RFC 9457
Problem Details for HTTP APIs
Problem Details for HTTP APIs
Abstract
This document defines a "problem detail" to carry machine-readable details of errors in HTTP response content to avoid the need to define new error response formats for HTTP APIs.
This document obsoletes RFC 7807.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9457 .
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info ) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.
Table of Contents
- 1. Introduction
- 2. Requirements Language
- 3. The Problem Details JSON Object
- 4. Defining New Problem Types
- 5. Security Considerations
- 6. IANA Considerations
- 7. References
- Appendix A. JSON Schema for HTTP Problems
- Appendix B. HTTP Problems and XML
- Appendix C. Using Problem Details with Other Formats
- Appendix D. Changes from RFC 7807
- Acknowledgements
- Authors' Addresses
1. Introduction
HTTP status codes (Section 15 of [HTTP]) cannot always convey enough information about errors to be helpful. While humans using web browsers can often understand an HTML [HTML5] response content, non-human consumers of HTTP APIs have difficulty doing so.
To address that shortcoming, this specification defines simple JSON [JSON] and XML [XML] document formats to describe the specifics of a problem encountered -- "problem details".
For example, consider a response indicating that the client's account doesn't have enough credit. The API's designer might decide to use the 403 Forbidden status code to inform generic HTTP software (such as client libraries, caches, and proxies) of the response's general semantics. API-specific problem details (such as why the server refused the request and the applicable account balance) can be carried in the response content so that the client can act upon them appropriately (for example, triggering a transfer of more credit into the account).
This specification identifies the specific "problem type" (e.g., "out of credit") with a URI [URI]. HTTP APIs can use URIs under their control to identify problems specific to them or can reuse existing ones to facilitate interoperability and leverage common semantics (see Section 4.2).
Problem details can contain other information, such as a URI identifying the problem's specific occurrence (effectively giving an identifier to the concept "The time Joe didn't have enough credit last Thursday"), which can be useful for support or forensic purposes.
The data model for problem details is a JSON [JSON] object; when serialized as a JSON document, it uses the "application/problem+json" media type. Appendix B defines an equivalent XML format, which uses the "application/problem+xml" media type.
When they are conveyed in an HTTP response, the contents of problem details can be negotiated using proactive negotiation; see Section 12.1 of [HTTP]. In particular, the language used for human-readable strings (such as those in title and description) can be negotiated using the Accept-Language request header field (Section 12.5.4 of [HTTP]), although that negotiation may still result in a non-preferred, default representation being returned.
Problem details can be used with any HTTP status code, but they most naturally fit the semantics of 4xx and 5xx responses. Note that problem details are (naturally) not the only way to convey the details of a problem in HTTP. If the response is still a representation of a resource, for example, it's often preferable to describe the relevant details in that application's format. Likewise, defined HTTP status codes cover many situations with no need to convey extra detail.
This specification's aim is to define common error formats for applications that need one so that they aren't required to define their own or, worse, tempted to redefine the semantics of existing HTTP status codes. Even if an application chooses not to use it to convey errors, reviewing its design can help guide the design decisions faced when conveying errors in an existing format.
See Appendix D for a list of changes from [RFC 7807].
3. The Problem Details JSON Object
The canonical model for problem details is a JSON [JSON] object. When serialized in a JSON document, that format is identified with the "application/problem+json" media type.
For example:
Here, the out-of-credit problem (identified by its type) indicates the reason for the 403 in "title", identifies the specific problem occurrence with "instance", gives occurrence-specific details in "detail", and adds two extensions: "balance" conveys the account's balance, and "accounts" lists links where the account can be topped up.
When designed to accommodate it, problem-specific extensions can convey more than one instance of the same problem type. For example:
The fictional problem type here defines the "errors" extension, an array that describes the details of each validation error. Each member is an object containing "detail" to describe the issue and "pointer" to locate the problem within the request's content using a JSON Pointer [JSON-POINTER].
When an API encounters multiple problems that do not share the same type, it is RECOMMENDED that the most relevant or urgent problem be represented in the response. While it is possible to create generic "batch" problem types that convey multiple, disparate types, they do not map well into HTTP semantics.
Note also that the API has responded with the "application/problem+json" type, even though the client did not list it in Accept, as is allowed by HTTP (see Section 12.5.1 of [HTTP]).
