Performance

Tetsu adds a fraction of a microsecond of processor time per request over a handler written for Bun.serve directly. This page shows the numbers and what they do not cover. The full method and every reading are in bench/README.md.

Processor time per request

Four routes, the same in every target: GET /ping; GET /users/:id behind a hook that adds user and an observer after the response; POST /items with a validated JSON body; and a 404. Microseconds per request, lower is better — Bun 1.4.2 on an Apple M5 Pro, medians of three interleaved rounds (2026-09-27):

	ping	users + 2 hooks	POST, validated	404
raw Bun	4.78	4.81	5.85	4.82
Tetsu	4.95	5.09	6.60	5.13
Elysia 1.4.30	4.89	5.13	6.31	4.91
Elysia 2.0.0-beta.16	5.07	5.47	6.29	5.10
Hono 4.13.8	5.16	5.87	6.88	5.41

Tetsu adds 0.17–0.75 µs a request over raw Bun and keeps 90–97% of its throughput. It is ahead of Hono on every route. Against Elysia 1.4, which compiles a function per route ahead of time, it is level on the GETs and 0.22–0.29 µs behind on the 404 and the validated POST.

Processor time is the number to compare, because it does not depend on whether the load generators kept up. Requests per second and latency are in the full report.

Startup and memory

	startup	slowest first request	idle RSS	peak RSS under load
raw Bun	3 ms	0.28 ms	14.3 MB	38–53 MB
Tetsu	5 ms	0.51 ms	21.7 MB	47–59 MB
Hono	6 ms	1.17 ms	22.1 MB	51–60 MB
Elysia 1.4.30	24 ms	2.15 ms	38.3 MB	59–72 MB
Elysia 2 beta	13 ms	2.24 ms	41.2 MB	65–77 MB

The benchmark loads Tetsu from its sources. The published packages are bundled and idle at 14.1 MB. No target grows its heap after load.

The cost of the types

On every change, CI measures the compiler’s work for a generated application of 200 routes and fails if it goes over budget:

routes	types	instantiations	memory	check
2	10 648	27 218	56 MB	0.03 s
200	30 857	235 422	83 MB	0.12 s
800	92 057	866 322	166 MB	0.45 s

TypeScript 7.0.2. The cost grows linearly, about 800 instantiations a route. The same application written as one chain, the shape Elysia’s and Hono’s typed clients need, costs 330–408 thousand instantiations at 200 routes and 2.75–3.04 million at 800.

Validation

Validation goes through Standard Schema, so its cost is the library’s. From bun run --cwd bench validators, in nanoseconds per check:

	Zod 4.6	ArkType 2.2	Valibot 1.5	TypeBox via tb()
small body, valid	23	24	21	6.7
20-item body, valid	922	168	784	52
20-item body, one item invalid	1,020	3,260	936	21,090
memory to import	+21 MB	+57 MB	+3 MB	+36 MB

TypeBox’s error path is the slowest of them: with issues: "summary" the invalid body above takes 76 ns.

Reproducing

git clone https://github.com/tetsujs/tetsu && cd tetsu
bun install
bun run --cwd bench http

Every target and every load generator runs in its own process. ROUNDS=3 interleaves rounds and reports medians; ONLY= picks targets. bun run --cwd bench types, validators and cost run the other measurements.

What these numbers do not say

• They come from one machine and one level of concurrency.
• The load generator counts responses but does not check their bodies.
• The routes are small. In an application that talks to a database, the framework’s share of each request is smaller still.
• Two runs back to back behave like two different machines. Compare targets within one run, with the baseline in it.