pretix-agent-mcp: Skill for Claude Code

Adding a pretix tool

Read tools/events.py first — it is the reference implementation, and matching it is faster than reading this twice. The rules that are not obvious from it are below.

1. Check what pretix actually offers

Fetch https://docs.pretix.eu/dev/api/resources/<resource>.html and confirm the endpoint path, the required fields on create, and the exact field names. A wrong path is the most common failure here, and memory is not good enough — the docs also contain a few singular/plural typos where the DRF router registers the plural form (quotas/{id}/, not quota/{id}/).

If pretix cannot do the thing: implement the subset that exists and add the gap to "Known limits" in the README. Never scrape the UI, use an admin session, or call an undocumented endpoint.

2. Write the function

@tool("read")
async def list_quotas(app: App, event: str, limit: int = 50) -> dict:
    """First line is what the model sees when deciding whether to call this.

    Say what it does not do, and name the better tool when there is one. This docstring is
    the tool description — it is the only documentation the agent gets.
    """
    quotas, total, truncated = await app.pretix.paginate(
        "events", app.check_event(event), "quotas", cap=page_size(limit)
    )
    return listing([pick(q, "id", "name", "size") for q in quotas], total=total, truncated=truncated)

• First parameter is always app: App. Everything after it is agent-supplied and becomes JSON Schema from its annotation, so annotate concretely (str, int, bool, list[str], dict[str, Any], str | None = None). A default makes it optional. No *args/**kwargs. Return -> dict.
• Name the event-slug parameter event. The registry keys the event allowlist and the live-event guard on that exact name; any other name silently loses both.
• Validate everything that becomes a path segment: app.check_event(event) (validates and enforces the allowlist), object_id(value, field="quota_id"), order_code(code), page_size(limit). Raise ValidationError for anything else malformed, before the request is built.
• Never redact, audit, or check capabilities in a tool — the registry does all three.
• Reuse tools/_shared.py: i18n() flattens pretix's {"en": ...} fields, pick() subsets an object, clean() drops None so a PATCH only touches what the agent named, listing() gives lists a uniform shape.
• Reject an empty update (if not payload: raise ValidationError(...)) rather than sending a no-op PATCH.
• Prices are decimal strings ("23.00"). Annotate the parameter str and list it in the decorator's money=(...) — the registry validates declared amounts through validate.price() before a high-risk call is queued for approval, which a tool body cannot do because it does not run until after the approval. Sum with Decimal.