Email on Acid

Email on Acid (now branded as Mailgun Inspect) is an email testing and pre-deployment quality assurance platform with a REST API for rendering email previews across 100+ email clients and devices, checking accessibility compliance (WCAG 2.2), validating HTML/CSS compatibility, running spam filter analysis, and automating pre-send email testing workflows via HTTP Basic Authentication.

Email on Acid publishes 4 API contracts indexed on the APIs.io network, including Authentication API, Email Clients API, Email Testing API, and 1 more. Tagged areas include Email Testing, Email Previews, Email Client, Spam Testing, and Accessibility.

The Email on Acid catalog on APIs.io includes 1 JSON-LD context and 1 Spectral governance ruleset.

Email on Acid’s developer surface includes authentication, documentation, engineering blog, pricing, and 12 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

36.9/100 thin ▬ flat Agent 24/100 agent aware Front door AI 1/6 silent saas Full breakdown ↓
scored 2026-11-06 · rubric v0.27.0 · Show this score on your site →

AccessPaid

1 published contract

Email TestingEmail PreviewsEmail ClientSpam TestingAccessibilityHTML ValidationEmail Quality AssurancePre-Deployment Testing

Kin Score

Kin Score How this is scored →
scored 2026-11-06 · rubric v0.27.0

Composite quality — 36.9/100 · thin

Contract Quality 11.2 / 19

Developer Ergonomics 3.8 / 15

Access Clarity 3.9 / 15

Operational Transparency 2.8 / 10

Contract Governance 0.9 / 9

Discoverability 5.0 / 8

Regulatory Posture 3.2 / 15

Create-or-Update Ergonomics 0.0 / 10

Agent readiness — 24/100 · agent aware

Machine-Readable Contract 18 / 18

Agentic Access Contract 10 / 10

Documented Reversibility 0 / 6

MCP Server 0 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 7 / 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 4 / 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 0 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

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 applies to this provider. This API accepts writes, so it carries 10 points of the composite. It is scored from the published contracts themselves: whether a caller can create-or-update in one call, whether the write accepts a key the caller already holds, and whether the response says which branch ran. Without that, every write needs a search-and-branch in front of it, and the first time that check is skipped a duplicate record is created. Scored against the observed mean rather than raw — a provider at the catalog average is unchanged by this facet, not penalised by it.

The six quality facets above are damped to 75 points between them, because the conditional facet above carries the other 25. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 75% 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):

MCP Server +12 pts — deployment.mode + probe verdict on the mcp/ manifest, not the pointer; an unprobed slug falls back to authorship
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)
Stable Error Semantics +8 pts — OpenAPI $refs a shared error schema across 4xx/5xx responses (verified), else common[].type includes ErrorCatalog / ErrorCodes / DeclineCodes
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0
Registration Without a Human +6 pts — a `registration_endpoint` in the served RFC 8414 / OIDC discovery document
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)

8 more unmet checks in the Agent Readiness table above.

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

Developer Ergonomics scores 25.0 — up to +15.0 composite points
Access Clarity scores 26.3 — up to +14.7 composite points
Contract Governance scores 9.8 — up to +10.8 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/email-on-acid/apis.yml: open an issue on github.com/api-evangelist/email-on-acid 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 →

Markets this provider is in provisional

The Kin Score Market layer reads a provider inside its market: its position, and how deep its integrations go. Depth is only comparable within a position. Provisional and unweighted: not part of the Kin Score or agent readiness.

Market	Position	Depth	Registered MCP server	Declares compatibility
Digital Accessibility (IAAP membership, W3C WAI evaluation tools)	undeclared	-	-	-

Registered MCP server and declares compatibility are report only — not weighted. Undeclared means we found nothing we can read, so there is no number: we never infer integrations.

Standards implemented 1

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

OpenAPI

measured — observed by APIs.io (published)

APIs 4

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

Email on Acid Authentication API

Verify API credentials

Email on Acid Email Clients API

Manage email client lists and defaults for testing

Email on Acid Email Testing API

Create and manage email rendering tests

Email on Acid Spam Testing API

Standalone spam filter analysis and seed list management

Open Collections 4

Open, tool-agnostic API collections (OpenAPI-derived and Bruno).

