subdomain-app

Subdomain API provides a free, no‑signup JSON API that returns the subdomains associated with any given domain. Leveraging one of the largest publicly available subdomain indexes, the service enables developers and security researchers to automate discovery, enrich threat intelligence, and integrate subdomain enumeration into CI/CD pipelines. The API is publicly accessible via HTTPS GET requests and returns results in a simple JSON array, making it easy to consume in scripts and applications.

subdomain-app is listed with 1 API on the APIs.io network. Tagged areas include Security, Subdomain, Discovery, API, and Free.

The subdomain-app catalog on APIs.io includes 1 Spectral governance ruleset.

🌐 Visit website 📡 Profile data on GitHub

23.1/100 emerging Agent 15/100 agent aware Full breakdown ↓
scored 2026-10-31 · rubric v0.25.0 · Show this score on your site →

1 API

SecuritySubdomainDiscoveryAPIFree

Kin Score

Kin Score How this is scored →
scored 2026-10-31 · rubric v0.25.0

Composite quality — 23.1/100 · emerging

Contract Quality 0.0 / 21

Developer Ergonomics 0.0 / 17

Access Clarity 3.6 / 17

Operational Transparency 2.1 / 11

Contract Governance 6.7 / 10

Discoverability 5.6 / 9

Regulatory Posture 4.3 / 15

Agent readiness — 15/100 · agent aware

Machine-Readable Contract 0 / 18

Agentic Access Contract 10 / 10

Documented Reversibility 0 / 6

MCP Server 12 / 12

Machine-Readable Auth 0 / 10

Idempotency 0 / 9

Stable Error Semantics 8 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 7 / 7

Typed Event Surface 0 / 6

Agent Skills 0 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 5 / 5

Distinct Operations 3 / 3

Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics could not be measured. We hold no machine-readable contract for this provider to read, so there is nothing to measure a write surface against. Excluded rather than scored zero: never-measured and measured-empty are different facts. Publishing an OpenAPI is what makes this facet — and several others — scorable at all.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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Agent readiness — checks not met, largest first (exact, from this profile):

Machine-Readable Contract +18 pts — api_specs includes an OpenAPI document
Machine-Readable Auth +10 pts — a served openid-configuration/oauth-authorization-server carrying `issuer` (served), else the securitySchemes class in the provider OpenAPIs — bound (mutualTLS, DPoP, Signature) > negotiable (oauth2 authorizationCode/clientCredentials, openIdConnect) > bearer (http bearer, apiKey)
Idempotency +9 pts — OpenAPI mutating operations declare an idempotency key — a header, a request-body property, or a named de-duplication token whose own description says so (verified); else common[].type matches /idempoten/i (documented)
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0
Request/Response Examples +7 pts — share of operations carrying request/response examples; else an Examples / Code Samples link
Delegated User Identity +6 pts — a served discovery document listing authorization_code in grant_types_supported (served), else an oauth2 authorizationCode flow or openIdConnect declared in an OpenAPI (documented)

9 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Contract Quality scores 0.0 — up to +25.0 composite points
Developer Ergonomics scores 0.0 — up to +20.0 composite points
Access Clarity scores 21.1 — up to +15.8 composite points

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/subdomain-app/apis.yml: open an issue on github.com/api-evangelist/subdomain-app to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

APIs 1

Individual APIs this provider publishes, each with its own machine-readable definition.

Subdomain API

Find the subdomains of a domain name.

Pricing Plans 1

Published pricing tiers and plan structures.

Subdomain App Plans Pricing

0 plans

PLANS

Rate Limits 1

Documented rate limits and quota policies.

Subdomain App Rate Limits

1 limits

RATE LIMITS

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs.

subdomain-app API Rules

10 rules · 8 errors 1 warnings 1 info

SPECTRAL

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Subdomain App Authentication

0 schemes

SECURITY

Subdomain App Domain Security

TLSv1.3 · HSTS · DNSSEC · DMARC

SECURITY

Scopes 1

OAuth scopes governing access to this provider's APIs.

