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MCPg - Production-grade PostgreSQL MCP Server

MCPg - Production-grade PostgreSQL MCP Server

by devopam
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

List foreign keys

list_foreign_keys
Read-only

Lists foreign keys in a schema, resolving each constraint to its columns and referenced table so you can map relationships accurately.

Instructions

List foreign keys in a schema, resolved to columns and referenced 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, from_table, from_columns, to_schema, to_table, to_columns.

Example: list_foreign_keys(schema='public')

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>"
    },
    "name": "list_foreign_keys"
  }
}

Input Schema

NameRequiredDescriptionDefault
freshNo
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

A4.1/5.0
Behavior4/5

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

Annotations already declare this a read-only, closed-world operation, so the safety profile is covered. The description adds real behavior the annotations do not: results are cache-backed and a stale read is possible unless fresh=true is set. It does not state what happens on an unknown schema (empty list vs error), leaving one behavioral gap.

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

Conciseness5/5

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

Two compact sentences plus a one-line example: the core action leads, the cache escape hatch follows, and the return shape is a single clause. Nothing is redundant and nothing is buried.

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 does not need to enumerate return fields, yet it names them anyway, and it covers the cache dimension that is otherwise invisible. What remains unaddressed is behavior on an invalid or missing schema and any mention that this overlaps with list_constraints.

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 description coverage is only 33%, so the description has to compensate, and it does for two of three params: fresh is explained with its purpose and trigger, and schema is demonstrated via the worked example. The database parameter is fully documented in the schema itself, so its absence from the description is no loss.

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?

States a specific verb and resource ('List foreign keys in a schema') plus what the output resolves to (columns and referenced table), which lets an agent distinguish this from generic tools like list_tables. It stops short of naming the closest sibling, list_constraints, which also surfaces FK constraints, so the boundary is not fully explicit.

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

Usage Guidelines4/5

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

Gives a concrete invocation example and a clear condition for the non-default parameter ('set fresh=true ... e.g. after a schema change'), which is genuine when-to-use guidance. It offers no exclusion rule against list_constraints or generate_fk_cascade_graph, so an agent must infer which tool wins when both could answer.

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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