This record as markdown: /tools/io-github-kivanccakmak-yaver/storage-presign.md
What storage_presign does on Yaver
AI agents call storage_presign to retrieve information from Yaver without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
| Parameter | Type | Required | Description |
|---|---|---|---|
key | string | Yes | |
bucket | string | Yes | |
expiry | string | — | Expiry duration (e.g. 1h, 24h) |
Parameters from the server's own tool schema.
Why storage_presign is rated Low
Presigned URLs are a standard mechanism to grant temporary, read-only access to cloud storage objects. This is fundamentally a Read operation—it retrieves metadata (a URL) that permits access to data, but does not modify, delete, execute code, or transfer funds.
From the tool's definition The tool generates a presigned URL for an S3 object, allowing temporary access to retrieve objects. The description explicitly states it generates URLs for access, which is a read-only operation that retrieves or queries data without modification.
Attacks that exploit this kind of access
The rule that runs storage_presign safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Yaver, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For storage_presign, this is the rule to start with:
storage_presign is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Yaver, apply this rule, and every storage_presign call is checked against it from then on.
Questions about storage_presign
Generate a presigned URL for an S3 object. It is categorised as a Read tool in the Yaver MCP Server, which means it retrieves data without modifying state.
storage_presign accepts 3 parameters: key, bucket, expiry. Required: key, bucket. The full parameter table on this page comes from the server's own tool schema.
Register the Yaver MCP server in PolicyLayer and add a rule for storage_presign: 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 Yaver. Nothing to install.
storage_presign is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the storage_presign 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 storage_presign. 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.
storage_presign is provided by the Yaver MCP server (yaver-cli). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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