---
title: "Puts the preview of a feature online"
method: POST
path: "/lambdas/{privateKey}/features/{feature}/preview/start"
tags: ["Features"]
---

# Puts the preview of a feature online

`POST /lambdas/{privateKey}/features/{feature}/preview/start`

## Request

- Base URL: `https://genhttp.dev/api/v1`
- URL: `https://genhttp.dev/api/v1/lambdas/{privateKey}/features/{feature}/preview/start`
- Auth: none declared

Compiles the feature's files and serves them at its `previewPath`, `/features/{feature}/` on this site, against its
own copy of the data. Nobody is sent there; it is reached by its address only. The lambda is not touched.

Links inside a lambda's pages should be relative: a feature answers below `/features/{feature}/`, where a link that
starts with a slash leaves it.

## Path parameters

- `privateKey` string, required
- `feature` string, required

## Response `200`

The preview is online.

- FeaturePreviewResponse: What came of putting the preview of a feature online.
  - `Success` boolean: Whether it compiled and the preview is online with it
  - `Feature` FeatureResponse: A feature: a change being worked on beside the lambda.
    - `Key` string: What every call about it takes, and what its preview is reached by
    - `Name` string: What it is, in a few words
    - `Branch` string: The branch it is in the lambda's git repository - given when it starts, and kept when it is renamed
    - `Specification` string, nullable: What the user wants from it and why
    - `Change` string, nullable: What it changes, in one line
    - `Base` integer: The version it is based on
    - `Newest` integer, nullable: The newest version of the lambda
    - `Mergeable` boolean: Whether it can be merged: it is based on the newest version
    - `Origin` string, nullable: How it was started: `api`, `agent` or `git`
    - `Created` string, date-time: When it was started
    - `Modified` string, date-time: When it was last saved or changed
    - `Online` boolean: Whether its preview is online
    - `Current` boolean: Whether its preview is online and serves what the feature holds now, rather than an earlier save
    - `Previewed` string, date-time, nullable: When its preview was last put online, while it is
    - `PreviewPath` string: Where its preview answers on this site, whether it is online or not: `/features/{key}/`
    - `Revision` integer: How many times its files were saved, counting the ones it began with. Passed back with a save, it keeps that save from replacing one made elsewhere.
  - `Diagnostics` CompilationDiagnostic[]: What the compiler said: the errors that kept it offline, or the warnings of a preview that went online
    - `Severity` string: `Error`, which keeps the code from going online, or `Warning`
    - `Id` string: What kind of message it is: the C# compiler's (`CS1002`), `LAMBDA0001` for something lambdas may not do, `LAMBDA0002` for a handler the platform cannot serve, or `LAMBDA` for anything else the platform refused
    - `Message` string: What is wrong, and often what to do about it
    - `Line` integer: The line in the file, counting from 1; 0 when it is about no line
    - `Column` integer: The column in the line, counting from 1; 0 when it is about no line
    - `File` string, nullable: The name of the file it is in, as the lambda names it; absent when it is about none of them

## Other responses

- `404`: No lambda has this editor key, or the lambda has no feature with this key: it never existed, or it was merged or deleted.
- `422`: The code does not compile. `diagnostics` holds what the compiler said; whatever the preview served before, it still serves.

---

[API](https://skmtc.dev/genhttp/apis/genhttp-lambda-api.md) · [All operations](https://skmtc.dev/genhttp/apis/genhttp-lambda-api/llms.txt) · [OpenAPI document](https://skmtc.dev/genhttp/apis/genhttp-lambda-api/revisions/8b36699e03df?raw)