POST /purchase HTTP/1.1
Host: store.example.com
Content-Type: application/json
Accept: application/json, application/problem+json
{
"item": 123456,
"quantity": 2
}
HTTP/1.1 403 Forbidden
Content-Type: application/problem+json
Content-Language: en
{
"type": "https://example.com/probs/out-of-credit",
"title": "You do not have enough credit.",
"detail": "Your current balance is 30, but that costs 50.",
"instance": "/account/12345/msgs/abc",
"balance": 30,
"accounts": ["/account/12345",
"/account/67890"]
}
POST /details HTTP/1.1
Host: account.example.com
Accept: application/json
{
"age": 42.3,
"profile": {
"color": "yellow"
}
}
HTTP/1.1 422 Unprocessable Content
Content-Type: application/problem+json
Content-Language: en
{
"type": "https://example.net/validation-error",
"title": "Your request is not valid.",
"errors": [
{
"detail": "must be a positive integer",
"pointer": "#/age"
},
{
"detail": "must be 'green', 'red' or 'blue'",
"pointer": "#/profile/color"
}
]
}
3.1. Members of a Problem Details Object
Problem detail objects can have the following members. If a member's value type does not match the specified type, the member MUST be ignored -- i.e., processing will continue as if the member had not been present.
3.1.1. "type"
The "type" member is a JSON string containing a URI reference [URI] that identifies the problem type. Consumers MUST use the "type" URI (after resolution, if necessary) as the problem type's primary identifier.
When this member is not present, its value is assumed to be "about:blank".
If the type URI is a locator (e.g., those with an "http" or "https" scheme), dereferencing it SHOULD provide human-readable documentation for the problem type (e.g., using HTML [HTML5]). However, consumers SHOULD NOT automatically dereference the type URI, unless they do so when providing information to developers (e.g., when a debugging tool is in use).
When "type" contains a relative URI, it is resolved relative to the document's base URI, as per [URI], Section 5. However, using relative URIs can cause confusion, and they might not be handled correctly by all implementations.
For example, if the two resources "https://api.example.org/foo/bar/123" and "https://api.example.org/widget/456" both respond with a "type" equal to the relative URI reference "example-problem", when resolved they will identify different resources ("https://api.example.org/foo/bar/example-problem" and "https://api.example.org/widget/example-problem", respectively). As a result, it is RECOMMENDED that absolute URIs be used in "type" when possible and that when relative URIs are used, they include the full path (e.g., "/types/123").
The type URI is allowed to be a non-resolvable URI. For example, the tag URI scheme [TAG] can be used to uniquely identify problem types:
However, resolvable type URIs are encouraged by this specification because it might become desirable to resolve the URI in the future. For example, if an API designer used the URI above and later adopted a tool that resolves type URIs to discover information about the error, taking advantage of that capability would require switching to a resolvable URI, creating a new identity for the problem type and thus introducing a breaking change.
tag:example@example.org,2021-09-17:OutOfLuck
3.1.2. "status"
The "status" member is a JSON number indicating the HTTP status code ([HTTP], Section 15) generated by the origin server for this occurrence of the problem.
The "status" member, if present, is only advisory; it conveys the HTTP status code used for the convenience of the consumer. Generators MUST use the same status code in the actual HTTP response, to assure that generic HTTP software that does not understand this format still behaves correctly. See Section 5 for further caveats regarding its use.
Consumers can use the status member to determine what the original status code used by the generator was when it has been changed (e.g., by an intermediary or cache) and when a message's content is persisted without HTTP information. Generic HTTP software will still use the HTTP status code.
3.1.3. "title"
The "title" member is a JSON string containing a short, human-readable summary of the problem type.
It SHOULD NOT change from occurrence to occurrence of the problem, except for localization (e.g., using proactive content negotiation; see [HTTP], Section 12.1).
The "title" string is advisory and is included only for users who are unaware of and cannot discover the semantics of the type URI (e.g., during offline log analysis).
3.1.4. "detail"
The "detail" member is a JSON string containing a human-readable explanation specific to this occurrence of the problem.
The "detail" string, if present, ought to focus on helping the client correct the problem, rather than giving debugging information.
Consumers SHOULD NOT parse the "detail" member for information; extensions are more suitable and less error-prone ways to obtain such information.
3.1.5. "instance"
The "instance" member is a JSON string containing a URI reference that identifies the specific occurrence of the problem.
When the "instance" URI is dereferenceable, the problem details object can be fetched from it. It might also return information about the problem occurrence in other formats through use of proactive content negotiation (see [HTTP], Section 12.5.1).
When the "instance" URI is not dereferenceable, it serves as a unique identifier for the problem occurrence that may be of significance to the server but is opaque to the client.
