exsqlain

Status: archived (2026-06-30). A finished thought, not a maintained tool.

The idea

A dev-loop tool for Haskell + Postgres work. The library:

1. Runs EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS, FORMAT JSON) against a connection,
2. Pushes the resulting plan over Server-Sent Events to an embedded pev2 (Dalibo's Postgres plan visualizer) frontend,
3. Uses persistent global channels (unsafePerformIO) specifically so that reloading your hspec specs under ghcid keeps the browser connection alive.

The payoff was a tight loop: edit a query in your test suite, and the EXPLAIN ANALYZE plan re-renders live in the browser on every ghcid reload — see the plan of the query under your cursor as you tweak it.

Why it's archived

• The product angle was always thin. The hard part is visualizing the plan, and that is pev2 — which this just embeds. Pasting a plan into the free hosted explain.dalibo.com or explain.depesz.com takes two seconds.
• The live-loop angle is now gone too. The premise was a human in a tight edit/look loop. Agentic coding changes the loop: an agent edits the query and reads textual/JSON output — it gets nothing from a rendered browser visualization. That inverts which half of this project mattered: the interesting engineering (SSE plumbing, the Vue app, the persistent-channel trick) is exactly the part that no longer has an audience.
• What survives is trivial. The only durable bit is "given a connstr + query, return the EXPLAIN ... FORMAT JSON plan as structured data" (see runQuery in src/Database/PostgreSQL/Exsqlain.hs). That's ~20 lines and needs no library; an agent just runs the EXPLAIN itself.

If the value ever migrates anywhere, it's to a language-agnostic agent-facing EXPLAIN tool (an MCP server: "analyze this query, here's the plan + the bottleneck"). That would reuse nothing here except the one trivial line, so it's a start-fresh idea, not a revive.

State of the code

This never got past a 2020 prototype: ~131 lines of Haskell, a ~90-line Vue 2 app (Vue 2 is itself EOL), placeholder package metadata, and a couple of known rough edges (runQuery uses EXPLAIN ANALYZE, which executes the statement — fine for SELECT, not for writes). Left as-is for reference.