hash_exists
Check if field exists in hash. Args: key: The name of the key field: The field name Returns: Boolean result or error message
This record as markdown: /tools/aws/hash-exists.md
What hash_exists does on AWS
AI agents call hash_exists to retrieve information from AWS without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Why hash_exists is rated Low
This tool performs a simple existence check on a hash field, which is a read-only operation with no side effects. It queries state but does not create, modify, delete, or execute any operations. The blast radius of misuse is minimal—an agent could only learn whether a field exists in a hash structure.
From the tool's definition Tool description states 'Check if field exists in hash' with return type 'Boolean result or error message'. This is a query operation that retrieves existence information without modifying data.
Attacks that exploit this kind of access
The rule that runs hash_exists safely
PolicyLayer is an MCP gateway: it sits between your AI agents and AWS, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For hash_exists, this is the rule to start with:
hash_exists 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 AWS, apply this rule, and every hash_exists call is checked against it from then on.
Questions about hash_exists
Check if field exists in hash. Args: key: The name of the key field: The field name Returns: Boolean result or error message. It is categorised as a Read tool in the AWS MCP Server, which means it retrieves data without modifying state.
Register the AWS MCP server in PolicyLayer and add a rule for hash_exists: 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.
hash_exists 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 hash_exists 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 hash_exists. 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.
hash_exists 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.
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