When "instance" contains a relative URI, it is resolved relative to the document's base URI, as per [URI], Section 5. However, using relative URIs can cause confusion, and they might not be handled correctly by all implementations.
For example, if the two resources "https://api.example.org/foo/bar/123" and "https://api.example.org/widget/456" both respond with an "instance" equal to the relative URI reference "example-instance", when resolved they will identify different resources ("https://api.example.org/foo/bar/example-instance" and "https://api.example.org/widget/example-instance", respectively). As a result, it is RECOMMENDED that absolute URIs be used in "instance" when possible, and that when relative URIs are used, they include the full path (e.g., "/instances/123").
3.2. Extension Members
Problem type definitions MAY extend the problem details object with additional members that are specific to that problem type.
For example, our out-of-credit problem above defines two such extensions -- "balance" and "accounts" to convey additional, problem-specific information.
Similarly, the "validation error" example defines an "errors" extension that contains a list of individual error occurrences found, with details and a pointer to the location of each.
Clients consuming problem details MUST ignore any such extensions that they don't recognize; this allows problem types to evolve and include additional information in the future.
When creating extensions, problem type authors should choose their names carefully. To be used in the XML format (see Appendix B), they will need to conform to the Name rule in [XML].
4. Defining New Problem Types
When an HTTP API needs to define a response that indicates an error condition, it might be appropriate to do so by defining a new problem type.
Before doing so, it's important to understand what they are good for and what is better left to other mechanisms.
Problem details are not a debugging tool for the underlying implementation; rather, they are a way to expose greater detail about the HTTP interface itself. Designers of new problem types need to carefully take into account the Section 5, in particular, the risk of exposing attack vectors by exposing implementation internals through error messages.
Likewise, truly generic problems -- i.e., conditions that might apply to any resource on the Web -- are usually better expressed as plain status codes. For example, a "write access disallowed" problem is probably unnecessary, since a 403 Forbidden status code in response to a PUT request is self-explanatory.
Finally, an application might have a more appropriate way to carry an error in a format that it already defines. Problem details are intended to avoid the necessity of establishing new "fault" or "error" document formats, not to replace existing domain-specific formats.
That said, it is possible to add support for problem details to existing HTTP APIs using HTTP content negotiation (e.g., using the Accept request header to indicate a preference for this format; see [HTTP], Section 12.5.1).
New problem type definitions MUST document:
- a type URI (typically, with the "http" or "https" scheme)
- a title that appropriately describes it (think short)
- the HTTP status code for it to be used with
4.1. Example
For example, if you are publishing an HTTP API to your online shopping cart, you might need to indicate that the user is out of credit (our example from above) and therefore cannot make the purchase.
If you already have an application-specific format that can accommodate this information, it's probably best to do that. However, if you don't, you might use one of the problem detail formats -- JSON if your API is JSON-based or XML if it uses that format.
To do so, you might look in the registry (Section 4.2) for an already-defined type URI that suits your purposes. If one is available, you can reuse that URI.
If one isn't available, you could mint and document a new type URI (which ought to be under your control and stable over time), an appropriate title and the HTTP status code that it will be used with, along with what it means and how it should be handled.
4.2. Registered Problem Types
This specification defines the "HTTP Problem Types" registry for common, widely used problem type URIs, to promote reuse.
The policy for this registry is Specification Required, per RFC 8126, Section 4.6.
When evaluating requests, the designated expert(s) should consider community feedback, how well-defined the problem type is, and this specification's requirements. Vendor-specific, application-specific, and deployment-specific values are unable to be registered. Specification documents should be published in a stable, freely available manner (ideally located with a URL) but need not be standards.
Registrations MAY use the prefix "https://iana.org/assignments/http-problem-types# " for the type URI. Note that those URIs may not be able to be resolved.
The following template should be used for registration requests:
iana.org/assignments/http-problem-types > for details on where to send registration requests.
- Type URI:
- [a URI for the problem type]
- Title:
- [a short description of the problem type]
- Recommended HTTP status code:
- [what status code is most appropriate to use with the type]
- Reference:
- [to a specification defining the type]
4.2.1. about:blank
This specification registers one Problem Type, "about:blank", as follows.
- Type URI:
- about:blank
- Title:
- See HTTP Status Code
- Recommended HTTP status code:
- N/A
- Reference:
- RFC 9457
5. Security Considerations
When defining a new problem type, the information included must be carefully vetted. Likewise, when actually generating a problem -- however it is serialized -- the details given must also be scrutinized.
