Upload a small file (base64, <1MB) or get an HTTP upload URL for larger files. When project_id is set, the upload is gated on write_files capability and the s3 key is scoped under the project
AI agents use crow_upload_file to create or update resources in Crow — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Crow environment.
This tool creates or modifies files in storage (S3), which is a Write operation. It is not Destructive because uploads are reversible (files can be re-uploaded or deleted separately). Severity is medium because while file uploads can be misused (e.g., storing malicious content), the 1MB size limit and project-scoping mitigate the impact. It does not execute code, move funds, or irreversibly delete data.
From the tool's definition Tool description states 'Upload a small file' and 'get an HTTP upload URL for larger files', indicating file creation/modification. Access is 'gated on write_files capability', confirming it modifies data.
Documented attack patterns abuse exactly the kind of access crow_upload_file gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Crow, and nothing reaches the server without passing your rules. This is the rule we recommend for crow_upload_file:
{
"version": "1",
"default": "deny",
"tools": {
"crow_upload_file": {
"limits": [
{
"counter": "crow_upload_file_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}crow_upload_file 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.
Free to start. No card required.
Upload a small file (base64, <1MB) or get an HTTP upload URL for larger files. When project_id is set, the upload is gated on write_files capability and the s3 key is scoped under the project. It is categorised as a Write tool in the Crow MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Crow MCP server in PolicyLayer and add a rule for crow_upload_file: 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 Crow. Nothing to install.
crow_upload_file 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 crow_upload_file 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 crow_upload_file. 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.
crow_upload_file is provided by the Crow MCP server (kh0pper/crow). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Crow, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
576 Crow tools catalogued and risk-classified — across an index of 43,000+ MCP servers.