# Vendor facets — Fern. Two products: Fern Docs (hosted docs with llms.txt, Markdown, an
# RFC 9727 api-catalog, a served OpenAPI 3.1, provider-authored skills and an Ask-Fern MCP
# server) and Fern SDK generation (nine languages, plus an early-access CLI generator). It is the
# widest reach in this set: SDKs and a CLI move Developer Ergonomics points no docs-only platform
# can touch, and `fern api enrich` can write examples into the contract itself.
vendor: fern-api
name: Fern
website: https://buildwithfern.com
areas:
- documentation
- sdk-generation
registry_keys:
- fern
rubric_schema_version: 0.22.0
generated: '2026-09-25'
features_refreshed: '2026-09-25'
basis: measured
summary: >-
  Fern reaches further than any documentation-only vendor: generated SDKs published to the provider's
  own registries earn sdk_count_1 and sdk_count_3, the CLI generator earns cli_present, and `fern api
  enrich` merges AI-generated examples into the OpenAPI, the one route here into contract-side examples.
  The docs side adds llms.txt, an RFC 9727 api-catalog, a served OpenAPI 3.1 and a place to publish skills
  the provider writes. The qualifiers: the docs MCP server is one Ask-Fern template graded `platform`,
  SDKs and the CLI count only once published and declared, the CLI generator is early access, and the
  served contract only adds a contract for a provider whose source is not already OpenAPI.
features:
- id: sdk-generator
  name: SDK generation in nine languages
  description: >-
    Generates TypeScript, Python, Go, Java, C#, PHP, Ruby, Swift and Rust SDKs from OpenAPI or a Fern
    definition, and publishes them to npm, PyPI, Maven Central, NuGet and others.
  source: https://buildwithfern.com/learn/sdks/overview/capabilities
  tier: unknown
- id: sdk-idempotency
  name: SDK idempotency headers, retries and pagination
  description: >-
    Generated SDKs carry idempotency headers, retries with backoff, auto-pagination, OAuth token refresh
    and webhook signature verification.
  source: https://buildwithfern.com/learn/sdks/overview/capabilities
  tier: unknown
- id: cli-generator
  name: CLI generator
  description: >-
    Generates a single-binary CLI from an OpenAPI or GraphQL definition and publishes it to npm, Homebrew
    and GitHub Releases.
  source: https://buildwithfern.com/learn/cli-generator/get-started/overview
  tier: unknown
- id: hosted-docs
  name: Fern Docs hosted site and API reference
  description: A hosted docs site with guides and a generated API reference on the provider's domain.
  source: https://buildwithfern.com/learn/docs/getting-started/capabilities
  tier: unknown
- id: api-explorer
  name: API Explorer
  description: >-
    Authenticated real calls from the reference, prefilled from spec defaults, across all declared auth
    schemes.
  source: https://buildwithfern.com/learn/docs/api-references/api-explorer
  tier: unknown
- id: sdk-snippets
  name: SDK and HTTP snippets in the reference
  description: SDK and HTTP code examples generated from the request/response examples in the definition.
  source: https://buildwithfern.com/learn/docs/llms.txt
  tier: unknown
- id: ai-examples
  name: AI-generated examples and `fern api enrich`
  description: >-
    Generates realistic request/response examples for every endpoint; `fern api enrich` merges them into
    native OpenAPI example fields.
  source: https://buildwithfern.com/learn/docs/ai-features/ai-examples
  tier: unknown
- id: llms-txt
  name: Generated llms.txt at every level
  description: Maintains llms.txt at the root and per section, linking the served OpenAPI and AsyncAPI
    specs.
  source: https://buildwithfern.com/learn/docs/ai-features/llms-txt
  tier: unknown
- id: api-catalog
  name: RFC 9727 api-catalog
  description: >-
    Serves /.well-known/api-catalog generated from the visible API reference, advertised in a Link header;
    empty for authenticated sites.
  source: https://buildwithfern.com/learn/docs/ai-features/api-catalog
  tier: unknown
- id: served-openapi
  name: Served OpenAPI 3.1 (and AsyncAPI 2.6)
  description: >-
    Every docs site serves /openapi.json and /openapi.yaml generated from the same definition as the docs,
    including webhooks and security schemes.
  source: https://buildwithfern.com/learn/docs/developer-tools/openapi-spec
  tier: unknown
- id: custom-skills
  name: Provider-authored Agent Skills hosting
  description: >-
    Serves skills the provider places under fern/.well-known/agent-skills/ with a v0.2.0 index and an
    Install skills button.
  source: https://buildwithfern.com/learn/docs/ai-features/host-skills
  tier: unknown
- id: docs-mcp
  name: MCP server for the docs site
  description: >-
    A Fern-hosted MCP server at <docs>/_mcp/server with one Ask-Fern question-answering tool, on sites
    with Ask Fern enabled.
