REST API

The MLflow REST API allows you to create, list, and get experiments and runs, and log parameters, metrics, and artifacts. The API is hosted under the /api route on the MLflow tracking server. For example, to list experiments on a tracking server hosted at http://localhost:5000, access http://localhost:5000/api/2.0/preview/mlflow/experiments/list.


Create Experiment

Endpoint HTTP Method
2.0/mlflow/experiments/create POST

Create an experiment with a name. Returns the ID of the newly created experiment. Validates that another experiment with the same name does not already exist and fails if another experiment with the same name already exists.

Throws RESOURCE_ALREADY_EXISTS if a experiment with the given name exists.

Request Structure

Field Name Type Description
name STRING Experiment name. This field is required.
artifact_location STRING Location where all artifacts for the experiment are stored. If not provided, the remote server will select an appropriate default.

Response Structure

Field Name Type Description
experiment_id STRING Unique identifier for the experiment.

List Experiments

Endpoint HTTP Method
2.0/mlflow/experiments/list GET

Get a list of all experiments.

Request Structure

Field Name Type Description
view_type ViewType Qualifier for type of experiments to be returned. If unspecified, return only active experiments.

Response Structure

Field Name Type Description
experiments An array of Experiment All experiments.

Get Experiment

Endpoint HTTP Method
2.0/mlflow/experiments/get GET

Get metadata for an experiment and a list of runs for the experiment. This method works on deleted experiments.

Request Structure

Field Name Type Description
experiment_id STRING ID of the associated experiment. This field is required.

Response Structure

Field Name Type Description
experiment Experiment Experiment details.
runs An array of RunInfo All (max limit to be imposed) active runs associated with this experiment.

Delete Experiment

Endpoint HTTP Method
2.0/mlflow/experiments/delete POST

Mark an experiment and associated metadata, runs, metrics, params, and tags for deletion. If the experiment uses FileStore, artifacts associated with experiment are also deleted.

Request Structure

Field Name Type Description
experiment_id STRING ID of the associated experiment. This field is required.

Restore Experiment

Endpoint HTTP Method
2.0/mlflow/experiments/restore POST

Restore an experiment marked for deletion. This also restores associated metadata, runs, metrics, params, and tags. If experiment uses FileStore, underlying artifacts associated with experiment are also restored.

Throws RESOURCE_DOES_NOT_EXIST if experiment was never created or was permanently deleted.

Request Structure

Field Name Type Description
experiment_id STRING ID of the associated experiment. This field is required.

Update Experiment

Endpoint HTTP Method
2.0/mlflow/experiments/update POST

Update experiment metadata.

Request Structure

Field Name Type Description
experiment_id STRING ID of the associated experiment. This field is required.
new_name STRING If provided, the experiment’s name is changed to the new name. The new name must be unique.

Create Run

Endpoint HTTP Method
2.0/mlflow/runs/create POST

Create a new run within an experiment. A run is usually a single execution of a machine learning or data ETL pipeline. MLflow uses runs to track Param, Metric, and RunTag associated with a single execution.

Request Structure

Field Name Type Description
experiment_id STRING ID of the associated experiment.
user_id STRING ID of the user executing the run. This field is deprecated as of MLflow 1.0, and will be removed in a future MLflow release. Use ‘mlflow.user’ tag instead.
start_time INT64 Unix timestamp in milliseconds of when the run started.
tags An array of RunTag Additional metadata for run.

Response Structure

Field Name Type Description
run Run The newly created run.

Delete Run

Endpoint HTTP Method
2.0/mlflow/runs/delete POST

Mark a run for deletion.

Request Structure

Field Name Type Description
run_id STRING ID of the run to delete. This field is required.

Restore Run

Endpoint HTTP Method
2.0/mlflow/runs/restore POST

Restore a deleted run.

Request Structure

Field Name Type Description
run_id STRING ID of the run to restore. This field is required.

Get Run

Endpoint HTTP Method
2.0/mlflow/runs/get GET

Get metadata, metrics, params, and tags for a run. In the case where multiple metrics with the same key are logged for a run, return only the value with the latest timestamp. If there are multiple values with the latest timestamp, return the maximum of these values.

Request Structure

Field Name Type Description
run_id STRING ID of the run to fetch. Must be provided.
run_uuid STRING [Deprecated, use run_id instead] ID of the run to fetch. This field will be removed in a future MLflow version.

Response Structure

Field Name Type Description
run Run Run metadata (name, start time, etc) and data (metrics, params, and tags).

Log Metric

Endpoint HTTP Method
2.0/mlflow/runs/log-metric POST

Log a metric for a run. A metric is a key-value pair (string key, float value) with an associated timestamp. Examples include the various metrics that represent ML model accuracy. A metric can be logged multiple times.

