Agent Skill · Sinch

sinch-mailgun-inspect

Checks email quality before sending via Mailgun Inspect API. Use when previewing emails across clients, checking accessibility (WCAG), validating links, validating images, or analyzing email HTML/CSS compatibility.

View SKILL.md on GitHub → Source repository Provider profile
Provider: Sinch Path in repo: skills/sinch-mailgun-inspect/SKILL.md

Skill body

Mailgun Inspect

Overview

Mailgun Inspect (by Sinch) is an email pre-send quality control API. Five capabilities:

Capability Base Path Input
Accessibility /v1/inspect/accessibility html + encoded
Link Validation /v1/inspect/links links URL array (or /html-validate for HTML)
Image Validation /v1/inspect/images links URL array (or /html-validate / /upload)
Code Analysis /v1/inspect/analyze html (no encoded field)
Email Previews /v1/preview/tests (V1) / /v2/preview/tests (V2) varies

For full endpoint tables and request schemas, see references/api-endpoints.md.

Agent Instructions

Before generating code, gather from the user (skip any item already specified in the prompt or context):

  1. Scope — broad QC (run all four HTML-based tests in parallel) or a specific capability (e.g. “check links” → run only that one)?
  2. Input method — raw HTML, a list of URLs, or an image file? Route to the correct endpoint per the capability table.
  3. Region — US or EU? Must match the user’s Mailgun account.
  4. Language — any language, or curl. This API is REST-only; there is no SDK wrapper.

Product gotchas to apply unconditionally:

Refer to the API references linked in Links for request/response schemas.

Security: See the Security section below for url fetching policy and credential handling.

Getting Started

Agent Credentials handling

Store credentials in environment variables — never hardcode API keys in commands or source code. In scripts and CI, inject the key via MAILGUN_API_KEY (or your platform’s secret mechanism), not literals in the job definition. Do not paste live keys into shell commands that may be logged, shared, or committed.

export MAILGUN_API_KEY="your-private-api-key"

Authentication

Ensure that authentication headers are properly set when making API calls. Mailgun Inspect uses HTTP Basic Auth — username api, password your Mailgun Private API key:

--user "api:$MAILGUN_API_KEY"

Keep the Mailgun private API key in environment variables or a secret manager. Avoid generating commands or code that embed the key next to --user except via a variable (as in the example above).

See the sinch-authentication skill for full auth setup.

Base URLs

Region Endpoint
US api.mailgun.net
EU api.eu.mailgun.net

Async Workflow – Critical

Create responses may return "status": "Processing" or "Completed" depending on endpoint/workload. You must poll the GET endpoint until status is "Complete" or "Completed" (treat "Failed" as terminal error) to get actual results.

Canonical Example: Accessibility Test

# 1. Create test (returns 201 + test ID)
curl -X POST \
  "https://api.mailgun.net/v1/inspect/accessibility" \
  --user "api:$MAILGUN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"html": "<html><body><h1>Hello</h1><img src=\"logo.png\"></body></html>", "encoded": false}'

# 2. Poll for results (repeat until status is "Complete" or "Completed"; "Failed" = error)
curl -X GET \
  "https://api.mailgun.net/v1/inspect/accessibility/TEST_ID" \
  --user "api:$MAILGUN_API_KEY"

All other endpoints follow the same create-then-poll pattern. Adapt the path and request body per the capability table above. For programmatic use, prefer the Node.js SDK from the authentication skill so the key is not interpolated into command strings.

Key Concepts

Choosing the Right Input Method

Each capability accepts different input types. Pick the right one:

Endpoint Path Gotchas

These paths are commonly confused:

Response Lifecycle

  1. POST returns {"meta": {"status": "Processing"}, "items": {"id": "abc123", ...}}
  2. GET poll until status is "Complete" or "Completed" (treat "Failed" as terminal error)
  3. DELETE clean up when done

Accessibility POST returns 201. All other POSTs return 200.

Common Patterns

Full Pre-Send Check

For a complete email quality check, fire all four HTML-based tests in parallel, then poll each:

  1. POST /v1/inspect/accessibility – body: {"html": "...", "encoded": false}
  2. POST /v1/inspect/links/html-validate – body: {"html": "..."}
  3. POST /v1/inspect/images/html-validate – body: {"html": "..."}
  4. POST /v1/inspect/analyze – body: {"html": "..."}
  5. Poll each GET /v1/inspect/{category}/{test_id} until complete

V2 shortcut: If also generating email previews, POST /v2/preview/tests can trigger all four content checks in one call by including content-checking fields in the request body. See references/api-endpoints.md § Email Previews.

CI/CD Gate

Create test, poll until complete, parse results, fail build on critical issues. See the canonical example above for the create-and-poll pattern. Use jq to extract status and results for scripting.

Image Optimization

After validating images, optimize them:

Code Analysis Filtering

Filter results by client support when retrieving code analysis:

GET /v1/inspect/analyze/{id}?support_type=n&application_type=web

Values: support_type = y/a/n/u (yes/anomaly/no/unknown), application_type = web/mobile/desktop.

Gotchas and Best Practices

  1. Content-Type – All requests use application/json (not form data like Mailgun Send).
  2. Async results – Creates may return "Processing" or "Completed" depending on endpoint/workload. Always check the status before assuming results are available.
  3. Accessibility returns 201 – All other creates return 200.
  4. Input types differ – Only accessibility uses html + encoded. Links and images take a links URL array. Code analysis takes html without encoded. Using the wrong body silently fails.
  5. /html-validate for HTML input – If you have HTML (not URLs), use the /html-validate sub-endpoint for links and images.
  6. Same auth as Mailgun Send – No separate credentials. Same API key, same Basic Auth.
  7. Region consistency – Use the same region (US or EU) as your Mailgun Send account.
  8. Pagination – List endpoints support limit (max 1000, default 100) and skip (default 0).

Security

Skill frontmatter

metadata: {"author" => "Sinch", "version" => "1.0.5", "category" => "Email", "tags" => "email, mailgun, inspect, accessibility, links, images, previews, qa", "uses" => ["sinch-authentication"]}