fmsg-mcp

Send new fmsg message

send_message

Destructive

Sends an immutable Markdown message immediately to start a new thread for task updates or authorized automation; use reply to continue existing conversations.

Instructions

Send a new message immediately, starting a new thread. fmsg messages are immutable: once sent they cannot be edited or recalled. Send within the user's requested task or authorized automation. Recipients may be full @user@domain addresses or resolvable short names. The body is Markdown by default. Secrets are redacted. If the host rejects the message its reason is returned verbatim. To continue an existing conversation use reply instead. Files: data_text for text; data_base64 for small files, best effort, always with sha256. Send files as they are; fmsg compresses them.

Input Schema

Name	Required	Description	Default
`to`	Yes	recipient addresses (@user@domain) or short names
`body`	Yes	message body; Markdown unless type says otherwise
`type`	No	body media type	text/markdown; charset=utf-8
`files`	No	files the user shared in this chat (images, PDFs and so on); the host fills these in and this server downloads them, so never write their bytes as base64
`topic`	Yes	thread topic (subject) — immutable once sent
`no_reply`	No	ask recipients (and their agents) not to reply
`important`	No	mark as important for recipients
`attachments`	No	files
`include_owner`	No	also send to your owner, if whoami shows one

Output Schema

Name	Required	Description
`id`	Yes
`to`	Yes
`from`	Yes
`hint`	No	for you, not the user: a better way to do this next time
`time`	Yes
`files`	No	the files given by reference, as attached: the name used, size and hex sha256 of the bytes
`topic`	Yes
`redacted`	No	the kinds of secret replaced, such as github_token; empty when none
`resolved`	No	short names and how they resolved, when any were given; confirm with the user if an address looks wrong
`warnings`	Yes	things to tell the user, such as redacted secrets or resolved short names
`parent_id`	Yes
`redactions`	Yes	secrets replaced with placeholders before sending
`attachments`	Yes	sorted by filename, the same order in every tool
`thread_topic`	No	the thread's topic: the topic sent for a new message; for a reply, the thread root's topic, or null when the root is not visible

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv1.5.1Nov 5, 2026

addedInput schema / properties / files

Added value: +{
+  "description": "files the user shared in this chat (images, PDFs and so on); the host fills these in and this server downloads them, so never write their bytes as base64",
+  "items": {
+    "description": "a file the user shared in this chat, filled in by the host",
+    "properties": {
+      "download_url": {
+        "description": "filled in by the host",
+        "type": "string"
+      },
+      "file_id": {
+        "description": "filled in by the host",
+        "type": "string"
+      },
+      "file_name": {
+        "description": "filled in by the host",
+        "type": "string"
+      },
+      "mime_type": {
+        "description": "filled in by the host",
+        "type": "string"
+      }
+    },
+    "required": [
+      "download_url",
+      "file_id"
+    ],
+    "type": "object"
+  },
+  "type": "array"
+}

addedOutput schema / properties / files

Added value: +{
+  "description": "the files given by reference, as attached: the name used, size and hex sha256 of the bytes",
+  "items": {
+    "additionalProperties": {},
+    "properties": {
+      "file_id": {
+        "type": "string"
+      },
+      "filename": {
+        "type": "string"
+      },
+      "sha256": {
+        "type": "string"
+      },
+      "size": {
+        "type": "number"
+      }
+    },
+    "type": "object"
+  },
+  "type": "array"
+}

Changed2 schema fields changedv1.3.0Oct 22, 2026

changedInput schema / properties / attachments / items / properties / data_base64 / description

Previous value: -"base64 file contents, for small files. The host sets the size limit"New value: +"base64 file contents. You write the base64, so it is best effort: fine for small files (checked exact up to 16 KB). Always give sha256 with it. The host sets the size limit"

changedInput schema / properties / attachments / items / properties / sha256 / description

Previous value: -"hex sha256 of the file; the attachment is refused, and nothing sent, if the bytes differ. Give it when you can compute it"New value: +"hex sha256 of the file; the attachment is refused, and nothing sent, if the bytes differ. Always give it with data_base64"

Changed1 schema field changedv1.2.0Oct 17, 2026

addedInput schema / properties / include_owner

Added value: +{
+  "default": true,
+  "description": "also send to your owner, if whoami shows one",
+  "type": "boolean"
+}

