# Coding agents (/docs/agents)

Give your agent one prompt:

```text
Add coss.com to this project: read https://coss.com/llms.txt, get a development key with `npx coss-cli init`, and build and test with it.
```

From there the agent reads what it needs from the docs, asks you to approve a development key
in your browser, installs the SDK and tests its code with that key. Nothing it sends is
delivered until you switch to a production key yourself.

## What agents read [#what-agents-read]

- **[/llms.txt](/llms.txt)** starts with a short brief (how to get a key, how the SDK reports
  errors, how to test webhooks), then lists every docs page.
- **Every docs page is Markdown** at its URL plus `.md`: [/docs/email/sending.md](/docs/email/sending.md).
  The HTML pages point to it too (`<link rel="alternate" type="text/markdown">`), and each has a
  **Copy Markdown** button for pasting it into a chat yourself.
- **API reference pages** list each operation's method and URL, parameters, request body,
  responses and errors, with examples for the TypeScript SDK, HTTP and the
  [other SDKs](/docs/sdks): [/docs/api-reference/emails/send-email.md](/docs/api-reference/emails/send-email.md).
  The [OpenAPI 3.1 document](https://api.coss.com/openapi.json) describes the same API.
- **[/llms-full.txt](/llms-full.txt)** is every guide in one file, with a short entry per API
  operation. It's large: agents usually do better fetching the pages they need.

## Development keys [#development-keys]

`npx coss-cli init`, run in the project, gets the agent a key without you copying one around: it
opens the dashboard, you check the code and approve a key for that project (development
environments only), and the [CLI](/docs/cli#set-a-project-up) writes it to `.env.local` (Next.js)
or `.env` as `COSS_API_KEY` and installs the `coss` package. Where no browser can open (over SSH,
in a container or an agent's cloud sandbox), it prints a link instead and waits for the code that
page shows, typed into the terminal: run it yourself there.

Development keys work with every API and never deliver anything; emails and SMS get simulated
outcomes, events and webhooks (see [sandbox behaviour](/docs/environments#sandbox-behaviour)).
So the agent can run what it writes, and `coss listen` forwards the resulting webhooks to its
local handler.

`npx coss-cli init --agents` also adds a short coss.com section to the project's `AGENTS.md` (or
`CLAUDE.md`), so later sessions know where the docs are and how to test without reading this
again.

## Claude Code plugin [#claude-code-plugin]

The coss.com plugin gives Claude Code a skill for building with coss.com (loaded when a task
involves it) and the [MCP server](/docs/mcp):

```text
/plugin install coss --marketplace cosscom/coss
```

On Claude Code before 2.1.275, add the marketplace first: `/plugin marketplace add cosscom/coss`,
then `/plugin install coss@coss`.

It asks for an API key for the MCP server. Use a development key (`coss_test_…`), or leave it
empty: the server's docs tools work without one.

## Cursor, Codex and other agents [#cursor-codex-and-other-agents]

The same skill installs into Cursor, Codex, GitHub Copilot, Windsurf and other agents with the
[skills CLI](https://github.com/vercel-labs/skills):

```sh
npx skills add cosscom/coss
```

Add the [MCP server](/docs/mcp) as well to let the agent search these docs, look up emails and
SMS, and explain why one wasn't delivered.