Service Speed#

What kind of speeds can be expected from the Property Web Service?#

The Property Web Service can process hundreds of thousands of records per hour. The exact throughput the service achieves varies due to many factors, so your actual results will differ.

Some major factors impacting speed include:

  1. The number of threads used for sending requests:

    • The service will handle multiple requests from your application simultaneously, increasing overall throughput. We generally recommend up to 10 threads.

  2. Batching vs single-record requests:

    • The service can process 100 records in a batch (POST request) faster than 100 single-record GET requests.

  3. The type of input provided to the service:

    • Free-form addresses will process more slowly than parsed inputs (Address Lines, City + State or Postal).

    • Melissa Address Key (MAK) inputs will process relatively quickly since the MAK is a globally unique identifier.

  4. The quality of the input data provided to the service:

    • If data is poor or malformed, Melissa will attempt to correct it. This will reduce the processing speed.

  5. The number of output columns selected:

    • Requesting more response columns means more time querying our databases and larger payloads. More columns requested will result in slower responses.

With these variations in mind, you can expect the following approximate throughput rates:


Throughput (records / hour)


300,000 - 1,250,000


250,000 - 500,000


250,000 - 500,000

Data Accuracy#

Why does your service report some fields incorrectly? I know that those fields should have different values.#

The nature of property data means that we rely on 3,000+ counties in the US to update their data and provide it to us. While we update our database weekly with any updates provided to us, we are beholden to the schedule of each individual office and cannot perform the updates before they provide this data.

In addition, not every office will report this accurately, and we may inherit the errors within the web service.

Data Append Rates#

How often can we expect certain fields to be populated (what is the append rate)?#

While we have some general statistics for append rates, certain property attributes are filled out more accurately and consistently than others. Append rates can vary greatly by county. These rates are available by request.

Data Update Frequency#

How often is the data updated?#

The data is updated weekly with whatever updates we receive, but the frequency of new data can vary greatly depending on:

  • If the individual counties update their data and provide it

  • If there are any quality issues identified with the updates from the county

Generally speaking, tax assessments may occur as frequently as twice-annually, or they may not even have a specific interval. Many counties only perform tax assessments when properties are sold, when there is a significant reduction in property value, or improvements are made (if reported by the owner) to the property.

Estimated Value#

How are the EstimatedValue fields calculated?#

Our EstimatedValue fields are based on an algorithm that correlates multiple accepted AVM models to create a statistically accurate AVM value.

This statistical model accounts for items such as:

  • Property Types (residential, commercial, vacant land, etc)

  • Property Characteristics (square footage, number of bedrooms and bathrooms, lot size, property age, etc)

  • Historical data and trends

  • Public records and tax/assessment data

  • Comparables (properties with similar attributes in neighboring areas)

The Tax fields are the latest values from the county assessor’s office (tax assessments).

  • Values from tax assessments can be quite a bit lower than the EstimatedValue.

  • EstimatedValue should be used in most cases, unless there is a specific requirement to get the assessed value from the county.