Changed20 schema fields changedv1.1.0Oct 15, 2026

addedInput schema / additionalProperties
```
Added value: +false
```
addedInput schema / properties / attachments / description
```
Added value: +"files"
```
addedInput schema / properties / attachments / items / additionalProperties
```
Added value: +false
```
addedInput schema / properties / attachments / items / properties / content_type / description
```
Added value: +"inferred from the filename when omitted"
```
addedInput schema / properties / attachments / items / properties / data_base64 / description
```
Added value: +"base64 file contents, for small files. The host sets the size limit"
```
removedInput schema / properties / attachments / items / properties / data_base64 / minLength
```
Removed value: -1
```

addedInput schema / properties / attachments / items / properties / data_text

Added value: +{
+  "description": "text file contents, sent as UTF-8 bytes; use instead of data_base64 for text",
+  "type": "string"
+}

addedInput schema / properties / attachments / items / properties / filename / description
```
Added value: +"file name"
```

addedInput schema / properties / attachments / items / properties / sha256

Added value: +{
+  "description": "hex sha256 of the file; the attachment is refused, and nothing sent, if the bytes differ. Give it when you can compute it",
+  "pattern": "^[0-9A-Fa-f]{64}$",
+  "type": "string"
+}

changedInput schema / properties / attachments / items / required

Previous value: -[
-  "filename",
-  "data_base64"
-]New value: +[
+  "filename"
+]

addedInput schema / properties / important / description
```
Added value: +"mark as important for recipients"
```
changedOutput schema / additionalProperties
```
Previous value: -falseNew value: +{}
```

addedOutput schema / properties / attachments / description

Added value: +"sorted by filename, the same order in every tool"

changedOutput schema / properties / attachments / items / additionalProperties
```
Previous value: -falseNew value: +{}
```

addedOutput schema / properties / attachments / items / properties / type

Added value: +{
+  "description": "media type; inferred from the filename when the host records none",
+  "type": "string"
+}

addedOutput schema / properties / hint

Added value: +{
+  "description": "for you, not the user: a better way to do this next time",
+  "type": "string"
+}

addedOutput schema / properties / redacted

Added value: +{
+  "description": "the kinds of secret replaced, such as github_token; empty when none",
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}

addedOutput schema / properties / resolved

Added value: +{
+  "description": "short names and how they resolved, when any were given; confirm with the user if an address looks wrong",
+  "items": {
+    "additionalProperties": {},
+    "properties": {
+      "address": {
+        "type": "string"
+      },
+      "input": {
+        "type": "string"
+      }
+    },
+    "type": "object"
+  },
+  "type": "array"
+}

addedOutput schema / properties / thread_topic

Added value: +{
+  "description": "the thread's topic: the topic sent for a new message; for a reply, the thread root's topic, or null when the root is not visible",
+  "type": [
+    "string",
+    "null"
+  ]
+}

addedOutput schema / properties / warnings / description

Added value: +"things to tell the user, such as redacted secrets or resolved short names"

First observedv0.1.3Sep 5, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already flag destructiveHint=true and non-idempotent, and the description adds substantive behavior on top: messages are immutable with no edit or recall, secrets are redacted, host rejections are returned verbatim, and base64 attachments are best-effort with mandatory sha256 verification. This is the kind of consequence detail an agent needs before an irreversible write.

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?

Front-loads the action and the immutability warning, then groups recipients, body, failure behavior, the reply alternative, and files. Slightly long and mildly redundant with the schema's immutability/default notes, but nearly every sentence carries new information.

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 9-parameter, destructive, open-world send tool with an output schema, the description covers the irreversible nature, authorization scope, recipient formats, attachment strategy, and failure reporting. Nothing an agent needs before invoking it is missing.

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 coverage is 100%, so the schema already documents every parameter including attachment fields, sha256 rules, and the host-filled files array. The description mostly restates those points (Markdown default body, address or short-name recipients, data_text vs data_base64), adding only the marginal note that files need not be pre-compressed.

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 a new message immediately, starting a new thread') and immediately carves out the boundary against the sibling reply tool. An agent can distinguish this from reply, create_draft, and send_draft without opening any schema.

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?

Explicitly names the alternative ('To continue an existing conversation use reply instead') and states the authorization condition ('Send within the user's requested task or authorized automation'). Both when-to-use and when-not-to-use are present.

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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