Find similar text using trigram similarity (requires pg_trgm extension)
AI agents call text_similarity to retrieve information from Postgres Mcp Legacy without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool searches for similar text using PostgreSQL's trigram similarity feature, which is a read-only operation that returns matching results without side effects. It does not create, modify, delete, execute arbitrary code, or commit financial transactions. The pg_trgm extension requirement confirms it's a standard PostgreSQL text search utility.
From the tool's definition Tool name 'text_similarity' and description 'Find similar text using trigram similarity' indicate a query operation that retrieves or matches data without modifying it.
Documented attack patterns abuse exactly the kind of access text_similarity gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Postgres Mcp Legacy, and nothing reaches the server without passing your rules. This is the rule we recommend for text_similarity:
{
"version": "1",
"default": "deny",
"tools": {
"text_similarity": {}
}
}text_similarity is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Find similar text using trigram similarity (requires pg_trgm extension). It is categorised as a Read tool in the Postgres Mcp Legacy MCP Server, which means it retrieves data without modifying state.
Register the Postgres Mcp Legacy MCP server in PolicyLayer and add a rule for text_similarity: 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 Postgres Mcp Legacy. Nothing to install.
text_similarity 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 text_similarity 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 text_similarity. 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.
text_similarity is provided by the Postgres Mcp Legacy MCP server (neverinfamous/postgres-mcp-legacy). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Postgres Mcp Legacy, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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60 Postgres Mcp Legacy tools catalogued and risk-classified — across an index of 43,000+ MCP servers.