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 APIs 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 Clients, 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 11 more developer resources.

🌐 Visit website 📡 Source on GitHub

46.8/100 developing ▬ flat Agent 22/100 agent aware saas Full breakdown ↓
scored 2026-09-08 · rubric v0.20.0

AccessPaid

1 APIs

Email TestingEmail PreviewsEmail ClientsSpam TestingAccessibilityHTML ValidationEmail Quality AssurancePre-Deployment Testing

Kin Score

Kin Score How this is scored →
scored 2026-09-08 · rubric v0.20.0

Composite quality — 46.8/100 · developing

Contract Quality 14.7 / 23

Developer Ergonomics 4.3 / 18

Access Clarity 10.4 / 18

Operational Transparency 6.2 / 12

Contract Governance 1.1 / 11

Discoverability 6.2 / 9

Create-or-Update Ergonomics 0.0 / 10

Agent readiness — 22/100 · 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 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

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.

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 github.com/api-evangelist/email-on-acid: open an issue to ask a question, or submit a pull request to add artifacts. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

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 5

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

API Collection

OPEN COLLECTION

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

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

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 API 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 1

SDKs, sample code, and the tooling you integrate with

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: '2026-09-03'
  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 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 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: 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

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