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MCPg - Production-grade PostgreSQL MCP Server

MCPg - Production-grade PostgreSQL MCP Server

by devopam
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

Read PG WAL records

read_pg_wal_records
Read-only

Read PostgreSQL Write-Ahead Log records over a specified LSN range for inspection; requires pg_walinspect and indicates if the extension is unavailable.

Instructions

Read Write-Ahead Log (WAL) records information over a specified LSN range. Requires the pg_walinspect extension. If not installed, returns available=false.

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": {
      "start_lsn": "<start_lsn>"
    },
    "name": "read_pg_wal_records"
  }
}

Input Schema

NameRequiredDescriptionDefault
limitNo
end_lsnNo
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.
start_lsnYes

Output Schema

NameRequiredDescriptionDefault
recordsYes
availableYes

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
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 genuinely extra behavior: the dependency on the pg_walinspect extension and the graceful degradation to an available=false response when it is absent, which is exactly the kind of thing an agent needs to interpret a result.

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 short sentences, front-loaded with the operation and scope, followed by the prerequisite and failure mode. No filler and nothing wasted.

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

Completeness3/5

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

An output schema exists, so return values need not be described, and the extension caveat is valuable. However, for a four-parameter tool with 25% schema coverage, the missing LSN format and limit semantics leave the agent under-informed about how to construct a valid call.

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

Parameters2/5

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

Schema description coverage is only 25% — only the database parameter carries prose. The description mentions an LSN range but gives no LSN syntax or format guidance for start_lsn/end_lsn, and says nothing about limit (default 100) or how the range interacts with it. With low coverage the description should compensate and does not.

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 uses a specific verb (Read) plus a specific resource (Write-Ahead Log records) and states the scope (a specified LSN range), which is much clearer than a tautology. It does not, however, distinguish itself from nearby siblings such as read_pg_wal_stats, get_wal_archive_status, or get_current_wal_lsn, so an agent must infer the boundary.

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?

The prerequisite (pg_walinspect extension) and the fallback behavior (available=false) are useful context, but there is no explicit when-to-use or when-not-to-use guidance relative to the other WAL and stats tools. Usage is only implied by the LSN-range phrasing.

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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