Replace an existing observation with new content. Finds the old observation by exact content match and replaces it.
AI agents use update to create or update resources in Hippocampus — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Hippocampus environment.
The tool modifies existing data (observations in the knowledge graph) by replacing content. This is a Write operation because it creates or modifies data reversibly—the old content can theoretically be retrieved or the operation undone through another update. It does not execute external code, delete data irreversibly, or move money.
From the tool's definition Tool description states 'Replace an existing observation with new content', which is a reversible modification operation. The exact phrase 'Replace' indicates data modification rather than deletion or execution of external operations.
Documented attack patterns abuse exactly the kind of access update gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Hippocampus, and nothing reaches the server without passing your rules. This is the rule we recommend for update:
{
"version": "1",
"default": "deny",
"tools": {
"update": {
"limits": [
{
"counter": "update_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update 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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Replace an existing observation with new content. Finds the old observation by exact content match and replaces it. It is categorised as a Write tool in the Hippocampus MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Hippocampus MCP server in PolicyLayer and add a rule for update: 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 Hippocampus. Nothing to install.
update 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 update 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 update. 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.
update is provided by the Hippocampus MCP server (karrolcia/hippocampus). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Hippocampus, 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.
11 Hippocampus tools catalogued and risk-classified — across an index of 43,000+ MCP servers.