Proton Suite Agent

Download an attachment

proton_get_attachment

Read-onlyIdempotent

Returns the base64-encoded bytes of a specific email attachment by its index. Supports truncation of large attachments with a maximum size limit.

Instructions

Returns the bytes of a specific attachment encoded as base64. Use the attachment index from proton_get_email. Large attachments are truncated to max_bytes (default 10 MB) with a truncated=true flag in the response.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "uid": "<uid>",
      "index": "<index>"
    },
    "name": "proton_get_attachment"
  }
}

Input Schema

Name	Required	Description	Default
`uid`	Yes
`index`	Yes	Zero-based index in the attachments array
`mailbox`	No		INBOX
`max_bytes`	No	Maximum attachment size in bytes (default 10 MB, hard cap 50 MB)

Output Schema

Name	Required	Description	Default
`base64`	Yes
`filename`	No
`truncated`	Yes
`size_bytes`	Yes
`contentType`	Yes
`returned_bytes`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.8.0Jul 28, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations provide readOnlyHint, openWorldHint, idempotentHint. The description adds that large attachments are truncated to max_bytes with a truncated=true flag, which is useful behavioral context beyond 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?

Two short, dense sentences; front-loaded with core purpose; no redundant information. Every word earns its place.

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 an output schema present, the description need not explain return values. It covers key behaviors (base64 encoding, truncation) and prerequisites. Lacks only edge-case details, which is acceptable.

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 50%. The description adds meaning for max_bytes (default 10 MB, hard cap 50 MB) and references index from get_email, but does not elaborate on uid or mailbox beyond schema. Adequate but not exceptional.

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?

The description clearly states it returns base64-encoded bytes of a specific attachment, using the attachment index from proton_get_email. It distinctly differentiates from sibling tools like proton_drive_download.

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

Usage Guidelines4/5

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

The description tells when to use it (to get attachment bytes) and mentions the prerequisite of using proton_get_email. It doesn't explicitly say when not to use it or list alternatives, which lowers to 4.

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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