  source: https://buildwithfern.com/learn/docs/ai-features/mcp-server
  tier: unknown
- id: changelog
  name: Changelog pages with RSS
  description: A changelog folder renders dated, tag-filterable entries with an RSS feed.
  source: https://buildwithfern.com/learn/docs/configuration/changelogs
  tier: unknown
- id: postman-generator
  name: Fern-to-Postman generator (deprecated)
  description: >-
    The Postman collection generator is no longer maintained; Fern points users to Postman's OpenAPI import.
  source: https://buildwithfern.com/learn/docs/integrations/postman
  tier: unknown
- id: markdown-access
  name: Markdown pages and agent directives
  description: >-
    Every page as Markdown at <url>.md, with a configurable directive prepended to pages served to agents.
  source: https://buildwithfern.com/learn/llms.txt
  tier: unknown
maps:
- feature: sdk-generator
  check: sdk_count_1
  layer: composite
  provider_must: >-
    Publish at least one generated SDK to a public registry under its own name and declare it as an SDK
    pointer.
  catalog_pass_rate: 0.148
  facet: developer_ergonomics
  points: 3
  baseline_pass_rate: 0.413
  cohort_pct: 61.9
  control_pct: 41.2
  delta_pp: 20.7
- feature: sdk-generator
  check: sdk_count_3
  layer: composite
  provider_must: Publish three or more SDKs and declare each as an SDK pointer.
  catalog_pass_rate: 0.018
  facet: developer_ergonomics
  points: 4
  baseline_pass_rate: 0.043
  cohort_pct: 0.0
  control_pct: 4.3
  delta_pp: -4.3
- feature: cli-generator
  check: cli_present
  layer: composite
  provider_must: Get into the early-access programme, publish the CLI, and declare it as a CLI pointer.
  catalog_pass_rate: 0.063
  facet: developer_ergonomics
  points: 3
  baseline_pass_rate: 0.19
  cohort_pct: 23.8
  control_pct: 19.0
  delta_pp: 4.8
- feature: ai-examples
  check: examples_present
  layer: composite
  provider_must: >-
    Run `fern api enrich` and publish the enriched OpenAPI as its contract; examples shown only in the
    docs do not count.
  note: >-
    The examples are model-generated from the definition, not captured from real traffic; the check does
    not distinguish, and this file says so.
  catalog_pass_rate: 0.024
  facet: contract_quality
  points: 4
  baseline_pass_rate: 0.233
  cohort_pct: 6.8
  control_pct: 23.4
  delta_pp: -16.6
- feature: ai-examples
  check: openapi_examples
  layer: agent_readiness
  grade: verified
  provider_must: Publish the enriched contract; without it Fern reaches only the documented link tier.
  note: >-
    Enrichment covers every endpoint, so the share clears the verified tier; same model-generated caveat.
  points: 7
  baseline_pass_rate: 0.36
  cohort_pct: 16.7
  control_pct: 36.1
  delta_pp: -19.4
- feature: api-explorer
  check: console_or_sandbox
  layer: composite
  provider_must: Declare the explorer as a Console pointer.
  catalog_pass_rate: 0.089
  facet: developer_ergonomics
  points: 3
  baseline_pass_rate: 0.332
  cohort_pct: 42.9
  control_pct: 33.2
  delta_pp: 9.7
- feature: hosted-docs
  check: documentation_present
  layer: composite
  provider_must: Declare the site as a Documentation pointer.
  catalog_pass_rate: 0.453
  facet: developer_ergonomics
  points: 4
  baseline_pass_rate: 0.95
  saturated: true
  saturated_note: >-
    95% of providers with a contract, docs and a reference already earn this; the vendor cannot move it
    for most of its buyers.
  cohort_pct: 100.0
  control_pct: 95.0
  delta_pp: 5.0
- feature: hosted-docs
  check: api_reference_present
  layer: composite
  provider_must: Declare the reference as an APIReference pointer.
  catalog_pass_rate: 0.222
  facet: developer_ergonomics
  points: 3
  baseline_pass_rate: 0.942
  saturated: true
  saturated_note: >-
    94% of providers with a contract, docs and a reference already earn this; the vendor cannot move it
    for most of its buyers.
  cohort_pct: 95.2
  control_pct: 94.1
  delta_pp: 1.1
- feature: llms-txt
  check: llms_txt_published
  layer: composite
  provider_must: Serve the docs from its own domain.
  note: >-
    Generated from the provider's own docs on the provider's domain, so it reads as the provider's (rule
    2's own-content, own-domain case).
