save_attachment
Use only when the user specifies a destination path; prefer receive_attachment for automatic receiving. Downloads an attachment addressed to the current member and verifies SHA-256 before publishing the saved file. Omit path for backward-compatible package-root downloads/ (not cwd), created only ...
This record as markdown: /tools/a2a-msg/save-attachment.md
What save_attachment does on A2a Msg
AI agents use save_attachment to create or update resources in A2a Msg, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your A2a Msg environment.
Why save_attachment is rated Medium
An AI agent can call save_attachment faster than any human can review: one bad instruction and it creates or modifies resources in A2a Msg by the hundred, each call as confident as the last.
Risk signalsAdmin/system-level operation
Attacks that exploit this kind of access
The rule that runs save_attachment safely
PolicyLayer is an MCP gateway: it sits between your AI agents and A2a Msg, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For save_attachment, this is the rule to start with:
save_attachment stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect A2a Msg, apply this rule, and every save_attachment call is checked against it from then on.
Questions about save_attachment
Use only when the user specifies a destination path; prefer receive_attachment for automatic receiving. Downloads an attachment addressed to the current member and verifies SHA-256 before publishing the saved file. Omit path for backward-compatible package-root downloads/ (not cwd), created only when saving; optional MSG_DOWNLOAD_DIR overrides it with an existing absolute directory. Omission forces auto_name=true and overwrite=false. Explicit path keeps existing semantics. Traceable names use exclusive publication and bounded retries. Saving does not mark read; save successfully before reading the body, or ask to retry, skip or cancel on failure. ${READING_GUIDANCE} ${UNTRUSTED}. It is categorised as a Write tool in the A2a Msg MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the A2a Msg MCP server in PolicyLayer and add a rule for save_attachment: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches A2a Msg. Nothing to install.
save_attachment is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the save_attachment rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for save_attachment. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
save_attachment is provided by the A2a Msg MCP server (goudaren0528/a2a-msg). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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