Subdomain App Scopes

OAuth 2.0 · no documented scopes

0 scopes

SCOPES

Agentic Access 1

Recommended x-agentic-access execution contracts for AI agents.

Subdomain App Agentic Access

1 operation

1 operations · 0 acting

AGENTIC

Resources

Agent Surfaces 1

MCP servers, agent skills, and machine-readable catalogs

AgenticAccess

AgenticAccess

Design & Contract 3

Pagination, idempotency, versioning, errors, and events

Spectral

Spectral

ErrorCatalog

ErrorCatalog

Conformance

Conformance

Access & Security 1

Authentication, authorization, and security posture

DomainSecurity

DomainSecurity

Operate 1

Status, limits, changes, and where to get help

RateLimits

RateLimits

Commercial 2

Pricing, plans, and the legal terms of use

TermsOfService

TermsOfService

PrivacyPolicy

PrivacyPolicy

Company 1

The organization behind the API

Website

Website

Other 2

Properties that don't map to a standard resource type

Hosts

Hosts

Vendors

Vendors

Source (apis.yml)

aid: subdomain-app
name: subdomain-app
description: Subdomain API provides a free, no‑signup JSON API that returns the subdomains associated with any given domain.
  Leveraging one of the largest publicly available subdomain indexes, the service enables developers and security researchers
  to automate discovery, enrich threat intelligence, and integrate subdomain enumeration into CI/CD pipelines. The API is
  publicly accessible via HTTPS GET requests and returns results in a simple JSON array, making it easy to consume in scripts
  and applications.
url: https://artifacts.apis.io/subdomain-app/apis.yml
image: https://subdomain.app/favicon.svg
x-type: company
x-source: harvest:mcp-registry
x-tier: profiled
x-tier-reason: enrichment pass 2026-10-31 (modular-v1; was harvest)
specificationVersion: '0.20'
created: '2026-10-31'
modified: '2026-10-31'
tags:
- Security
- Subdomain
- Discovery
- API
- Free
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: AgenticAccess
  url: agentic-access/subdomain-app-agentic-access.yml
- type: RateLimits
  url: rate-limits/subdomain-app-rate-limits.yml
- type: Spectral
  url: rules/subdomain-app-rules.yml
- type: ErrorCatalog
  url: errors/subdomain-app-problem-types.yml
- type: Conformance
  url: conformance/subdomain-app-conformance.yml
- type: Hosts
  url: hosts/subdomain-app-hosts.yml
- type: Vendors
  url: vendors/subdomain-app-vendors.yml
- type: TermsOfService
  url: https://subdomain.app/terms
- type: PrivacyPolicy
  url: https://subdomain.app/privacy
- type: DomainSecurity
  url: security/subdomain-app-domain-security.yml
- type: Website
  url: https://subdomain.app/
apis:
- name: Subdomain API
  description: Find the subdomains of a domain name.
  humanURL: https://subdomain.app/
  baseURL: https://api.subdomain.app
  aid: subdomain-app:subdomain-api
x-enrichment:
  date: '2026-10-31'
  status: enriched
  artifacts_added: 23
  pass: modular-v1
  engine: identity=oss,contract=oss,surfaces=oss,docs=oss,regulatory=oss

subdomain-app API — frequently asked questions

Does subdomain-app have an API?

Yes. APIs.io lists 1 API from subdomain-app, including Subdomain API.

How do I authenticate with the subdomain-app API?

subdomain-app documents its authentication (0 schemes). The details are profiled on APIs.io as Subdomain App Authentication.

Is the subdomain-app API ready for AI agents?

subdomain-app has a Kin Score of 23.1 out of 100 (emerging) and an Agent Readiness score of 15.0 (agent-aware), scored by API Evangelist on 2026-10-31.

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