Email on Acid Authentication API

OPEN COLLECTION

Email on Acid Authentication Email Clients API

OPEN COLLECTION

Email on Acid Authentication Email Testing API

OPEN COLLECTION

Email on Acid Authentication Spam Testing API

OPEN COLLECTION

Email on Acid API pricing

Not yet checked against Email on Acid's own pricing page. Compiled by API Evangelist; confirm before you rely on a figure.

Plan	Price
Basic	$99.0
Premium	$199.0
Contract	—

Plan details, limits and sources →

Rate limits

Monthly Email Previews - Basic Plan: 1000 monthly
Monthly Email Previews - Premium Plan: 2000 monthly
Monthly Email Previews - Contract Plan: custom monthly

Compiled by API Evangelist, not yet checked against Email on Acid's documentation. All 4 limits →

Pricing Plans 1

Published pricing tiers and plan structures.

Email On Acid Plans Pricing

3 plans

PLANS

Rate Limits 1

Documented rate limits and quota policies.

Email On Acid Rate Limits

4 limits

RATE LIMITS

Service Levels 1

Uptime the provider promises or reports, as SLA4OAI. Read from its own pages; APIs.io runs no monitors.

Email on Acid

SLA

FinOps 1

Cost, billing, and metering signals for API financial operations.

Email On Acid Finops

FINOPS

Semantic Vocabularies 1

JSON-LD contexts and semantic vocabularies used across these APIs.

Email On Acid Context

9 classes · 46 properties

JSON-LD

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs.

Email on Acid — jsonschema rules

5 rules · 4 warnings 1 info

SPECTRAL

JSON Schema 3

Standalone JSON Schema definitions for this provider's data models.

CreateEmailTestRequest

13 properties

JSON SCHEMA

EmailTestResult

0 properties

JSON SCHEMA

CreateSpamTestRequest

12 properties

JSON SCHEMA

Examples 4

Example request and response payloads for these APIs.

Create Email Test

7 fields

EXAMPLE

Create Spam Test

6 fields

EXAMPLE

Email Test Response

4 fields

EXAMPLE

Email Test Results

3 fields

EXAMPLE

Security Posture 3

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

Email On Acid Authentication

http · 1 scheme

SECURITY

Email On Acid Domain Security

TLSv1.3 · HSTS · DMARC

SECURITY

Email On Acid Trust Center

SOC 2, ISO 27001, GDPR

SECURITY

Agentic Access 1

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

Email On Acid Agentic Access

23 operations · 6 acting

AGENTIC

Resources

Documentation 1

Reference material describing how the API behaves

Documentation

Documentation

Agent Surfaces 1

MCP servers, agent skills, and machine-readable catalogs

AgenticAccess

AgenticAccess

Build 2

SDKs, sample code, and the tooling you integrate with

PostmanWorkspace

PostmanWorkspace

GitHubOrg

GitHubOrg

Access & Security 3

Authentication, authorization, and security posture

TrustCenter

TrustCenter

DomainSecurity

DomainSecurity

Authentication

Authentication

Operate 2

Status, limits, changes, and where to get help

StatusPage

StatusPage

RateLimits

RateLimits

Commercial 3

Pricing, plans, and the legal terms of use

Pricing

Pricing

Plans

Plans

FinOps

FinOps

Company 3

The organization behind the API

Website

Website

LinkedIn

Blog

Blog

Other 1

Properties that don't map to a standard resource type

Source (apis.yml)