  catalog_pass_rate: 0.351
  facet: discoverability
  points: 4
  baseline_pass_rate: 0.65
  cohort_pct: 90.5
  control_pct: 64.9
  delta_pp: 25.6
- feature: api-catalog
  check: well_known_published
  layer: composite
  provider_must: >-
    Serve the docs at the root of a host the harvest probes (docs.<domain>) and keep the site public;
    under a basepath the catalog moves to <basepath>/.well-known/api-catalog, and an authenticated site
    returns an empty linkset.
  catalog_pass_rate: 0.005
  facet: discoverability
  points: 6
  baseline_pass_rate: 0.018
  cohort_pct: 9.5
  control_pct: 1.8
  delta_pp: 7.7
- feature: api-catalog
  check: well_known_catalog
  layer: agent_readiness
  provider_must: Declare the api-catalog URL as an APICatalog / WellKnown pointer.
  points: 4
  baseline_pass_rate: 0.061
  cohort_pct: 57.1
  control_pct: 5.9
  delta_pp: 51.2
- feature: custom-skills
  check: agent_skills
  layer: agent_readiness
  credit: 1.0
  provider_must: Write the skills; Fern serves only what the provider places under .well-known/agent-skills/.
  note: >-
    Provider-authored on the provider's domain, so first-party. Fern's own fern-docs skill teaches agents
    to edit Fern sites and earns the provider nothing.
  points: 5
  baseline_pass_rate: 0.236
  cohort_pct: 40.5
  control_pct: 23.5
  delta_pp: 17.0
- feature: custom-skills
  check: agent_skill_present
  layer: composite
  credit: 1.0
  provider_must: Declare the skills index as an AgentSkill pointer.
  note: Same artifact as agent_skills.
  catalog_pass_rate: 0.033
  facet: developer_ergonomics
  points: 3
  baseline_pass_rate: 0.236
  cohort_pct: 40.5
  control_pct: 23.5
  delta_pp: 17.0
- feature: docs-mcp
  check: mcp_server
  layer: agent_readiness
  grade: platform
  note: >-
    One Fern-hosted Ask-Fern template answering docs questions (2 AI credits per call); 0.22.0 grades
    that `platform` (0.25 of 12).
  points: 12
  baseline_pass_rate: 0.22
  cohort_pct: 54.3
  control_pct: 21.8
  delta_pp: 32.5
- feature: changelog
  check: change_log_present
  layer: composite
  provider_must: Keep the changelog folder current and declare it as a ChangeLog pointer.
  catalog_pass_rate: 0.157
  facet: operational_transparency
  points: 6
  baseline_pass_rate: 0.438
  cohort_pct: 52.4
  control_pct: 43.8
  delta_pp: 8.6
- feature: served-openapi
  check: contract_present
  layer: composite
  conditional: true
  condition: >-
    Only when the provider's source is a Fern definition, gRPC or OpenRPC and the served /openapi.json
    becomes its first published OpenAPI.
  creates_artifact: true
  note: For a provider that already publishes OpenAPI, the served copy is a duplicate and adds nothing.
  catalog_pass_rate: 0.31
  facet: contract_quality
  points: 20
  baseline_pass_rate: 0.949
  saturated: true
  saturated_note: >-
    95% of providers with a contract, docs and a reference already earn this; the vendor cannot move it
    for most of its buyers.
  cohort_pct: 96.4
  control_pct: 94.8
  delta_pp: 1.6
- feature: served-openapi
  check: spec_presence
  layer: agent_readiness
  conditional: true
  condition: Same as contract_present — only when the served spec is the provider's first OpenAPI.
  points: 18
  baseline_pass_rate: 1.0
  saturated: true
  saturated_note: >-
    100% of providers with a contract, docs and a reference already earn this; the vendor cannot move
    it for most of its buyers.
  cohort_pct: 100.0
  control_pct: 100.0
  delta_pp: 0.0
- feature: served-openapi
  check: openapi_3_1
  layer: composite
  conditional: true
  condition: >-
    Only when the served 3.1 document is the provider's published contract; version checks read the provider's
    original, so a 3.0 source re-served as 3.1 does not count.
  catalog_pass_rate: 0.414
  facet: contract_quality
  points: 5
  baseline_pass_rate: 0.411
  cohort_pct: 91.7
  control_pct: 40.8
  delta_pp: 50.9
- feature: sdk-idempotency
  check: idempotency
  layer: agent_readiness
  conditional: true
  condition: >-
    Only if the API already honours an idempotency key and the definition declares it; the SDK header
    cannot create server-side de-duplication.
  grade: documented
  points: 9
  baseline_pass_rate: 0.115
  cohort_pct: 15.0
  control_pct: 11.4
  delta_pp: 3.6
earns_nothing:
- feature: postman-generator
  check: postman_present
  why: >-
    Fern's Postman generator is deprecated; a collection now comes from the provider importing its own
    OpenAPI into Postman.
