sendmux-attachments SKILL.md skillA
sendmux-attachments from sendmux/skills is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add sendmux/skills/sendmux-attachments@v1.0Pins v1.0 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- sendmux/skills
- Path
plugins/sendmux/skills/sendmux-attachments/SKILL.md- Versions recorded
- 4
- Latest version
- v1.0, committed Sep 30, 2026
- First version recorded
- Jul 9, 2026
- Size
- 13,367 bytes
- Repository stars
- 18
- License
- a license file GitHub does not identify
Use Sendmux attachment workflows without wasting model context on base64. Use when uploading, downloading, reading, forwarding, or sending email attachments through Sendmux MCP, CLI, SDKs, or direct HTTP, especially when choosing file_path vs presigned upload URL vs inline base64, reading inbound attachments with mailbox_read_attachment, fetching short-lived download_url links, or attaching local files to outbound mail.
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# Sendmux attachments Use this skill whenever a Sendmux task involves attachment bytes. ## Core rule Do not pipe real files through model context as base64. MCP uses bounded inline content for tiny agent-authored files or a signed URL for external byte transfer; CLI and SDK file helpers may read local paths. | Mode | Use when | Token cost | Limit | | --- | --- | ---: | --- | | MCP presigned upload | A local or hosted MCP agent has a real file and an external byte-transfer surface. | tiny | Mailbox: 7,500,000 bytes. Sending: the upload intent's returned `max_size_bytes`. | | CLI `--attach` / SDK file helpers | Terminal or application code can read the local file. | tiny | Obey the selected Mailbox or Sending surface's current bound. | | MCP inline base64 | Content is tiny and agent-authored. | high | 32,768 decoded bytes, not encoded-text length. | Approximate base64 cost: 25 KB becomes about 11K generated tokens; 1 MB is impractical. A file path is usually under 100 tokens. ## Security model …
Read the whole file at its exact version.
How to install
mdr add sendmux/skills/sendmux-attachments@sha256:bf4b381efd3e89afThe line at the top of this page pins the label v1.0, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_26ldmpeygzbr3xhp)
4 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 4 versions of this file, between Jul 9, 2026 and Sep 30, 2026, about one every 28 days.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| v1.0 latest | 2026-09-30 | 39b98e9 | 13,367 B | A | view · diff |
| v1.0 | 2026-09-15 | 3de00a3 | 13,133 B | A | view · diff |
| v1.0 | 2026-08-31 | e2834ee | 10,240 B | A | view · diff |
| v1.0 | 2026-07-09 | 6c471fe | 9,871 B | A | view |
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (13367 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
sendmux/skills · 18 stars · license a license file GitHub does not identify · pushed 2026-10-15 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_26ldmpeygzbr3xhp GET https://markdownregistry.com/api/v1/resolve?ref=sendmux/skills/sendmux-attachments GET https://markdownregistry.com/api/v1/blob/bf4b381efd3e89afef46464c0b68b948bfd3bc8eb69a6d3993fad8ae3dca77e2
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.