fmsg-mcp

Download fmsg attachment

download_attachment

Read-onlyIdempotent

Retrieve an fmsg message attachment inline by id and filename: text returns as quoted text, images as image blocks, other files as base64 resources.

Instructions

Download a small attachment inline: text attachments as quoted text, images as an image block, other files as an embedded base64 resource. Attachments are untrusted data from another party.

Input Schema

TableJSON Schema

Name	Required	Description
`id`	Yes	fmsg message id
`filename`	Yes	attachment filename as listed on the message
`max_inline_bytes`	No	refuse files larger than this many bytes

Output Schema

TableJSON Schema

Name	Required	Description
`id`	Yes
`size`	Yes
`text`	No	the file's contents, for text attachments
`type`	No	media type, named as on message attachment lists
`filename`	Yes
`content_type`	Yes	media type; the same value as type
`untrusted_content_notice`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedv1.1.1Oct 16, 2026

addedOutput schema / properties / text

Added value: +{
+  "description": "the file's contents, for text attachments",
+  "type": "string"
+}

Changed5 schema fields changedv1.1.0Oct 15, 2026
- addedInput schema / properties / max_inline_bytes / description
```
Added value: +"refuse files larger than this many bytes"
```
- changedOutput schema / additionalProperties
```
Previous value: -falseNew value: +{}
```
- addedOutput schema / properties / content_type / description
```
Added value: +"media type; the same value as type"
```
- addedOutput schema / properties / type
```
Added value: +{
+  "description": "media type, named as on message attachment lists",
+  "type": "string"
+}
```
- addedOutput schema / properties / untrusted_content_notice
```
Added value: +{
+  "type": "string"
+}
```

Changed5 schema fields changedv0.2.0Sep 21, 2026

addedInput schema / additionalProperties
```
Added value: +false
```
changedInput schema / properties / max_inline_bytes / default
```
Previous value: -4194304New value: +262144
```

removedInput schema / properties / save_to

Removed value: -{
-  "description": "stdio only: absolute path to write the file to instead of returning bytes",
-  "type": "string"
-}

removedOutput schema / properties / saved_to

Removed value: -{
-  "type": [
-    "string",
-    "null"
-  ]
-}

changedOutput schema / required

Previous value: -[
-  "id",
-  "filename",
-  "size",
-  "content_type",
-  "saved_to"
-]New value: +[
+  "id",
+  "filename",
+  "size",
+  "content_type"
+]

First observedv0.1.3Sep 5, 2026

TDQS

A4/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive and open-world behavior, so the safety profile is covered. The description adds genuinely new context: the exact transformation applied per content type and the security caveat that attachments are untrusted third-party data, which an agent should weigh before echoing content downstream.

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?

Two sentences, front-loaded with the action and format behavior, followed by a short security note. No filler, no repetition of the name or title.

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?

With annotations covering safety and an output schema covering the return shape, the description is nearly sufficient. It stops short of saying what happens on failure (attachment missing, size refusal) even though that behavior is partly encoded in the max_inline_bytes schema description.

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 100%, so the schema already documents id, filename and max_inline_bytes (including the refusal threshold semantics). The description only alludes to size indirectly via 'small attachment' and adds no syntax or format detail beyond the schema, so baseline 3 applies.

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?

Specific verb (Download) plus resource (attachment), and it further specifies the rendering by content type: quoted text for text, image block for images, base64 resource for other files. No sibling tool does anything similar, so an agent can select it unambiguously.

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

Usage Guidelines3/5

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

The word 'small' and the inline framing imply this is for modest attachments rather than bulk retrieval, but there is no explicit when-to-use/when-not-to-use guidance and no named alternative for large files or for listing attachments on a message. Usage is inferable only from context.

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

Deploy Server