pg_jsonb_insert
Insert value into JSONB array or object. For arrays, index -1 inserts BEFORE last element (use insertAfter:true to append). For objects, throws error if key already exists.
This record as markdown: /tools/io-github-neverinfamous-postgres-mcp/pg-jsonb-insert.md
What pg_jsonb_insert does on PostgreSQL MCP Server
AI agents use pg_jsonb_insert to create or update resources in PostgreSQL MCP Server, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your PostgreSQL MCP Server environment.
Why pg_jsonb_insert is rated Medium
This tool creates or modifies data reversibly by inserting values into JSONB columns. It does not execute arbitrary code, delete data irreversibly, move money, or trigger external operations—it performs a standard database write operation that can be undone (via UPDATE or DELETE). The 'throws error if key already exists' behavior indicates write-level semantics rather than destructive operations.
From the tool's definition Tool name contains 'insert' and description states 'Insert value into JSONB array or object', which modifies data within the database by adding new values to existing JSONB structures.
Attacks that exploit this kind of access
The rule that runs pg_jsonb_insert 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_jsonb_insert, this is the rule to start with:
pg_jsonb_insert 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.
The button opens the PolicyLayer dashboard: create your workspace, connect PostgreSQL MCP Server, apply this rule, and every pg_jsonb_insert call is checked against it from then on.
Questions about pg_jsonb_insert
Insert value into JSONB array or object. For arrays, index -1 inserts BEFORE last element (use insertAfter:true to append). For objects, throws error if key already exists. It is categorised as a Write tool in the PostgreSQL MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the PostgreSQL MCP Server MCP server in PolicyLayer and add a rule for pg_jsonb_insert: 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_jsonb_insert 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 pg_jsonb_insert 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_jsonb_insert. 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_jsonb_insert 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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