit,pos,lemma,ner', output_format='text') as client:

Customizing Server Start

When a CoreNLP Server is started it contains a set of default properties that define its default pipeline. This is the pipeline that will run unless the requests specify otherwise through request properties.

The following values can be supplied to the properties argument for CoreNLPClient’s init method to build a default pipeline:

Option Example Description
file path /path/to/server.props Path on the file system or CLASSPATH to a properties file
Stanford CoreNLP supported language french One of {arabic, chinese, english, french, german, spanish}, this will use Stanford CoreNLP defaults for that language
Python dictionary {‘annotators’: ‘tokenize,ssplit,pos’, ‘pos.model’: ‘/path/to/custom-model.ser.gz’} A Python dictionary specifying the properties, the properties will be written to a tmp file

If not using the file path or language name option, one can also specify which annotators to use and the desired outputFormat with the annotators and output_format args to CoreNLPClient’s init method.

Below are code examples to illustrate these different options:

You can start the server by specifying a properties file

with CoreNLPClient(properties='/path/to/server.props') as client:

Or, specifying a Stanford CoreNLP supported language

with CoreNLPClient(properties='french') as client:

Or, last but not least, specifying properties from a Python dictionary

with CoreNLPClient(properties={'annotators': 'tokenize,ssplit,pos', 'pos.model': '/path/to/custom-model.ser.gz'}) as client:

Stanford CoreNLP Server Settings

In addition to setting properties for the pipeline used by the Stanford CoreNLP server, there are also a variety of settings for the server itself. The table below describes these settings:

Option Description
server_id ID for the server, label attached to server’s shutdown key file
status_port port to server status check endpoints
uriContext URI context for server
strict obey strict HTTP standards
ssl if true, start server with (an insecure) SSL connection
key .jks file to load if ssl is enabled
username The username component of a username/password basic auth credential
password The password component of a username/password basic auth credential
preload load this list of annotators immediately at server launch
blacklist a list of IPv4 addresses to ban from using the server

All of these options can be set with CoreNLPClient’s init method.

There is more documention here for the server’s start up options.

Here is a quick example of specifying username and password for your server at launch

with CoreNLPClient(username='myusername', password='1234') as client:

If your CoreNLP server is password protected, here’s how you can supply that information to make sure annotation goes smoothly

ann = client.annotate(text, username='myusername', password='1234')

Request Properties

Properties for the StanfordCoreNLP pipeline run on text can be set for each request. If the request has properties, these will override the server’s defaults.

Request properties can be registered with Stanza’s CoreNLPClient to maximize efficiency. The client maintains a properties_cache to map keys to particular property settings. Alternatively, request properties can be specified as a Stanford CoreNLP support language to use the language defaults, or a full Python dictionary for maximal flexibility.

The following code examples below show examples of specifying request properties.

Here is an example of how to register a set of properties with the client’s properties_cache, and how to use those properties via the key for annotation

FRENCH_CUSTOM_PROPS = {'annotators': 'tokenize,ssplit,pos,parse', 'tokenize.language': 'fr',
                       'pos.model': 'edu/stanford/nlp/models/pos-tagger/french/french.tagger',
                       'parse.model': 'edu/stanford/nlp/models/lexparser/frenchFactored.ser.gz',
                       'outputFormat': 'text'}

with CoreNLPClient(annotators='tokenize,ssplit,pos') as client:
    client.register_properties_key('fr-custom', FRENCH_CUSTOM_PROPS)
    ann = client.annotate(text, properties_key='fr-custom')

Alternatively, request properties can simply be a language that you want to run the default CoreNLP pipeline for

ann = client.annotate(text, properties='german')

Or, a dictionary that specifies all properties you want to set/override

ann = client.annotate(text, properties=FRENCH_CUSTOM_PROPS)

Similarly to CoreNLPClient initialization, you can also specify the annotators and output format for CoreNLP for individual annotation requests

ann = client.annotate(text, properties=FRENCH_CUSTOM_PROPS, annotators='tokenize,ssplit,pos', output_format='json')