Risks include leaking information that can be exploited to compromise the system, access to the system, or the privacy of users of the system.
Generators providing links to occurrence information are encouraged to avoid making implementation details such as a stack dump available through the HTTP interface, since this can expose sensitive details of the server implementation, its data, and so on.
The "status" member duplicates the information available in the HTTP status code itself, bringing the possibility of disagreement between the two. Their relative precedence is not clear, since a disagreement might indicate that (for example) an intermediary has changed the HTTP status code in transit (e.g., by a proxy or cache). Generic HTTP software (such as proxies, load balancers, firewalls, and virus scanners) are unlikely to know of or respect the status code conveyed in this member.
6. IANA Considerations
In the "application" registry under the "Media Types" registry, IANA has updated the "application/problem+json" and "application/problem+xml" registrations to refer to this document.
IANA has created the "HTTP Problem Types" registry as specified in Section 4.2 and populated it with "about:blank" as per Section 4.2.1.
7. References
7.1. Normative References
-
[ABNF]
-
D. Crocker, and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/ >.rfc5234 -
[HTTP]
-
R. Fielding, M. Nottingham, and J. Reschke, "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/ >.rfc9110 -
[JSON]
-
T. Bray, "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/ >.rfc8259 - [RFC2119]
-
S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/ >.rfc2119 - [RFC8126]
-
M. Cotton, B. Leiba, and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/ >.rfc8126 - [RFC8174]
-
B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/ >.rfc8174 -
[URI]
-
T. Berners-Lee, R. Fielding, and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/ >.rfc3986 - [XML]
-
T. Bray, J. Paoli, C. M. Sperberg-McQueen, E. Maler, and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", November 2008,
<https://www.w3.org/TR/ >.2008/ REC-xml-20081126/
7.2. Informative References
-
[ABOUT]
-
S. Moonesamy, "The "about" URI Scheme", RFC 6694, DOI 10.17487/RFC6694, August 2012,
<https://www.rfc-editor.org/info/ >.rfc6694 - [HTML5]
-
WHATWG, "HTML: Living Standard",
<https://html.spec.whatwg.org>. - [ISO-19757-2]
-
ISO, "Information technology -- Document Schema Definition Language (DSDL) -- Part 2: Regular-grammar-based validation -- RELAX NG", ISO/IEC 19757-2:2008, December 2008,
<https://www.iso.org/standard/ >.52348.html -
[JSON-POINTER]
-
P. Bryan, K. Zyp, and M. Nottingham, "JavaScript Object Notation (JSON) Pointer", RFC 6901, DOI 10.17487/RFC6901, April 2013,
<https://www.rfc-editor.org/info/ >.rfc6901 -
[JSON-SCHEMA]
-
Postman, A. Wright, H. Andrews, B. Hutton, and G. Dennis, "JSON Schema: A Media Type for Describing JSON Documents", Internet-Draft draft-bhutton-json-schema-01, June 2022,
<https://datatracker.ietf.org/doc/ >.html/ draft-bhutton-json-schema-01 - [RDFA]
-
, , , and , "RDFa Core 1.1 - Third Edition", March 2015,
<https://www.w3.org/TR/ >.2015/ REC-rdfa-core-20150317/ - [RFC7807]
-
M. Nottingham, and E. Wilde, "Problem Details for HTTP APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
<https://www.rfc-editor.org/info/ >.rfc7807 -
[TAG]
-
T. Kindberg, and S. Hawke, "The 'tag' URI Scheme", RFC 4151, DOI 10.17487/RFC4151, October 2005,
<https://www.rfc-editor.org/info/ >.rfc4151 -
[WEB-LINKING]
-
M. Nottingham, "Web Linking", RFC 8288, DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/ >.rfc8288 - [XSLT]
-
, , and , "Associating Style Sheets with XML documents 1.0 (Second Edition)", October 2010,
<https://www.w3.org/TR/ >.2010/ REC-xml-stylesheet-20101028/
Appendix A. JSON Schema for HTTP Problems
This section presents a non-normative JSON Schema [JSON-SCHEMA] for HTTP problem details. If there is any disagreement between it and the text of the specification, the latter prevails.
# NOTE: '\' line wrapping per RFC 8792
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"title": "An RFC 7807 problem object",
"type": "object",
"properties": {
"type": {
"type": "string",
"format": "uri-reference",
"description": "A URI reference that identifies the \
problem type."
},
"title": {
"type": "string",
"description": "A short, human-readable summary of the \
problem type."
