Feature Request: Align MCP instructions with --tool-filter (reduce ~9K wasted tokens)

[migliolirobertoeric-create]

Feature Request: Align MCP instructions with --tool-filter

Problem

When using --tool-filter to limit exposed tools, the MCP server correctly filters the tools available to the client. However, the server instructions sent via the MCP protocol still include documentation for ALL tool groups, regardless of the filter.

This means the AI client receives ~14,600 tokens of instructions in its system prompt, but ~8,800 tokens (61%) are for tool groups that aren't even exposed.

Example

Config:

{
  "command": "npx",
  "args": ["-y", "@neverinfamous/postgres-mcp", "--transport", "stdio", "--tool-filter", "starter,vector"],
  "env": { ... }
}

Tools exposed: 76/232 (correct — only starter + vector groups)

Instructions sent: ALL 25 sections including PostGIS, pgcrypto, ltree, citext, partitioning, pg_partman, pg_stat_kcache, cron, performance, monitoring, admin, backup, text, stats, introspection, migration — none of which have any tools exposed.

Impact

Metric	Value
Total instruction tokens	~14,600
Useful (matching filter)	~5,750 (39%)
Wasted (no matching tools)	~8,850 (61%)
% of 200K context window	4.4% wasted
% of 1M context window	0.9% wasted

For users on smaller context windows (200K), this is significant. The instructions block becomes the single largest component in the system prompt — larger than the user's project configuration and memory combined.

Proposed Solution

Align the instructions field sent during MCP initialization with the --tool-filter setting. Only include documentation sections for tool groups that have at least one tool exposed.

For example, with --tool-filter "starter,vector":

• Include: Critical Gotchas, Response Structures (filtered), API Mapping, Format Auto-Resolution, Vector Tools, JSONB Tools, Schema Tools, Transactions, Code Mode
• Exclude: Stats, Text, Performance, Monitoring, Admin, Backup, Partitioning, pg_partman, pg_stat_kcache, citext, ltree, PostGIS, Cron, pgcrypto, Introspection, Migration

This could also be a separate --instruction-filter flag for finer control.

Environment

• @neverinfamous/postgres-mcp v2.3.0
• Claude Code v2.1.75
• Transport: stdio

[neverinfamous]

I started implementing your suggestion and discovered, that at least in antigravity, the server instructions are being truncated far before complete receipt. Even the filtering you suggested was getting truncated. I think the solution is to move the bulk of the content into a folder of .md files for each tool group that the agent can pull as needed, with a minimal instruction set in the server instructions, along with MCP resources. If successful, it will be a few days or so until I get to postgres-mcp. I am currently working on db-mcp (sqlite).