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MCPg - Production-grade PostgreSQL MCP Server

MCPg - Production-grade PostgreSQL MCP Server

by devopam
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

List indexes

list_indexes
Read-only

List indexes defined on a PostgreSQL table, returning name, method, definition, and partitioned status. Bypass the cache with fresh=true after schema changes.

Instructions

List the indexes defined on a table. Set fresh=true to bypass the cache and re-read live (e.g. after a schema change). Returns a list of objects with name, method (btree / gin / gist / brin / hash / spgist / hnsw / ivfflat / …), definition (the CREATE INDEX statement), and partitioned.

Example: list_indexes(schema='public', table='users')

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "schema": "<schema>",
      "table": "<table>"
    },
    "name": "list_indexes"
  }
}

Input Schema

NameRequiredDescriptionDefault
freshNo
tableYes
schemaYes
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. Changed1 schema field changed
    • addedInput schema / properties / fresh
      Added value: +{
+  "default": false,
+  "title": "Fresh",
+  "type": "boolean"
+}
  3. First observedv0.6.8

TDQS

A3.8/5.0
Behavior4/5

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

The annotations only declare readOnlyHint and openWorldHint, but the description adds a real behavioral detail they do not carry: results are cached, and fresh=true forces a live re-read after DDL. It also pre-empts confusion over stale results, which matters for a schema-introspection tool. It does not mention cost or latency of a fresh read, and the return shape is already implied by the output schema, so a 4 rather than a 5.

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?

The structure is front-loaded: purpose first, then the cache escape hatch, then the return shape, then an example. Every sentence carries information. The return-field enumeration runs slightly long given that an output schema exists, but it is still useful as a quick reference.

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?

This is a simple read tool with an output schema that needs no return-value explanation, and the description still covers cache semantics, invalidation trigger, return fields, and a call example. The only real gap is the absence of any disambiguation from the vector and pg_search index siblings.

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

Parameters4/5

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

Schema coverage is 25%: only database is documented there, and it is documented well. The description compensates by explaining what fresh actually does and by showing schema and table in a worked example. It never mentions the optional database parameter or the read-only secondary-database targeting, but the schema covers that.

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 definition opens with a concrete verb plus resource and scope: "List the indexes defined on a table." That separates it from siblings such as recommend_indexes or list_constraints. It stops short of naming the nearest overlapping siblings (list_pg_search_indexes, get_turboquant_index_metadata, list_turboquant_indexes), so the boundary still takes some inference.

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 guidance is limited to one concrete case: set fresh=true to bypass the cache and re-read live, e.g. after a schema change. The description never says when to reach for this tool instead of list_pg_search_indexes or the turboquant index inspectors, and it states no prerequisites such as permissions on the target schema.

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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