AppTheory — Multi-language Serverless Application Framework (Go, TypeScript, Python)

AppTheory is a TableTheory-style multi-language monorepo for building serverless applications with a shared runtime contract and cross-language drift prevention.

Distribution: GitHub Releases only (no npm/PyPI publishing).

Charter (M0)

AppTheory exists to provide a portable runtime core (and contract tests) for AWS serverless applications that must be first-class in Go, TypeScript, and Python.

Target audiences and use cases:

• Platform and application teams building HTTP APIs on AWS Lambda (Lambda Function URL, API Gateway v2).
• Event-driven workloads (SQS, EventBridge, DynamoDB Streams) and WebSockets are required for Lift parity and are tracked as remaining contract work (see docs/development/planning/apptheory/apptheory-gap-analysis-lesser.md).
• Internal tooling and shared libraries that need consistent request/response semantics across languages.

Non-goals (near-term):

• Not a general-purpose web framework; contract-first serverless runtime only.
• Not registry-published packages (no npm or PyPI); releases ship via GitHub assets.

Public Names (M0)

• Go module path: github.com/theory-cloud/apptheory
• Go runtime package: github.com/theory-cloud/apptheory/runtime
• npm package: @theory-cloud/apptheory
• Python distribution name: apptheory
• Python import name: apptheory

Supported Runtimes (M0)

• Go toolchain: 1.26.1
• Node.js: 24
• Python: 3.14

Documentation

• Main docs index: docs/README.md
• TypeScript package docs: ts/docs/README.md
• Python package docs: py/docs/README.md
• CDK package docs: cdk/docs/README.md

Runtime tiers (P0/P1/P2)

• P0: routing + request/response normalization + error envelope
• P1: request-id, tenant extraction, auth hooks, CORS, size/time guardrails, middleware ordering
• P2 (default): P1 + observability hooks + rate limiting / load shedding policy hooks

Security & production notes

• CSRF protection and secure cookie flags are application concerns; set Secure/HttpOnly/SameSite explicitly in Set-Cookie.
• Request IDs can be supplied via x-request-id; validate/override if your threat model requires it.
• Retries/backoff for event sources are handled by AWS trigger settings (retry policies, DLQs/redrive), not by the runtime.

Go runtime (P2 default)

The Go runtime implements the fixture-backed contract across P0/P1/P2 tiers (default: P2).

Notes:

• Header names are case-insensitive, but Request.Headers / Response.Headers keys are canonicalized to lowercase.
• If two routes are equally specific, the router prefers earlier registration order.

Minimal local invocation:

env := testkit.New()
app := env.App()

app.Get("/ping", func(ctx *apptheory.Context) (*apptheory.Response, error) {
	return apptheory.Text(200, "pong"), nil
})

resp := env.Invoke(context.Background(), app, apptheory.Request{Method: "GET", Path: "/ping"})
_ = resp

To force the P0 core (minimal surface area), pass apptheory.WithTier(apptheory.TierP0) when creating the app.

Unit test without AWS (deterministic time + IDs + HTTP event builder):

func TestHello(t *testing.T) {
	env := testkit.NewWithTime(time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC))
	env.IDs.Queue("req-1")

	app := env.App()
	app.Get("/hello", func(ctx *apptheory.Context) (*apptheory.Response, error) {
		return apptheory.MustJSON(200, map[string]any{
			"now_unix": ctx.Now().Unix(),
			"id":       ctx.NewID(),
		}), nil
	})

	event := testkit.APIGatewayV2Request("GET", "/hello", testkit.HTTPEventOptions{
		Headers: map[string]string{"x-request-id": "request-1"},
	})
	resp := env.InvokeAPIGatewayV2(context.Background(), app, event)

	if resp.StatusCode != 200 {
		t.Fatalf("expected status 200, got %d", resp.StatusCode)
	}
	if resp.Headers["x-request-id"] != "request-1" {
		t.Fatalf("expected x-request-id request-1, got %#v", resp.Headers["x-request-id"])
	}

	var body map[string]any
	if err := json.Unmarshal([]byte(resp.Body), &body); err != nil {
		t.Fatalf("parse response json: %v", err)
	}
	if body["id"] != "req-1" {
		t.Fatalf("expected id req-1, got %#v", body["id"])
	}
}

Start here:

• Planning index: docs/development/planning/apptheory/README.md
• Main roadmap: docs/development/planning/apptheory/apptheory-multilang-roadmap.md
• Import pipeline support pack reference example (CDK + handlers): examples/cdk/import-pipeline/

Migration:

• Lift → AppTheory (draft): docs/migration/from-lift.md

License:

• Apache 2.0 (see LICENSE)