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MCPg - Production-grade PostgreSQL MCP Server

MCPg - Production-grade PostgreSQL MCP Server

by devopam
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

Describe Redis cache table

describe_redis_cache_table
Read-only

Inspect a Redis-backed foreign table to reveal its server mapping, key type, key prefix, TTL, and SQL column shape before querying or debugging it.

Instructions

Describe one foreign table backed by redis_fdw: which server it's mapped to, the Redis-side key structure (hash / list / string / set / zset), key-prefix, TTL, and SQL-side column shape. Raises an error when the table doesn't exist or isn't backed by redis_fdw. Returns an object with schema, name, server, key_type, key_prefix, ttl_seconds, columns (list of {name, data_type}), and options (the full foreign-table options dict).

Example: describe_redis_cache_table(schema='public', table='sessions_cache')

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": "describe_redis_cache_table"
  }
}

Input Schema

NameRequiredDescriptionDefault
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
nameYes
schemaYes
serverYes
columnsYes
optionsYes
key_typeYes
key_prefixYes
ttl_secondsYes

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

A3.9/5.0
Behavior4/5

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds meaningful behavior beyond that: it discloses the error behavior for missing/non-redis tables and enumerates the returned fields, which annotations cannot convey.

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 text is front-loaded with purpose, then behavior, then return shape, then a compact example — a sensible structure. It is somewhat dense with return-field enumeration, but each clause carries information 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?

An output schema exists, so the return-field listing is partially redundant, but for a describe-style tool the extra specificity is harmless. Combined with the error behavior and the example, an agent has enough to invoke it correctly; the only gap is guidance on when to prefer this over describe_table or list_foreign_tables.

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 description coverage is only 33% — only the optional `database` parameter is documented (and that is documented in the schema, not the description). The description's example call clarifies the required `schema` and `table` as identifier arguments, but adds no semantics for the primary/secondary database targeting beyond what the schema already states.

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

Purpose5/5

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 ('Describe one foreign table backed by redis_fdw') and immediately enumerates what is disclosed (server mapping, Redis key type, prefix, TTL, SQL column shape). This distinguishes it clearly from sibling tools like describe_table or list_foreign_tables, which are generic rather than redis_fdw-specific.

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 implied by the redis_fdw scoping and the error condition ('raises an error when the table doesn't exist or isn't backed by redis_fdw'), which implicitly routes agents with ordinary tables to describe_table. However, no sibling is named explicitly and there is no explicit 'use this instead of X when Y' guidance.

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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