Request Structure

Field Name Type Description
run_id STRING ID of the run under which to log the metric. Must be provided.
run_uuid STRING [Deprecated, use run_id instead] ID of the run under which to log the metric. This field will be removed in a future MLflow version.
key STRING Name of the metric. This field is required.
value DOUBLE Double value of the metric being logged. This field is required.
timestamp INT64 Unix timestamp in milliseconds at the time metric was logged. This field is required.
step INT64 Step at which to log the metric

Log Batch

Endpoint HTTP Method
2.0/mlflow/runs/log-batch POST

Log a batch of metrics, params, and tags for a run. If any data failed to be persisted, the server will respond with an error (non-200 status code). In case of error (due to internal server error or an invalid request), partial data may be written.

You can write metrics, params, and tags in interleaving fashion, but within a given entity type are guaranteed to follow the order specified in the request body. That is, for an API request like

{
   "run_id": "2a14ed5c6a87499199e0106c3501eab8",
   "metrics": [
     {"key": "mae", "value": 2.5, "timestamp": 1552550804},
     {"key": "rmse", "value": 2.7, "timestamp": 1552550804},
   ],
   "params": [
     {"key": "model_class", "value": "LogisticRegression"},
   ]
}

the server is guaranteed to write metric “rmse” after “mae”, though it may write param “model_class” before both metrics, after “mae”, or after both metrics.

The overwrite behavior for metrics, params, and tags is as follows:

  • Metrics: metric values are never overwritten. Logging a metric (key, value, timestamp) appends to the set of values for the metric with the provided key.
  • Tags: tag values can be overwritten by successive writes to the same tag key. That is, if multiple tag values with the same key are provided in the same API request, the last-provided tag value is written. Logging the same tag (key, value) is permitted - that is, logging a tag is idempotent.
  • Params: once written, param values cannot be changed (attempting to overwrite a param value will result in an error). However, logging the same param (key, value) is permitted - that is, logging a param is idempotent.

Request Limits

A single JSON-serialized API request may be up to 1 MB in size and contain:

  • No more than 1000 metrics, params, and tags in total
  • Up to 1000 metrics
  • Up to 100 params
  • Up to 100 tags

For example, a valid request might contain 900 metrics, 50 params, and 50 tags, but logging 900 metrics, 50 params, and 51 tags is invalid. The following limits also apply to metric, param, and tag keys and values:

  • Metric, param, and tag keys can be up to 250 characters in length
  • Param and tag values can be up to 250 characters in length

Request Structure

Field Name Type Description
run_id STRING ID of the run to log under
metrics An array of Metric Metrics to log. A single request can contain up to 1000 metrics, and up to 1000 metrics, params, and tags in total.
params An array of Param Params to log. A single request can contain up to 100 params, and up to 1000 metrics, params, and tags in total.
tags An array of RunTag Tags to log. A single request can contain up to 100 tags, and up to 1000 metrics, params, and tags in total.

Set Tag

Endpoint HTTP Method
2.0/mlflow/runs/set-tag POST

Set a tag on a run. Tags are run metadata that can be updated during a run and after a run completes.

Request Structure

Field Name Type Description
run_id STRING ID of the run under which to log the tag. Must be provided.
run_uuid STRING [Deprecated, use run_id instead] ID of the run under which to log the tag. This field will be removed in a future MLflow version.
key STRING Name of the tag. Maximum size is 255 bytes. This field is required.
value STRING String value of the tag being logged. Maximum size is 5000 bytes. This field is required.

Log Param

Endpoint HTTP Method
2.0/mlflow/runs/log-parameter POST

Log a param used for a run. A param is a key-value pair (string key, string value). Examples include hyperparameters used for ML model training and constant dates and values used in an ETL pipeline. A param can be logged only once for a run.

Request Structure

Field Name Type Description
run_id STRING ID of the run under which to log the param. Must be provided.
run_uuid STRING [Deprecated, use run_id instead] ID of the run under which to log the param. This field will be removed in a future MLflow version.
key STRING Name of the param. Maximum size is 255 bytes. This field is required.
value STRING String value of the param being logged. Maximum size is 500 bytes. This field is required.

Get Metric History

Endpoint HTTP Method
2.0/mlflow/metrics/get-history GET

Get a list of all values for the specified metric for a given run.

Request Structure

Field Name Type Description
run_id STRING ID of the run from which to fetch metric values. Must be provided.
run_uuid STRING [Deprecated, use run_id instead] ID of the run from which to fetch metric values. This field will be removed in a future MLflow version.
metric_key STRING Name of the metric. This field is required.

Response Structure

Field Name Type Description
metrics An array of Metric All logged values for this metric.

Search Runs

Endpoint HTTP Method
2.0/mlflow/runs/search POST

Search for runs that satisfy expressions. Search expressions can use Metric and Param keys.

Request Structure

Field Name Type Description
experiment_ids An array of STRING List of experiment IDs to search over.
filter STRING

A filter expression over params, metrics, and tags, that allows returning a subset of runs. The syntax is a subset of SQL that supports ANDing together binary operations between a param, metric, or tag and a constant.