- feature: docs-mcp
  check: well_known_published
  why: >-
    The MCP server is advertised by page actions, not by any of the four well-known documents; only the
    api-catalog row earns this check.
out_of_reach:
  checks:
  - agent_card
  - rules_present
  - info_complete
  - operations_description_coverage
  - error_semantics
  - status_page_present
  note: >-
    Fern serves no A2A agent card and ships no governance ruleset; it cannot write the prose (info contact,
    operation descriptions) or the error model a contract is missing.
unscored_practice:
- feature: markdown-access
  why: >-
    Markdown twins and agent directives prepended to pages; no check reads agent-facing directives or
    markdown negotiation.
- feature: served-openapi
  why: >-
    A served AsyncAPI 2.6 and a contract linked from llms.txt are real agent-discovery practice the rubric
    scores only as a contract, not as its discoverability.
- feature: sdk-idempotency
  why: Webhook signature verification in generated SDKs is agent-safety practice no check reads.
surface:
  discoverability:
    reachable: 10.0
    total: 54
  contract_quality:
    reachable: 29.0
    total: 211
  operational_transparency:
    reachable: 6.0
    total: 38
  developer_ergonomics:
    reachable: 23.0
    total: 42
  agent_readiness:
    reachable: 41.5
    total: 139
hard_rule: >-
  A model, not a score. Adopting this vendor changes a provider's Kin Score only when the provider publishes
  the resulting artifacts on its own surface; nothing here writes a score, and no sponsorship or partnership
  can.
method: searched
source:
- https://buildwithfern.com/learn/cli-generator/get-started/overview
- https://buildwithfern.com/learn/docs/ai-features/ai-examples
- https://buildwithfern.com/learn/docs/ai-features/api-catalog
- https://buildwithfern.com/learn/docs/ai-features/host-skills
- https://buildwithfern.com/learn/docs/ai-features/llms-txt
- https://buildwithfern.com/learn/docs/ai-features/mcp-server
- https://buildwithfern.com/learn/docs/api-references/api-explorer
- https://buildwithfern.com/learn/docs/configuration/changelogs
- https://buildwithfern.com/learn/docs/developer-tools/openapi-spec
- https://buildwithfern.com/learn/docs/getting-started/capabilities
- https://buildwithfern.com/learn/docs/integrations/postman
- https://buildwithfern.com/learn/docs/llms.txt
- https://buildwithfern.com/learn/llms.txt
- https://buildwithfern.com/learn/sdks/overview/capabilities
measured:
  cohort:
    method: vendors-catalog.json detections (CNAME / header / URL shape / markup), never a name match
    detected: 29
    in_baseline: 21
  control:
    basis: providers earning contract_present + documentation_present + api_reference_present, minus the
      cohort
    n: 5195
  metric: >-
    cohort_pct / control_pct = mean share of the check's points earned (derived and platform credit weighted),
    x100
  measured_on: '2026-09-25'
  composite_mean:
    cohort: 54.1
    control: 48.0
  agent_readiness_mean:
    cohort: 40.1
    control: 32.5
  status: measured
  caveat: >-
    A cohort delta is association, not cause: customers choose a vendor for reasons that also move their
    score. Read it beside the capability map, never instead of it.
simulation:
  simulated_on: '2026-09-25'
  rubric: 0.23.0
  population: providers publishing a contract (contract_present earned), replayable exactly
  providers: 8977
  providers_unreplayable: 987
  providers_moved: 8977
  conditional_rows: excluded (they depend on what the API already does)
  composite_lift:
    median: 11.1
    p75: 12.9
    p90: 13.7
    max: 16.2
    mean_among_movers: 10.5
  agent_readiness_lift:
    median: 11.5
    p75: 13.6
    p90: 13.7
    max: 15.9
    mean_among_movers: 11.0
  facet_lift_median_among_movers:
    discoverability: 11.1
    contract_quality: 2.7
    operational_transparency: 15.8
    developer_ergonomics: 38.1
  composite_band_moves:
    thin -> developing: 2977
    developing -> strong: 2444
    strong -> exemplar: 756
    emerging -> thin: 367
    emerging -> developing: 58
    developing -> exemplar: 10
    minimal -> emerging: 3
    thin -> strong: 2
  agent_readiness_band_moves:
    agent-aware -> agent-ready: 4871
    agent-ready -> agent-native: 306
    agent-aware -> agent-native: 53
  method: >-
    each provider's own kin/checks file, the vendor's maps at their stated credit, the scorer's composite
    formula; from -> to, nothing written