},
"status": {
"type": "integer",
"description": "The HTTP status code \
generated by the origin server for this occurrence of the problem.",
"minimum": 100,
"maximum": 599
},
"detail": {
"type": "string",
"description": "A human-readable explanation specific to \
this occurrence of the problem."
},
"instance": {
"type": "string",
"format": "uri-reference",
"description": "A URI reference that identifies the \
specific occurrence of the problem. It may or may not yield \
further information if dereferenced."
}
}
}
Appendix B. HTTP Problems and XML
HTTP-based APIs that use XML [XML] can express problem details using the format defined in this appendix.
The RELAX NG schema [ISO-19757-2] for the XML format is:
Note that this schema is only intended as documentation and not as a normative schema that captures all constraints of the XML format. It is possible to use other XML schema languages to define a similar set of constraints (depending on the features of the chosen schema language).
The media type for this format is "application/problem+xml".
Extension arrays and objects are serialized into the XML format by considering an element containing a child or children to represent an object, except for elements containing only one or more child elements named "i", which are considered arrays. For example, the example above appears in XML as follows:
This format uses an XML namespace, primarily to allow embedding it into other XML-based formats; it does not imply that it can or should be extended with elements or attributes in other namespaces. The RELAX NG schema explicitly only allows elements from the one namespace used in the XML format. Any extension arrays and objects MUST be serialized into XML markup using only that namespace.
When using the XML format, it is possible to embed an XML processing instruction in the XML that instructs clients to transform the XML, using the referenced XSL Transformations (XSLT) code [XSLT]. If this code is transforming the XML into (X)HTML, then it is possible to serve the XML format, and yet have clients capable of performing the transformation display human-friendly (X)HTML that is rendered and displayed at the client. Note that when using this method, it is advisable to use XSLT 1.0 in order to maximize the number of clients capable of executing the XSLT code.
default namespace ns = "urn:ietf:rfc:7807"
start = problem
problem =
element problem {
( element type { xsd:anyURI }?
& element title { xsd:string }?
& element detail { xsd:string }?
& element status { xsd:positiveInteger }?
& element instance { xsd:anyURI }? ),
anyNsElement
}
anyNsElement =
( element ns:* { anyNsElement | text }
| attribute * { text })*
HTTP/1.1 403 Forbidden
Content-Type: application/problem+xml
Content-Language: en
<?xml version="1.0" encoding="UTF-8"?>
<problem xmlns="urn:ietf:rfc:7807">
<type>https://example.com/probs/out-of-credit</type>
<title>You do not have enough credit.</title>
<detail>Your current balance is 30, but that costs 50.</detail>
<instance>https://example.net/account/12345/msgs/abc</instance>
<balance>30</balance>
<accounts>
<i>https://example.net/account/12345</i>
<i>https://example.net/account/67890</i>
</accounts>
</problem>
Appendix C. Using Problem Details with Other Formats
In some situations, it can be advantageous to embed problem details in formats other than those described here. For example, an API that uses HTML [HTML5] might want to also use HTML for expressing its problem details.
Problem details can be embedded in other formats either by encapsulating one of the existing serializations (JSON or XML) into that format or by translating the model of a problem detail (as specified in Section 3) into the format's conventions.
For example, in HTML, a problem could be embedded by encapsulating JSON in a script tag:
or by defining a mapping into a Resource Description Framework in Attributes (RDFa) [RDFA].
This specification does not make specific recommendations regarding embedding problem details in other formats; the appropriate way to embed them depends both upon the format in use and application of that format.
<script type="application/problem+json">
{
"type": "https://example.com/probs/out-of-credit",
"title": "You do not have enough credit.",
"detail": "Your current balance is 30, but that costs 50.",
"instance": "/account/12345/msgs/abc",
"balance": 30,
"accounts": ["/account/12345",
"/account/67890"]
}
</script>
Appendix D. Changes from RFC 7807
This revision has made the following changes:
- Section 4.2 introduces a registry of common problem type URIs
- Section 3 clarifies how multiple problems should be treated
- Section 3.1.1 provides guidance for using type URIs that cannot be dereferenced
Acknowledgements
The authors would like to thank Jan Algermissen, Subbu Allamaraju, Mike Amundsen, Roy Fielding, Eran Hammer, Sam Johnston, Mike McCall, Julian Reschke, and James Snell for their comments and suggestions.
Authors' Addresses
Mark Nottingham
Email: mnot@mnot.net
Erik Wilde
Email: erik.wilde@dret.net
Sanjay Dalal
United States of America
