horizOn MCP Server

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by ProjectMakersDE

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TypeScript

Remote

Get Email Status

horizon_get_email_status

Read-onlyIdempotent

Check a queued email's delivery status (pending, processing, sent, or failed) and get failure details. Requires the email ID returned when the email was queued.

Instructions

Returns the delivery status (pending, processing, sent or failed) and details of one email queued with horizon_send_email. Use when: checking whether a sent or scheduled email was delivered, or why it failed. Not for: sending again (use horizon_send_email only for a new email) or stopping delivery (use horizon_cancel_email). Requires: the emailId from horizon_send_email. Side effects: None (read only). Returns: {id, status, templateSlug, userId, language, scheduledAt, processedAt, errorReason, createdAt}; errorReason explains a failed email (for example SMTP rejected it). Errors: An unknown emailId or one of another API key is rejected: pass the id returned by horizon_send_email. Needs HORIZON_API_KEY. Every failure returns an error result (isError) with the HTTP status and body: a 401 that horizon_test_connection also returns means HORIZON_API_KEY is wrong, 429 means the account's per-minute rate limit was reached (wait a minute, then retry).

Input Schema

TableJSON Schema

Name	Required	Description	Default
`emailId`	Yes	Email ID (UUID) returned by horizon_send_email

Output Schema

TableJSON Schema

Name	Required	Description	Default
`id`	No
`status`	No
`userId`	No
`language`	No
`createdAt`	No
`errorReason`	No
`processedAt`	No
`scheduledAt`	No
`templateSlug`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv1.6.0Oct 2, 2026

changedInput schema / properties / emailId / description

Previous value: -"ID of the email to check (returned by send_email)"New value: +"Email ID (UUID) returned by horizon_send_email"

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": {},
+  "properties": {
+    "createdAt": {
+      "anyOf": [
+        {
+          "description": "When the email was queued",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "errorReason": {
+      "anyOf": [
+        {
+          "description": "Why sending failed, null unless failed",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "id": {
+      "anyOf": [
+        {
+          "description": "Email ID",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "language": {
+      "anyOf": [
+        {
+          "description": "Template language",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "processedAt": {
+      "anyOf": [
+        {
+          "description": "When the email was processed, null while pending",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "scheduledAt": {
+      "anyOf": [
+        {
+          "description": "Scheduled send time, null for immediate",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "status": {
+      "anyOf": [
+        {
+          "description": "pending, processing, sent or failed",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "templateSlug": {
+      "anyOf": [
+        {
+          "description": "Template used",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "userId": {
+      "anyOf": [
+        {
+          "description": "Recipient user ID",
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    }
+  },
+  "type": "object"
+}

First observedv1.5.4Sep 28, 2026

TDQS

A4.8/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover readOnly/idempotent/destructive, but the description adds substantial context beyond them: auth requirement (HORIZON_API_KEY), rate-limit behavior (429 per-minute, wait and retry), 401 meaning, and cross-API-key id rejection. These are genuine behavioral disclosures the annotations do not provide.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Uses labeled sections (Use when / Not for / Requires / Side effects / Returns / Errors) with the purpose front-loaded, so scanning is fast. It is somewhat verbose, and restating the return fields is arguably redundant given an output schema exists, but no sentence is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a single-parameter read tool this covers everything an agent needs: selection criteria, prerequisites, side-effect profile, error taxonomy with remediation, and return shape. Output schema exists, yet the description's return summary is a harmless supplement rather than a gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the schema already documents emailId as the UUID returned by horizon_send_email, so the baseline is 3. The description adds that an unknown id or one belonging to another API key is rejected, which is a real invocation constraint beyond the schema text.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Returns the delivery status... of one email queued with horizon_send_email') and enumerates the possible status values. It explicitly distinguishes itself from the siblings horizon_send_email and horizon_cancel_email, so an agent can select it without ambiguity.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit when-to-use ('checking whether a sent or scheduled email was delivered, or why it failed') and when-not-to-use with named alternatives ('Not for: sending again... or stopping delivery...'). This is the full when/when-not/alternative triple.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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