Frankfurter · API Governance Rules

Frankfurter API Rules

Spectral linting rules defining API design standards and conventions for Frankfurter.

40 Rules error 14 warn 20 info 6
View Rules File View on GitHub

Rule Categories

examples info no only openapi operation parameter paths query response schema servers tags

Rules

error
info-title-frankfurter
API title must start with "Frankfurter".
$.info.title
error
info-description-required
Info description is required and must be meaningful.
$.info
error
info-version-required
API version must be defined.
$.info
warn
info-license-mit
License must be defined and is expected to be MIT.
$.info.license
warn
info-contact-required
Contact url must be defined.
$.info.contact
error
openapi-version-3-1
OpenAPI version must be 3.1.x.
$
error
servers-defined
At least one server must be defined.
$
error
servers-https-only
Server URLs must use HTTPS.
$.servers[*].url
info
servers-frankfurter-host
Server URLs should target the api.frankfurter.dev host (or self-host equivalent).
$.servers[*].url
warn
servers-versioned
Server URL should include a /v1 or /v2 version segment.
$.servers[*].url
error
paths-no-trailing-slash
Paths must not end with a trailing slash.
$.paths
error
paths-no-query-string
Paths must not contain query strings.
$.paths
warn
paths-kebab-or-template
Path segments should be kebab-case or templated parameters.
$.paths
error
operation-summary-required
Every operation must have a summary.
$.paths[*][get,post,put,patch,delete]
warn
operation-description-required
Every operation must have a description.
$.paths[*][get,post,put,patch,delete]
warn
operation-summary-frankfurter-prefix
Operation summaries should start with "Frankfurter".
$.paths[*][get,post,put,patch,delete].summary
warn
operation-id-camel-case
operationId must be camelCase when present (v2 convention).
$.paths[*][get,post,put,patch,delete].operationId
warn
operation-tags-required
Every operation must declare at least one tag.
$.paths[*][get,post,put,patch,delete]
info
operation-microcks-extension
Operation should declare an x-microcks-operation block for mock-server compatibility.
$.paths[*][get,post,put,patch,delete]
warn
tags-global-defined
Top-level tags array must be defined and non-empty.
$
info
tags-have-description
Each global tag should declare a description.
$.tags[*]
warn
parameter-description-required
Every parameter must have a description.
$.paths[*][*].parameters[*]
warn
parameter-snake-case
Parameter names should be snake_case (matches Frankfurter convention — base, quotes, from, to, start_date, end_date, providers).
$.paths[*][*].parameters[*].name
error
parameter-schema-required
Every parameter must declare a schema with a type.
$.paths[*][*].parameters[*]
error
no-request-bodies
Frankfurter API operations must not declare a requestBody (the API is read-only over GET).
$.paths[*][get,delete]
error
response-200-required
Every GET operation must define a 200 response.
$.paths[*].get.responses
warn
response-404-defined
GET operations should declare a 404 response for missing data.
$.paths[*].get.responses
warn
response-content-json
2xx responses should use application/json (or application/x-ndjson for streaming).
$.paths[*][*].responses[?(@property.match(/^2/))].content
error
response-description-required
Every response must have a description.
$.paths[*][*].responses[*]
warn
schema-property-snake-case
Schema property names should be snake_case (matches API JSON output — iso_code, iso_numeric, start_date, end_date, pivot_currency, etc.).
$.components.schemas[*].properties
info
schema-property-description
Top-level schema properties should have descriptions.
$.components.schemas[*].properties[*]
warn
schema-type-defined
Component schemas must declare a type (or use composition keywords).
$.components.schemas[*]
warn
no-security-schemes
Frankfurter is a public open API — no security schemes should be declared.
$.components.securitySchemes
warn
no-global-security
Frankfurter operations should not require security.
$
error
only-get-methods
Frankfurter exposes only GET endpoints — no write methods are permitted.
$.paths[*]
warn
no-empty-descriptions
Descriptions must not be empty.
$..description
info
examples-encouraged
Schemas should provide examples to aid documentation and mock generation.
$.components.schemas[*]
warn
servers-expected-domain
Server URLs should be on the frankfurter.dev domain.
$.servers[*].url
warn
query-params-casing
Query parameters should be snake_case (the dominant convention in this API).
$.paths[*][get,post,put,patch,delete].parameters[?(@.in=='query')]
info
schema-names-casing
Component schema names should be snake_case (the dominant convention in this API).
$.components.schemas

