Write Tools

Write Tools

The server is read-only by default. One optional write tool exists, and it is off unless you turn it on.

What it does

Setting ENABLE_CHARGING_WRITES=true registers:

set_charging_cost(charging_process_id, cost) — sets the total cost of one charging session. This is the same field TeslaMate's own UI lets you edit. Find the session id with search_charging_sessions first.

It also registers a backfill_costs_from_receipts prompt that walks through matching receipts to sessions.

The real boundary is the database grant

Do not rely on the application flag alone. Give the role write access to that single column and nothing else:

GRANT UPDATE (cost) ON charging_processes TO teslamate_ro;

With that grant in place, PostgreSQL itself refuses any other write, regardless of what the application does. The write path is a single hand-written parameterized UPDATE … WHERE id = … — the declarative .sql/.toml query registry stays read-only by design and never routes through it.

run_sql remains read-only no matter what: it runs in a READ ONLY transaction with a forced rollback.

Confirmation behaviour

On clients that support MCP form elicitation, the user is shown a confirmation dialog before each write, quoting the session id and the new cost.

Clients without form elicitation proceed without a confirmation step. This is deliberate — portal-fronted connectors have no back channel to ask through — but it means the elicitation dialog is a convenience, not a security control. The grant is the control.

Turning it off

Unset ENABLE_CHARGING_WRITES (or set it to false) and the tool disappears from tools/list. Revoking the grant is the belt-and-braces version:

REVOKE UPDATE (cost) ON charging_processes FROM teslamate_ro;