email59

Send an email

send_email

Send one email to one recipient: transactional (receipt, code, alert) or marketing (category). It goes out as HTML in a branded template with a text part; give text, html or both. Uses 1 email of today's allowance. Many recipients at once: send_campaign.

Input Schema

Name	Required	Description
`to`	Yes	Recipient address.
`code`	No	The code for template code.
`from`	No	Name before the @ (e.g. hello). The domain is always email59.com. Optional.
`html`	No	HTML body.
`text`	No	Plain-text body. Give text, html or both.
`brand`	No	This email's look; the account's brand otherwise.
`heading`	No
`list_id`	No	Marketing only: your name for the audience.
`subject`	Yes
`category`	No	Default transactional. marketing: always has the unsubscribe link and skips role addresses and people who unsubscribed.
`reply_to`	No	Optional. One address of your own (not at email59.com) where answers should go. Without it the email says replies are not received.
`template`	No	Layout. basic (default), code (one-time code, give code), notice (heading and one button), report (wide tables), letter (personal).
`preheader`	No	Preview text shown after the subject.
`button_url`	No
`button_text`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed9 schema fields changedOct 19, 2026

addedInput schema / properties / brand

Added value: +{
+  "description": "This email's look; the account's brand otherwise.",
+  "properties": {
+    "address": {
+      "type": "string"
+    },
+    "color": {
+      "type": "string"
+    },
+    "logo_url": {
+      "type": "string"
+    },
+    "name": {
+      "type": "string"
+    },
+    "url": {
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

addedInput schema / properties / button_text
```
Added value: +{
+  "type": "string"
+}
```
addedInput schema / properties / button_url
```
Added value: +{
+  "type": "string"
+}
```

addedInput schema / properties / category

Added value: +{
+  "description": "Default transactional. marketing: always has the unsubscribe link and skips role addresses and people who unsubscribed.",
+  "enum": [
+    "transactional",
+    "marketing"
+  ],
+  "type": "string"
+}

addedInput schema / properties / code

Added value: +{
+  "description": "The code for template code.",
+  "type": "string"
+}

addedInput schema / properties / heading
```
Added value: +{
+  "type": "string"
+}
```

addedInput schema / properties / list_id

Added value: +{
+  "description": "Marketing only: your name for the audience.",
+  "type": "string"
+}

addedInput schema / properties / preheader

Added value: +{
+  "description": "Preview text shown after the subject.",
+  "type": "string"
+}

addedInput schema / properties / template

Added value: +{
+  "description": "Layout. basic (default), code (one-time code, give code), notice (heading and one button), report (wide tables), letter (personal).",
+  "enum": [
+    "basic",
+    "code",
+    "notice",
+    "report",
+    "letter"
+  ],
+  "type": "string"
+}

First observedOct 15, 2026

TDQS

A4.4/5.0

Behavior4/5

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

Annotations already cover read-only, idempotency, open-world, and destructive hints. The description adds useful delivery behavior: HTML branded template with a text part, text/html/both guidance, and a quota consumption rule ('Uses 1 email of today's allowance'). It does not contradict annotations.

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

Conciseness5/5

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

Front-loaded and compact. The four short sentences each carry distinct information: scope, format, quota, and bulk alternative. No filler.

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

Completeness4/5

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

Given 15 parameters, nested brand object, two enums, and no output schema, the description covers the key operational context well: single-recipient sending, body format, quota, and bulk routing. It is not exhaustive on per-parameter behavior, but the schema supplies substantial detail and annotations cover safety.

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

Parameters3/5

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

Schema description coverage is moderate at 73%, so many parameters are already documented in the schema. The description adds some integrated meaning around text/html bodies and marketing category behavior, but it does not cover most of the 15 parameters, including brand, from, reply_to, template, and button fields.

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: 'Send one email to one recipient.' It also clearly distinguishes transactional vs marketing use and explicitly separates itself from the bulk sibling send_campaign.

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?

Names the bulk alternative explicitly and gives the selecting condition: 'Many recipients at once: send_campaign.' It also indicates the transactional/marketing distinction and the single-recipient scope.

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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