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MCPg - Production-grade PostgreSQL MCP Server

MCPg - Production-grade PostgreSQL MCP Server

by devopam
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

List active queries

list_active_queries
Read-only

Identify currently running PostgreSQL queries, their wait events, durations, and blocking PIDs to diagnose slow or stuck database activity.

Instructions

List the queries currently running on the server, with each backend's wait event, duration, and the PIDs blocking it. Returns a list of objects with pid, username, application, state, wait_event (null when not waiting), duration_seconds, query, and blocked_by (list of PIDs holding locks this backend is waiting on).

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "list_active_queries"
  }
}

Input Schema

NameRequiredDescriptionDefault
databaseNoOptional: a database id from list_databases, to target a configured secondary (read-only) database; omit for the primary. Database names that are not configured ids are rejected.

Output Schema

NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.8.4
    • changedInput schema / properties / database / description
      Previous value: -"Optional: target a configured secondary (read-only) database by name; omit for the primary. Call list_databases to see the configured ids."New value: +"Optional: a database id from list_databases, to target a configured secondary (read-only) database; omit for the primary. Database names that are not configured ids are rejected."
  2. First observedv0.6.8

TDQS

A3.5/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds useful return-shape semantics ('wait_event' null when not waiting, blocked_by as a list of PIDs), but says nothing about visibility restrictions on pg_stat_activity (non-superusers/roles without pg_read_all_stats only see their own sessions), which materially affects interpretation of results.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the core action, and the field enumeration is compact. The field list is somewhat redundant with the existing output schema, but it reads cleanly and there is no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, the description need not explain return values, and it restates them anyway. For a read-only, single-optional-parameter tool this is nearly complete; the main omissions are permission/visibility caveats and sibling routing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the single 'database' parameter is fully documented in the schema, including the list_databases cross-reference and rejection of unconfigured names. The description adds nothing about the parameter, so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: 'List the queries currently running on the server,' which is unambiguous. It does not explicitly distinguish itself from related siblings like find_blocking_chains, list_locks, or read_pg_stat_lock, even though it reports blocked_by PIDs that overlap with those tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied: an agent can infer this is the live-session monitoring tool from 'currently running.' There is no explicit when-to-use/when-not guidance and no routing to alternatives such as find_blocking_chains for deep lock analysis or why_is_this_slow for a single query diagnosis.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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