# Your connected sources

## How does your agent call a source?

Every source connected in the workspaces you granted your agent is reachable through Vistazo's MCP
server. MCP is the open standard your agent uses to reach Vistazo. Your agent reaches a database or
app connected in Vistazo without adding another server or holding any credentials. Vistazo runs each
call with the connection's stored credentials.

Four tools on the server carry every source:

1. `search_tools` finds a tool by keywords, by source, or both. Each match names the tool that runs it.
2. `describe_tool` returns that tool's arguments.
3. `call_tool` runs a tool that only reads.
4. `call_write_tool` runs a tool that changes something. Your client asks you before each call.

Each source tool is named `<source>__<tool>`, such as `economy__series_observations` or
`salesforce__list_leads`. The `/mcp/full` address also lists every source tool under that name, for
clients that load tools only when they need them ([Connect your own agent](/docs/mcp/connect)). A
call by that name runs on every address.

`search_tools` finds a source the moment you connect it. A client on `/mcp/full` keeps the tool list
from when it last loaded it, so reload the list or restart the client to see the new tools there.

## Which workspace does a call run in?

Every call runs in a workspace you ticked on the consent screen, and the server refuses a call that
names any other, whatever the client sends. `get_me` takes no arguments and lists your workspaces,
marking each one this connection cannot reach as `reachable: false`. Each reachable workspace also
lists its connected sources, with how many tools each holds. Every other core tool takes a
`workspaceId`, apart from `search_tools` and `describe_tool`, and the server never assumes one.

Each source tool, and each dataset tool, takes an optional `workspaceId`. With one workspace granted, your agent can leave
it out. With several, a call that leaves it out runs in the workspace that has the tool, if only one does.
If more than one has it, the call is refused and the reply lists the workspaces to choose from.

A tool connected in only some of your workspaces says in its description where it is available.

## Which tools can your agent call?

The permission set on each tool under **Settings → Connections** decides what your agent can call.
[Connections](/docs/data/connections) covers how to set it.

| Permission | On this server |
|---|---|
| **Allowed** | Found by `search_tools`, and runs |
| **Ask first** | Found, then refused, because Vistazo has no way to ask you on this path |
| **Blocked** | Not found |

Your client asks you before every `call_write_tool` call, even for a tool set to **Allowed**,
because that one tool runs every write. On `/mcp/full` a source tool called by its own name
carries its own marking instead, so an allowed write runs without the prompt.

The hosted sources offer only their read-only tools. A workspace where you are a guest adds no source
tools, and a call into it is refused. The same holds where your license lets you view but not build.

A source tool is for asking a source directly. A widget's pipeline names the connection and its tool
separately, as `mcpId` and `toolName`, and `update_widget`'s `pipeline` refuses a `<source>__<tool>`
name.

## What does a source tool return?

A source tool returns the source's own result. A result over 100,000 characters is cut, with a note
asking your agent to narrow the arguments.

Each MCP connection, one client signed in once, may run 300 data fetches an hour. Source calls, the
refreshes your agent starts and the test run of a new pipeline all count toward it.

## Which hosted sources are on the server?

The five public sources Vistazo hosts are reached the same way, through `search_tools` and
`call_tool`. They have no address of their own to add.

| Source | What it covers |
|---|---|
| [Countries](/docs/mcp-tools/curated-countries) | Global indicators, country by country |
| [Weather](/docs/mcp-tools/curated-weather) | Weather, earthquakes, alerts and storms |
| [Markets](/docs/mcp-tools/curated-markets) | Public company financials and stock prices |
| [Economy](/docs/mcp-tools/curated-economy) | US macro, federal fiscal data and exchange rates |
| [Wikipedia](/docs/mcp-tools/curated-wikipedia) | Article page views and the most-read articles |

The tools that read your uploaded files are core Vistazo tools, documented under
[Datasets](/docs/mcp-tools/datasets). Calling a source tool is free, the hosted sources included.
[Metering](/docs/mcp/overview#what-does-a-tool-call-cost) has the details.