pg_trigram_similarity
Find similar strings using pg_trgm trigram matching. Returns similarity score (0-1). Default threshold 0.3; use lower (e.g., 0.1) for partial matches.
This record as markdown: /tools/io-github-neverinfamous-postgres-mcp/pg-trigram-similarity.md
What pg_trigram_similarity does on PostgreSQL MCP Server
AI agents call pg_trigram_similarity to retrieve information from PostgreSQL MCP Server without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Why pg_trigram_similarity is rated Low
This tool retrieves data (string similarity results) without side effects. It does not create, modify, delete data, execute arbitrary code, or trigger external operations. The threshold parameter controls matching sensitivity but does not alter underlying data. This is a classic Read operation — search/filter over existing content.
From the tool's definition Tool description states it 'Find[s] similar strings' and 'Returns similarity score' — purely a query operation with no modification, deletion, or execution of external commands. The pg_trgm trigram matching is a built-in PostgreSQL text search function.
Attacks that exploit this kind of access
The rule that runs pg_trigram_similarity safely
PolicyLayer is an MCP gateway: it sits between your AI agents and PostgreSQL MCP Server, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For pg_trigram_similarity, this is the rule to start with:
pg_trigram_similarity 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 PostgreSQL MCP Server, apply this rule, and every pg_trigram_similarity call is checked against it from then on.
Questions about pg_trigram_similarity
Find similar strings using pg_trgm trigram matching. Returns similarity score (0-1). Default threshold 0.3; use lower (e.g., 0.1) for partial matches. It is categorised as a Read tool in the PostgreSQL MCP Server MCP Server, which means it retrieves data without modifying state.
Register the PostgreSQL MCP Server MCP server in PolicyLayer and add a rule for pg_trigram_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 PostgreSQL MCP Server. Nothing to install.
pg_trigram_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 pg_trigram_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 pg_trigram_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.
pg_trigram_similarity is provided by the PostgreSQL MCP Server MCP server (@neverinfamous/postgres-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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