Set the bit at offset to value. Args: key: The name of the bitmap key offset: The bit offset (0-based) value: The bit value (0 or 1) Returns: Success message or error message
AI agents use bitmap_set to create or update resources in AWS — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your AWS environment.
This tool modifies data (sets a bit to 0 or 1) in a reversible manner—the bit can be flipped back to its previous state. It does not delete data irreversibly, execute arbitrary code, move money, or query for reads only. The blast radius is limited to the specific bitmap key and bit offset provided. Categorized as Write rather than Read (which would be bitmap_get) or Execute (no code execution or external triggers).
From the tool's definition Tool description explicitly states it "Set[s] the bit at offset to value," modifying data by changing a bit in a bitmap key. The return type indicates success or error, confirming a state-changing operation.
Documented attack patterns abuse exactly the kind of access bitmap_set gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and AWS, and nothing reaches the server without passing your rules. This is the rule we recommend for bitmap_set:
{
"version": "1",
"default": "deny",
"tools": {
"bitmap_set": {
"limits": [
{
"counter": "bitmap_set_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}bitmap_set 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.
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Set the bit at offset to value. Args: key: The name of the bitmap key offset: The bit offset (0-based) value: The bit value (0 or 1) Returns: Success message or error message. It is categorised as a Write tool in the AWS MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the AWS MCP server in PolicyLayer and add a rule for bitmap_set: 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 AWS. Nothing to install.
bitmap_set 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 bitmap_set 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 bitmap_set. 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.
bitmap_set is provided by the AWS MCP server (@awslabs/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from AWS, 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.
300 AWS tools catalogued and risk-classified — across an index of 43,000+ MCP servers.