Add a value to the cache only if the key doesn't exist.
AI agents use cache_add to create or update resources in Awslabs Amazon Sns Sqs — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Awslabs Amazon Sns Sqs environment.
cache_add performs a conditional cache insertion, which is a reversible write operation. It has minimal blast radius because it only affects cache entries (typically ephemeral state), does not execute code, delete data, or move money. Severity is low because cache operations have limited downstream impact compared to database or storage mutations.
From the tool's definition Tool description states 'Add a value to the cache' — this is a create/write operation that modifies cache state.
Documented attack patterns abuse exactly the kind of access cache_add gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Awslabs Amazon Sns Sqs, and nothing reaches the server without passing your rules. This is the rule we recommend for cache_add:
{
"version": "1",
"default": "deny",
"tools": {
"cache_add": {
"limits": [
{
"counter": "cache_add_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}cache_add 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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Add a value to the cache only if the key doesn't exist. It is categorised as a Write tool in the Awslabs Amazon Sns Sqs MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Awslabs Amazon Sns Sqs MCP server in PolicyLayer and add a rule for cache_add: 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 Awslabs Amazon Sns Sqs. Nothing to install.
cache_add 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 cache_add 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 cache_add. 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.
cache_add is provided by the Awslabs Amazon Sns Sqs MCP server (awslabs.amazon-sns-sqs-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Awslabs Amazon Sns Sqs, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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