name: Email on Acid
description: Email on Acid (now branded as Mailgun Inspect) is an email testing and pre-deployment quality assurance platform
  with a REST API for rendering email previews across 100+ email clients and devices, checking accessibility compliance (WCAG
  2.2), validating HTML/CSS compatibility, running spam filter analysis, and automating pre-send email testing workflows via
  HTTP Basic Authentication.
deliveryModel:
  model: saas
  open_source: false
  commercial: true
  callable_host: true
  label: Hosted service · you call their endpoint
  confidence: high
  source:
  - openapi
  - pricing
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: paid
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Paid
  confidence: medium
  source:
  - plans
  - authentication
  - security
  generated: '2026-11-06'
  method: derived
image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/icons/email-on-acid.png
url: https://raw.githubusercontent.com/api-evangelist/email-on-acid/refs/heads/main/apis.yml
created: '2026-06-13'
modified: '2026-06-13'
specificationVersion: '0.23'
aid: email-on-acid
type: Index
tags:
- Email Testing
- Email Previews
- Email Client
- Spam Testing
- Accessibility
- HTML Validation
- Email Quality Assurance
- Pre-Deployment Testing
tags_raw:
- Email Testing
- Email Previews
- Email Clients
- Spam Testing
- Accessibility
- HTML Validation
- Email Quality Assurance
- Pre-Deployment Testing
apis:
- aid: email-on-acid:email-on-acid-authentication-api
  name: Email on Acid Authentication API
  description: Verify API credentials
  humanURL: https://api.emailonacid.com/docs/latest
  baseURL: https://api.emailonacid.com/v5
  tags:
  - Authentication
  properties:
  - type: OpenAPI
    url: openapi/email-on-acid-authentication-api-openapi.yml
  - type: Documentation
    url: https://api.emailonacid.com/docs/latest
- aid: email-on-acid:email-on-acid-email-clients-api
  name: Email on Acid Email Clients API
  description: Manage email client lists and defaults for testing
  humanURL: https://api.emailonacid.com/docs/latest
  baseURL: https://api.emailonacid.com/v5
  tags:
  - Email Client
  tags_raw:
  - Email Clients
  properties:
  - type: OpenAPI
    url: openapi/email-on-acid-email-clients-api-openapi.yml
  - type: Documentation
    url: https://api.emailonacid.com/docs/latest
- aid: email-on-acid:email-on-acid-email-testing-api
  name: Email on Acid Email Testing API
  description: Create and manage email rendering tests
  humanURL: https://api.emailonacid.com/docs/latest
  baseURL: https://api.emailonacid.com/v5
  tags:
  - Email Testing
  properties:
  - type: OpenAPI
    url: openapi/email-on-acid-email-testing-api-openapi.yml
  - type: Documentation
    url: https://api.emailonacid.com/docs/latest
- aid: email-on-acid:email-on-acid-spam-testing-api
  name: Email on Acid Spam Testing API
  description: Standalone spam filter analysis and seed list management
  humanURL: https://api.emailonacid.com/docs/latest
  baseURL: https://api.emailonacid.com/v5
  tags:
  - Spam Testing
  properties:
  - type: OpenAPI
    url: openapi/email-on-acid-spam-testing-api-openapi.yml
  - type: Documentation
    url: https://api.emailonacid.com/docs/latest
common:
- type: PostmanWorkspace
  url: https://www.postman.com/kinlaneapi/email-on-acid/overview
- type: AgenticAccess
  url: agentic-access/email-on-acid-agentic-access.yml
- type: TrustCenter
  url: security/email-on-acid-trust-center.yml
- type: DomainSecurity
  url: security/email-on-acid-domain-security.yml
- type: Authentication
  url: authentication/email-on-acid-authentication.yml
- type: Website
  url: https://www.emailonacid.com
- type: Documentation
  url: https://api.emailonacid.com/docs/latest
- type: GitHubOrg
  url: https://github.com/emailonacid
- type: LinkedIn
  url: https://www.linkedin.com/company/email-on-acid
- type: Blog
  url: https://www.emailonacid.com/blog/
- type: Pricing
  url: https://www.emailonacid.com/pricing/
- type: StatusPage
  url: https://status.emailonacid.com/
- type: X
  url: https://twitter.com/EmailOnAcid
- type: Plans
  url: plans/email-on-acid-plans-pricing.yml
- type: RateLimits
  url: rate-limits/email-on-acid-rate-limits.yml
- type: FinOps
  url: finops/email-on-acid-finops.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com

Email on Acid API — frequently asked questions

Does Email on Acid have an API?

Yes. APIs.io lists 4 APIs from Email on Acid, including Email on Acid Authentication API, Email on Acid Email Clients API and Email on Acid Email Testing API, and 1 more.

Is there an OpenAPI specification for the Email on Acid API?

Yes. APIs.io indexes 4 OpenAPI specifications for Email on Acid, each linked for download from this page.

How do I authenticate with the Email on Acid API?

Email on Acid uses bearer-token authentication (http · 1 scheme). The details are profiled on APIs.io as Email On Acid Authentication.

How much does the Email on Acid API cost?

APIs.io lists 3 pricing plans for Email on Acid, with each plan's price, limits and inclusions under Pricing on this page.

Is the Email on Acid API ready for AI agents?

Email on Acid has a Kin Score of 36.9 out of 100 (thin) and an Agent Readiness score of 24.1 (agent-aware), scored by API Evangelist on 2026-11-06.

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