MCP Tools Reference

Local Tools

These tools run locally via the @emailens/engine npm package. No account or API key needed.

preview_email

Full email compatibility preview , transforms HTML for 21 clients, analyzes CSS, generates scores, previews dark mode, checks inbox preview and email size.

Parameter	Type	Required	Description
`html`	`string`	Yes	The email HTML source code
`clients`	`string[]`	No	Filter to specific client IDs (e.g. `["gmail-web", "outlook-windows"]`)
`format`	`string`	No	`"html"` (default), `"jsx"`, `"mjml"`, or `"maizzle"`
`targetingPolicy`	`string`	No	`"progressive"` (default), `"strict"`, or `"lenient"`

Returns: overallScore, compatibilityScores, cssWarnings, inboxPreview, sizeReport, darkModeWarnings, plainText, clientCount.

When no API key is set and score is below 90, includes a tip field suggesting screenshots.

analyze_email

Quick CSS compatibility analysis: returns warnings and per-client scores. Faster than audit_email when you only need CSS compatibility.

Breaking change in v0.4.0: analyze_email now returns CSS-only results. Previously it returned the full audit (spam, links, a11y, images). Use audit_email for the full report.

Parameter	Type	Required	Description
`html`	`string`	Yes	The email HTML source code
`format`	`string`	No	Input format for framework-specific fix snippets
`clients`	`string[]`	No	Filter to specific client IDs
`detail`	`string`	No	How much of each finding to return
`targetingPolicy`	`string`	No	`"progressive"` (default), `"strict"`, or `"lenient"`

Returns: overallScore (the worst client's score), scores, warningCount, findingCount, findings.

Comprehensive quality audit: CSS compatibility, spam scoring, link validation, accessibility, images, inbox preview, size (Gmail clipping), template variables, content overflow, visual bugs, dark-mode and mobile text contrast, and design consistency.

The last three cover what a light desktop preview cannot show: text that vanishes when a client forces dark mode or when the email's own dark block repaints a surface without re-colouring the text on it, contrast below the email's breakpoint, and colours that differ by value but not to a reader.

Parameter	Type	Required	Description
`html`	`string`	Yes	The email HTML source code
`format`	`string`	No	Input format
`skip`	`string[]`	No	Checks to skip: `"spam"`, `"links"`, `"accessibility"`, `"images"`, `"compatibility"`, `"inboxPreview"`, `"size"`, `"templateVariables"`, `"overflow"`, `"visual"`, `"darkContrast"`, `"mobileContrast"`, `"design"`, `"vml"`, `"styleSurvival"`, `"targeting"`
`clients`	`string[]`	No	Filter to specific client IDs
`detail`	`string`	No	How much of each finding to return
`targetingPolicy`	`string`	No	`"progressive"` (default), `"strict"`, or `"lenient"`

Returns: overallCompatibility, compatibility, spam, links, accessibility, images, inboxPreview, size, templateVariables, overflow, visual, vml, darkContrast, mobileContrast, design, styleSurvival, targeting.

fix_email

Generate a structured fix prompt for email compatibility issues. Returns markdown with fix instructions that the AI can apply directly.

Parameter	Type	Required	Description
`html`	`string`	Yes	The email HTML source code to fix
`format`	`string`	No	Controls fix syntax
`scope`	`string`	No	`"all"` (default) or `"current"` (requires `selectedClientId`)
`selectedClientId`	`string`	No	Client ID to scope fixes to

Returns: totalWarnings, structuralWarnings, cssWarnings, tokenEstimate, and the fix prompt as a second content block.

diff_emails

Compare two email HTML versions , shows score changes, fixed issues, and newly introduced issues per client.

Parameter	Type	Required	Description
`before`	`string`	Yes	Original email HTML
`after`	`string`	Yes	Modified email HTML
`format`	`string`	No	Input format

Returns: results (per-client diff with scoreBefore, scoreAfter, scoreDelta, fixed, introduced, unchanged) and summary (clientsImproved, clientsRegressed, clientsUnchanged, avgScoreDelta).

check_deliverability

Check email deliverability for a domain , SPF, DKIM, DMARC, MX, and BIMI records.

Parameter	Type	Required	Description
`domain`	`string`	Yes	Domain to check (e.g. `"company.com"`)

Returns: domain, score (0-100), checks (per-record status), issues.

Uses DNS lookups , no API key needed. Requires @emailens/engine >= 0.9.1.

list_clients

List all 21 supported email clients.

No parameters.

Returns an array of { id, name, category, engine, darkModeSupport, deprecated? }.

Hosted Tools

These tools require the EMAILENS_API_KEY environment variable. Without it, they return a setup guide instead of an error.

capture_screenshots

Generate visual email previews across 21 clients using headless browsers. Previews are hosted on CDN.

Parameter	Type	Required	Description
`html`	`string`	Yes	The email HTML source code
`format`	`string`	No	Input format
`clients`	`string[]`	No	Filter to specific client IDs
`modes`	`string[]`	No	`["light"]` (default), `["dark"]`, or `["light", "dark"]`
`title`	`string`	No	Name for the hosted preview

Returns: previewId, previewUrl, overallScore, screenshots (client-mode to URL map), screenshotStatus, captured, failed.

Free plan: 30 live previews/day. Dev plan: 100/day. Pro plan: unlimited.

share_preview

Create a shareable link for an email preview. Recipients see the full analysis without needing an account.

Parameter	Type	Required	Description
`html`	`string`	Yes	The email HTML source code
`title`	`string`	No	Display title
`format`	`string`	No	Input format

Returns: shareUrl, expiresAt.

Requires Dev plan ($9/mo). Dev: 7-day expiry. Pro: permanent links.

Sandbox tools

Four tools drive the SMTP sandbox, so an agent can send a real email from your app and read what arrived. See Sandbox for AI agents for the workflow.

Tool	Parameters	Description
`sandbox_get_inbox`	`name`	Get or create a sandbox inbox and its SMTP credentials
`sandbox_list_messages`	`inboxId`	List the emails captured in an inbox
`sandbox_wait_for_email`	`inboxId`, `subject`, `sender`, `timeoutSeconds`	Block until a matching email arrives
`sandbox_get_message`	`messageId` (required)	Full message: HTML and text parts, headers, extracted OTP and magic links, spam analysis

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