Show HN: Pglens – 27 read-only PostgreSQL tools for AI agents via MCP

Most Postgres MCP servers expose query and list_tables. Agents end up guessing column values, enum casing, and join paths - then retrying until something works.

pglens gives agents the context to get it right the first time: column_values shows real distinct values with counts, find_join_path does BFS over the FK graph and returns join conditions through intermediate tables, describe_table gives columns/PKs/FKs/indexes in one call. Plus production health tools like bloat_stats, blocking_locks, and sequence_health.

Everything runs in readonly transactions, identifiers escaped via Postgres's quote_ident(), no extensions required. Works on any Postgres 12+ (self-hosted, RDS, Aurora, etc.). Two dependencies: asyncpg and mcp.

https://github.com/janbjorge/pglens

pip install pglen

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This is really nicely, read only is the right way to start

Thanks! Read-only felt like the obvious constraint; agents shouldn't need write access to understand a database.

Read-only by design is a smart constraint for agent tooling — eliminates a whole class of "oops the LLM dropped my table" failure modes. Curious about a couple things: how do you handle schema introspection? Do the tools auto-discover tables/columns or is there a config step? And for the query tools, is there any cost/complexity guardrail (e.g. preventing a full sequential scan on a 500M row table)?