AI agents use replace_value 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 existing data values within files through AST-based editing. It is reversible (the original value can be restored by replacing it back), distinguishing it from Destructive operations. The high severity reflects that malicious value replacement in code could introduce logic bugs, security vulnerabilities, or data corruption, though the impact remains bounded by the ability to reverse the change.
From the tool's definition Tool name 'replace_value' combined with server description stating it provides 'AI coding agents with the ability to edit files surgically via Abstract Syntax Trees' indicates modification of code/data.
Documented attack patterns abuse exactly the kind of access replace_value 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_value:
{
"version": "1",
"default": "deny",
"tools": {
"replace_value": {
"limits": [
{
"counter": "replace_value_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}replace_value 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_value. 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_value: 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_value 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_value 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_value. 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_value 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.