Example: metrics.rmse < 1 and params.model_class = 'LogisticRegression'

You can select columns with special characters (hyphen, space, period, etc.) by using double quotes: metrics."model class" = 'LinearRegression' and tags."user-name" = 'Tomas'

Supported operators are =, !=, >, >=, <, and <=.

You cannot provide filter when anded_expressions is present; an INVALID_PARAMETER_VALUE error will be returned if both are specified. If both filter and anded_expressions are absent, all runs part of the given experiments are returned.

run_view_type ViewType Whether to display only active, only deleted, or all runs. Defaults to only active runs.
max_results INT32 Maximum number of runs desired. Max threshold is 50000
order_by An array of STRING Ordering expressions like “tags.`model class` DESC”

Response Structure

Field Name Type Description
runs An array of Run Runs that match the search criteria.

List Artifacts

Endpoint HTTP Method
2.0/mlflow/artifacts/list GET

List artifacts for a run. Takes an optional artifact_path prefix which if specified, the response contains only artifacts with the specified prefix.

Request Structure

Field Name Type Description
run_id STRING ID of the run whose artifacts to list. Must be provided.
run_uuid STRING [Deprecated, use run_id instead] ID of the run whose artifacts to list. This field will be removed in a future MLflow version.
path STRING Filter artifacts matching this path (a relative path from the root artifact directory).

Response Structure

Field Name Type Description
root_uri STRING Root artifact directory for the run.
files An array of FileInfo File location and metadata for artifacts.

Update Run

Endpoint HTTP Method
2.0/mlflow/runs/update POST

Update run metadata.

Request Structure

Field Name Type Description
run_id STRING ID of the run to update. Must be provided.
run_uuid STRING [Deprecated, use run_id instead] ID of the run to update.. This field will be removed in a future MLflow version.
status RunStatus Updated status of the run.
end_time INT64 Unix timestamp in milliseconds of when the run ended.

Response Structure

Field Name Type Description
run_info RunInfo Updated metadata of the run.

Data Structures

Experiment

Experiment

Field Name Type Description
experiment_id STRING Unique identifier for the experiment.
name STRING Human readable name that identifies the experiment.
artifact_location STRING Location where artifacts for the experiment are stored.
lifecycle_stage STRING Current life cycle stage of the experiment: “active” or “deleted”. Deleted experiments are not returned by APIs.
last_update_time INT64 Last update time
creation_time INT64 Creation time

FileInfo

Metadata of a single artifact file or directory.

Field Name Type Description
path STRING Path relative to the root artifact directory run.
is_dir BOOL Whether the path is a directory.
file_size INT64 Size in bytes. Unset for directories.

Metric

Metric associated with a run, represented as a key-value pair.

Field Name Type Description
key STRING Key identifying this metric.
value DOUBLE Value associated with this metric.
timestamp INT64 The timestamp at which this metric was recorded.
step INT64 Step at which to log the metric.

Param

Param associated with a run.

Field Name Type Description
key STRING Key identifying this param.
value STRING Value associated with this param.

Run

A single run.

Field Name Type Description
info RunInfo Run metadata.
data RunData Run data.

RunData

Run data (metrics, params, and tags).

Field Name Type Description
metrics An array of Metric Run metrics.
params An array of Param Run parameters.
tags An array of RunTag Additional metadata key-value pairs.

RunInfo

Metadata of a single run.

Field Name Type Description
run_id STRING Unique identifier for the run.
run_uuid STRING [Deprecated, use run_id instead] Unique identifier for the run. This field will be removed in a future MLflow version.
experiment_id STRING The experiment ID.
user_id STRING User who initiated the run. This field is deprecated as of MLflow 1.0, and will be removed in a future MLflow release. Use ‘mlflow.user’ tag instead.
status RunStatus Current status of the run.
start_time INT64 Unix timestamp of when the run started in milliseconds.
end_time INT64 Unix timestamp of when the run ended in milliseconds.
artifact_uri STRING URI of the directory where artifacts should be uploaded. This can be a local path (starting with “/”), or a distributed file system (DFS) path, like s3://bucket/directory or dbfs:/my/directory. If not set, the local ./mlruns directory is chosen.
lifecycle_stage STRING Current life cycle stage of the experiment : OneOf(“active”, “deleted”)

RunTag

Tag for a run.

Field Name Type Description
key STRING The tag key.
value STRING The tag value.

RunStatus

Status of a run.

Name Description
RUNNING Run has been initiated.
SCHEDULED Run is scheduled to run at a later time.
FINISHED Run has completed.
FAILED Run execution failed.
KILLED Run killed by user.

ViewType

View type for ListExperiments query.

Name Description
ACTIVE_ONLY Default. Return only active experiments.
DELETED_ONLY Return only deleted experiments.
ALL Get all experiments.