Spectral Ruleset

Raw ↑ 
# frankfurter — Spectral ruleset (strengthened)
# Plain Spectral. Existing hand-authored rules preserved; measured rules added
# from this provider's own OpenAPI conventions by strengthen_ruleset.py,
# then self-validated against the spec.
#
# Provenance:
#   - servers-https-only: 100% of servers already https (error)
#   - servers-expected-domain: 2/2 servers on frankfurter.dev
#   - path-params-casing: snake @ 100% (n=7)
#   - query-params-casing: snake @ 100% (n=20)
#   - operationid-casing: camel @ 100% (n=5)
#   - schema-names-casing: snake @ 42% (n=12)
#   - schema-properties-casing: snake @ 100% (n=32)
#   - merge: kept 37 existing, added 3 measured, upgraded 0
#   - added: servers-expected-domain, query-params-casing, schema-names-casing
extends:
  - spectral:oas
rules:
  info-title-frankfurter:
    description: API title must start with "Frankfurter".
    message: '{{property}} should start with "Frankfurter"'
    severity: error
    given: $.info.title
    then:
      function: pattern
      functionOptions:
        match: ^Frankfurter\b
  info-description-required:
    description: Info description is required and must be meaningful.
    severity: error
    given: $.info
    then:
    - field: description
      function: truthy
    - field: description
      function: length
      functionOptions:
        min: 40
  info-version-required:
    description: API version must be defined.
    severity: error
    given: $.info
    then:
      field: version
      function: truthy
  info-license-mit:
    description: License must be defined and is expected to be MIT.
    severity: warn
    given: $.info.license
    then:
    - field: name
      function: truthy
    - field: name
      function: pattern
      functionOptions:
        match: ^MIT
  info-contact-required:
    description: Contact url must be defined.
    severity: warn
    given: $.info.contact
    then:
      field: url
      function: truthy
  openapi-version-3-1:
    description: OpenAPI version must be 3.1.x.
    severity: error
    given: $
    then:
      field: openapi
      function: pattern
      functionOptions:
        match: ^3\.1\.
  servers-defined:
    description: At least one server must be defined.
    severity: error
    given: $
    then:
      field: servers
      function: truthy
  servers-https-only:
    description: Server URLs must use HTTPS.
    severity: error
    given: $.servers[*].url
    then:
      function: pattern
      functionOptions:
        match: ^https://
  servers-frankfurter-host:
    description: Server URLs should target the api.frankfurter.dev host (or self-host equivalent).
    severity: info
    given: $.servers[*].url
    then:
      function: pattern
      functionOptions:
        match: frankfurter
  servers-versioned:
    description: Server URL should include a /v1 or /v2 version segment.
    severity: warn
    given: $.servers[*].url
    then:
      function: pattern
      functionOptions:
        match: /v[12](/|$)
  paths-no-trailing-slash:
    description: Paths must not end with a trailing slash.
    severity: error
    given: $.paths
    then:
      field: '@key'
      function: pattern
      functionOptions:
        notMatch: /$
  paths-no-query-string:
    description: Paths must not contain query strings.
    severity: error
    given: $.paths
    then:
      field: '@key'
      function: pattern
      functionOptions:
        notMatch: \?
  paths-kebab-or-template:
    description: Path segments should be kebab-case or templated parameters.
    message: Path segment "{{error}}" should be kebab-case or a parameter template.
    severity: warn
    given: $.paths
    then:
      field: '@key'
      function: pattern
      functionOptions:
        match: ^(/[a-z0-9\-]+|/\{[A-Za-z_][A-Za-z0-9_]*\}|/\{[A-Za-z_][A-Za-z0-9_]*\}\.\.|/\{[A-Za-z_][A-Za-z0-9_]*\}\.\.\{[A-Za-z_][A-Za-z0-9_]*\})+$
  operation-summary-required:
    description: Every operation must have a summary.
    severity: error
    given: $.paths[*][get,post,put,patch,delete]
    then:
      field: summary
      function: truthy
  operation-description-required:
    description: Every operation must have a description.
    severity: warn
    given: $.paths[*][get,post,put,patch,delete]
    then:
      field: description
      function: truthy
  operation-summary-frankfurter-prefix:
    description: Operation summaries should start with "Frankfurter".
    severity: warn
    given: $.paths[*][get,post,put,patch,delete].summary
    then:
      function: pattern
      functionOptions:
        match: ^Frankfurter\b
  operation-id-camel-case:
    description: operationId must be camelCase when present (v2 convention).
    severity: warn
    given: $.paths[*][get,post,put,patch,delete].operationId
    then:
      function: pattern
      functionOptions:
        match: ^[a-z][a-zA-Z0-9]+$
  operation-tags-required:
    description: Every operation must declare at least one tag.
    severity: warn
    given: $.paths[*][get,post,put,patch,delete]
    then:
      field: tags
      function: truthy
  operation-microcks-extension:
    description: Operation should declare an x-microcks-operation block for mock-server compatibility.
    severity: info
    given: $.paths[*][get,post,put,patch,delete]
    then:
      field: x-microcks-operation
      function: truthy
  tags-global-defined:
    description: Top-level tags array must be defined and non-empty.
    severity: warn
