AI agents use replace_cell_source to create or update resources in Ast Editor — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Ast Editor environment.
This tool modifies code by replacing cell source content, which is a Write operation (reversible modification). While it could theoretically enable destructive patterns if combined with other operations, the isolated action is modification rather than deletion.
From the tool's definition Tool name 'replace_cell_source' indicates modification of cell source code. Server description emphasizes 'edit files surgically via Abstract Syntax Trees' and the sibling tools (add_cell, add_method, add_import, etc.) all perform reversible code…
Documented attack patterns abuse exactly the kind of access replace_cell_source gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Ast Editor, and nothing reaches the server without passing your rules. This is the rule we recommend for replace_cell_source:
{
"version": "1",
"default": "deny",
"tools": {
"replace_cell_source": {
"limits": [
{
"counter": "replace_cell_source_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}replace_cell_source 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_cell_source. It is categorised as a Write tool in the Ast Editor MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Ast Editor MCP server in PolicyLayer and add a rule for replace_cell_source: 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 Ast Editor. Nothing to install.
replace_cell_source 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 replace_cell_source 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 replace_cell_source. 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.
replace_cell_source is provided by the Ast Editor MCP server (kambleakash0/agent-skills). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Ast Editor, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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59 Ast Editor tools catalogued and risk-classified — across an index of 43,000+ MCP servers.