Data Formats
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MUST Use JSON to Encode Structured DataWe use a minimal JSON representation to output objects from the API. This may in the future be extended to use JSON:API if the functionality it offers is beneficial, however we are taking the approach of starting simple and extending if necessary. This could be done in a backwards compatible way by representing the same objects in a JSON:API structure as well as the simple JSON structure.
The structure we currently use is:
A single object A simple collection of attributes and their values. The attributes should be camel-cased.
A collection of objects This should have a root element matching the pluralised name of the object:
An error object We use the status code to represent the success or failure of a request. We also pass back an object with more information about the error:
^[a-z][A-Z0-9]*$
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MUST use camelCase property names: Property names are restricted to ASCII strings. The first character must be a letter, or an underscore, and subsequent characters can be a letter, or a number.
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MUST pluralise array namesTo indicate they contain multiple values we prefer to pluralise array names. This implies that object names should in turn be singular.
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MUST Boolean property values must not be nullSchema based JSON properties that are by design booleans must not be presented as nulls. A boolean is essentially a closed enumeration of two values, true and false. If the content has a meaningful null value, strongly prefer to replace the boolean with enumeration of named values or statuses - for example acceptedTermsAndConditions with true or false can be replaced with termsAndConditions with values yes, no and unknown.
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SHOULD Null values should have their fields removedOpenAPI, which is in common use, doesn’t support null field values (it does allow omitting that field completely if it is not marked as required). However that doesn’t prevent clients and servers sending and receiving those fields with null values. Also, in some cases null may be a meaningful value - for example, JSON Merge Patch RFC 7382) using null to indicate property deletion.
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MUST not use null values for empty arrayEmpty array values can unambiguously be represented as the empty list,[]
.
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MAY Use non-JSON Media Types for Binary Data or Alternative Content RepresentationsOther media types may be used in following cases:
Transferring binary data or data whose structure is not relevant. This is the case if payload structure is not interpreted and consumed by clients as is. Example of such use case is downloading images in formats JPG, PNG, GIF.
In addition to JSON version alternative data representations (e.g. in formats PDF, DOC, XML) may be made available through content negotiation.
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MUST Use Standard Date and Time Formats#
JSON PayloadRepresent date and time format as RFC 3339.
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HTTP headersHTTP headers including the proprietary headers use the HTTP date format defined in RFC 7231.
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MAY Use Standards for Country, Language and Currency CodesUse the following standard formats for country, language and currency codes:
ISO 3166-1-alpha2 country codes
- (It is "GB", not "UK", even though "UK" has seen some use at Zalando)
- BCP-47 (based on ISO 639-1) for language variants
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MUST Define Format for Type Number and IntegerWhenever an API defines a property of type number
or integer
, the precision must be defined by the format as follows to prevent clients from guessing the precision incorrectly, and thereby changing the value unintentionally:
type | format | specified value range |
---|---|---|
integer | int32 | integer between -2^31 and 2^31-1 |
integer | int64 | integer between -2^63 and 2^63-1 |
integer | bigint | arbitrarily large signed integer number |
number | float | IEEE 754-2008/ISO 60559:2011 binary64 decimal number |
number | double | IEEE 754-2008/ISO 60559:2011 binary128 decimal number |
number | decimal | arbitrarily precise signed decimal number |
The precision must be translated by clients and servers into the most specific language types. E.g. for the following definitions the most specific language types in Java will translate to BigDecimal
for Money.amount
and int
or Integer
for the OrderList.page_size
:
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SHOULD Date property values should conform to RFC 3339Use the date and time formats defined by RFC 3339:
for "date" use strings matching
date-fullyear "-" date-month "-" date-mday
, for example:2015-05-28
for "date-time" use strings matching
full-date "T" full-time
, for example2015-05-28T14:07:17Z
Note that the OpenAPI format
"date-time" corresponds to "date-time" in the RFC) and 2015-05-28
for a date (note that the OpenAPI format "date" corresponds to "full-date" in the RFC). Both are specific profiles, a subset of the international standard ISO 8601.
A zone offset may be used (both, in request and responses) — this is simply defined by the standards. However, we encourage restricting dates to UTC and without offsets. For example 2015-05-28T14:07:17Z
rather than 2015-05-28T14:07:17+00:00
. From experience we have learned that zone offsets are not easy to understand and often not correctly handled. Note also that zone offsets are different from local times that might be including daylight saving time. Localization of dates should be done by the services that provide user interfaces, if required.
When it comes to storage, all dates should be consistently stored in UTC without a zone offset. Localization should be done locally by the services that provide user interfaces, if required.
Sometimes it can seem data is naturally represented using numerical timestamps, but this can introduce interpretation issues with precision
- for example whether to represent a timestamp as 1460062925, 1460062925000 or 1460062925.000. Date strings, though more verbose and requiring more effort to parse, avoid this ambiguity.
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SHOULD Time durations and intervals could conform to ISO 8601Schema based JSON properties that are by design durations and intervals could be strings formatted as recommended by ISO 8601 (Appendix A of RFC 3339 contains a grammar for durations).
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SHOULD Use standards for Language, Country and CurrencyBCP-47 (based on ISO 639-1) for language variants