Glossary

Here are the terms Fountain uses, and the five that carry more than one meaning. Where a word has more than one sense, this page lists the senses and names the one the docs use.

The overloaded words

Agent

Three senses. The docs mean the first.

1. The primitive. A named configuration that you can run again and again. Read About agents.
2. The coding agent. The process in the sandbox, which is Claude Code, Codex, Gemini CLI or opencode. The docs call this the runtime.
3. The ACP role. In the Agent Client Protocol, the process an editor spawns. The docs call this fountain acp. Read fountain acp.

Environment

Three senses. The docs mean the first.

1. The primitive. Read About environments.
2. Environment variables. The values in a process. The docs always write "environment variables" in full.
3. A deployment tier. Dev, staging, production. The docs say deployment for this, and never "environment".

Fountain

Three senses. The format tells you which.

1. Fountain, unstyled, is the product.
2. fountain, in code font, is the CLI binary.
3. the fountain skill is the skill that each sandbox gets, which gives an agent Fountain's own API. Always write the word "skill" with it.

Vault

Two senses, and they are close to opposite. The docs mean the first.

1. The primitive. A small, static override layer for one run, which wins on a key collision. Read About vaults.
2. HashiCorp Vault. A central server that issues dynamic leased credentials. Nothing about it relates to Fountain's Vault, except the shape of the encryption. The Vault page sets the collision out.

Computer

The team and conversations apps use this word for the machine a teammate works on. The docs say sandbox.

The rest

Term	Means
ACP	Agent Client Protocol. How an editor or a chat surface drives Fountain. Read fountain acp.
AG-UI	The protocol that OpenBot and other coworker hosts speak. Read OpenBot.
Conversation	One run of an Agent in a sandbox. Read About conversations.
DEK	Data encryption key. Fountain derives one for each tenant from MASTER_SECRETS_KEY, then encrypts that tenant's secrets with it.
Inference credentials	A user's own model provider keys, which they enter in the app. An operator never sets them. Read Services Fountain uses.
Log event	One entry in a conversation's stream. It arrives over SSE, and ?blocks=true parses it for you.
MCP server	A Model Context Protocol server that an Agent gives its runtime. You declare it in mcp_servers.
Reaper	The background sweep that suspends an idle sandbox, and destroys one that passed a configured ceiling.
Runner	A machine you own that runs fountain runner and acts as a sandbox provider. Read Self-hosted runners.
Runtime	The coding-agent CLI that a sandbox runs. One of claude, codex, gemini, opencode.
Sandbox	The isolated machine that a Conversation runs in. Several Conversations can share one. Fountain provisions it at launch and reclaims it on the lifetime rules. GET /api/sandboxes lists them.
Sandbox provider	A backend that Fountain provisions sandboxes on. Sprites, E2B, Daytona, or a self-hosted runner. Read the sandbox contract.
Skill	A SKILL.md that Fountain writes into the sandbox, inline or from GitHub.
Sprite	One sandbox on the Sprites provider. Not a Fountain concept. Read Sprites.
Substitution	${VAR} interpolation in an Agent config, resolved from the merged secrets at spawn.
Suspend	To scale a sandbox to zero and keep its disk, so the agent's memory survives.
Teammate	An Agent with one Conversation that continues, on the reserved channel fountain:team. Not a primitive. Read Agents as teammates.
Turn	One prompt, and the work that comes after it, in a Conversation.

Two things that sound like primitives and are not

A team is not an object. Read Agents as teammates.

A sandbox is not an object you create. Fountain provisions it when a Conversation starts. You can list one, put a second Conversation on it with sandbox_id, and reset a persistent one. Read Sandboxes and About conversations.