    given: $
    then:
      field: tags
      function: truthy
  tags-have-description:
    description: Each global tag should declare a description.
    severity: info
    given: $.tags[*]
    then:
      field: description
      function: truthy
  parameter-description-required:
    description: Every parameter must have a description.
    severity: warn
    given: $.paths[*][*].parameters[*]
    then:
      field: description
      function: truthy
  parameter-snake-case:
    description: Parameter names should be snake_case (matches Frankfurter convention — base, quotes,
      from, to, start_date, end_date, providers).
    severity: warn
    given: $.paths[*][*].parameters[*].name
    then:
      function: pattern
      functionOptions:
        match: ^[a-z][a-z0-9_]*$
  parameter-schema-required:
    description: Every parameter must declare a schema with a type.
    severity: error
    given: $.paths[*][*].parameters[*]
    then:
      field: schema
      function: truthy
  no-request-bodies:
    description: Frankfurter API operations must not declare a requestBody (the API is read-only over
      GET).
    severity: error
    given: $.paths[*][get,delete]
    then:
      field: requestBody
      function: falsy
  response-200-required:
    description: Every GET operation must define a 200 response.
    severity: error
    given: $.paths[*].get.responses
    then:
      field: '200'
      function: truthy
  response-404-defined:
    description: GET operations should declare a 404 response for missing data.
    severity: warn
    given: $.paths[*].get.responses
    then:
      field: '404'
      function: truthy
  response-content-json:
    description: 2xx responses should use application/json (or application/x-ndjson for streaming).
    severity: warn
    given: $.paths[*][*].responses[?(@property.match(/^2/))].content
    then:
      function: schema
      functionOptions:
        schema:
          oneOf:
          - required:
            - application/json
          - required:
            - application/x-ndjson
          - required:
            - application/json
            - application/x-ndjson
  response-description-required:
    description: Every response must have a description.
    severity: error
    given: $.paths[*][*].responses[*]
    then:
      field: description
      function: truthy
  schema-property-snake-case:
    description: Schema property names should be snake_case (matches API JSON output — iso_code, iso_numeric,
      start_date, end_date, pivot_currency, etc.).
    severity: warn
    given: $.components.schemas[*].properties
    then:
      field: '@key'
      function: pattern
      functionOptions:
        match: ^[a-z][a-z0-9_]*$
  schema-property-description:
    description: Top-level schema properties should have descriptions.
    severity: info
    given: $.components.schemas[*].properties[*]
    then:
      field: description
      function: truthy
  schema-type-defined:
    description: Component schemas must declare a type (or use composition keywords).
    severity: warn
    given: $.components.schemas[*]
    then:
      function: schema
      functionOptions:
        schema:
          anyOf:
          - required:
            - type
          - required:
            - allOf
          - required:
            - oneOf
          - required:
            - anyOf
          - required:
            - $ref
  no-security-schemes:
    description: Frankfurter is a public open API — no security schemes should be declared.
    severity: warn
    given: $.components.securitySchemes
    then:
      function: falsy
  no-global-security:
    description: Frankfurter operations should not require security.
    severity: warn
    given: $
    then:
      field: security
      function: falsy
  only-get-methods:
    description: Frankfurter exposes only GET endpoints — no write methods are permitted.
    severity: error
    given: $.paths[*]
    then:
      function: schema
      functionOptions:
        schema:
          not:
            anyOf:
            - required:
              - post
            - required:
              - put
            - required:
              - patch
            - required:
              - delete
  no-empty-descriptions:
    description: Descriptions must not be empty.
    severity: warn
    given: $..description
    then:
      function: length
      functionOptions:
        min: 1
  examples-encouraged:
    description: Schemas should provide examples to aid documentation and mock generation.
    severity: info
    given: $.components.schemas[*]
    then:
      field: example
      function: truthy
  servers-expected-domain:
    description: Server URLs should be on the frankfurter.dev domain.
    severity: warn
    given: $.servers[*].url
    then:
      function: pattern
      functionOptions:
        match: frankfurter\.dev
  query-params-casing:
    description: Query parameters should be snake_case (the dominant convention in this API).
    severity: warn
    given: $.paths[*][get,post,put,patch,delete].parameters[?(@.in=='query')]
    then:
      field: name
      function: casing
      functionOptions:
        type: snake
  schema-names-casing:
    description: Component schema names should be snake_case (the dominant convention in this API).
    severity: info
    given: $.components.schemas
    then:
      field: '@key'
      function: casing
      functionOptions:
        type: snake