Scripting Overview

Most checks need no code at all — the declarative [assert] block covers status codes, JSON paths, headers, and timing. When you need real logic, Napper lets you script in the language you already use.

There is no "preferred" language. Use whatever your team already tests with. .fsx and .csx happen to be genuinely lovely — concise, strongly typed, immutable by default — but they are never required.

One surface, every language (spec: script-context, script-runner)

Every language sees the same two objects:

• ctx — the request/response context for pre/post hooks: ctx.vars, ctx.request, ctx.response, ctx.set(...), ctx.fail(...), ctx.log(...).
• nap — the orchestration runner for script-driven flows: nap.run(...), nap.runList(...), nap.vars, nap.fail(...).

The same post-script in four languages:

// validate-user.js
import { ctx } from "napper";
const user = ctx.response.json;
if (user.id !== ctx.vars.userId) ctx.fail("User ID mismatch");
ctx.set("token", user.sessionToken);

# validate_user.py
from napper import ctx
user = ctx.response.json
if user["id"] != ctx.vars["userId"]:
    ctx.fail("User ID mismatch")
ctx.set("token", user["sessionToken"])

// validate-user.fsx
let user = ctx.Response.Json
if user.GetProperty("id").GetString() <> ctx.Vars["userId"] then ctx.Fail "User ID mismatch"
ctx.Set "token" (user.GetProperty("sessionToken").GetString())

// validate-user.csx
var user = ctx.Response.Json;
if (user.GetProperty("id").GetString() != ctx.Vars["userId"]) ctx.Fail("User ID mismatch");
ctx.Set("token", user.GetProperty("sessionToken").GetString());

Real runtimes, no sandbox

Unlike the sandboxed JavaScript in Postman and Bruno, Napper scripts run on real runtimes — Node.js, Python 3, or .NET — with full access to npm, PyPI, and NuGet. Parse XML, call a database, generate a JWT, validate a schema, or pull in any package.

How to reference a script (spec: nap-file, script-dispatch)

Reference scripts from a .nap file's [script] block, or use a script file as a .naplist step. Dispatch is by extension, so a single playlist can mix languages:

[steps]
./auth/01_login.nap
./scripts/seed-data.js          # JavaScript step
./scripts/parametrized-tests.py # Python step
./teardown/cleanup.nap

Zero install (spec: script-sdk)

The Napper binary bundles the JavaScript and Python SDKs and puts them on the runtime's module path, so import { ctx } from "napper" (JS) and from napper import ctx (Python) just work — no npm install, no pip install. The published @nimblesite/napper (npm) and napper (PyPI) packages are conveniences for editor autocomplete and explicit vendoring.

Requirements (spec: script-runtime)

The Napper binary itself is self-contained with no runtime dependencies. Script hooks need the relevant runtime only for the language you actually script in — a JavaScript shop never installs .NET, and a .NET shop never installs Node. See Installation.