hermes-yandex-calendar

Let your Hermes Agent run your Yandex Calendar. "What's on my calendar next week?" — "Move the standup to Thursday and invite Ann." — "Decline the 4pm." The agent reads and writes real events on your real calendar, over CalDAV, with no third-party service in the middle.

• 📅 Seven tools, one toolset — list, create, update, RSVP, move between calendars, delete, and enumerate the calendars themselves.
• 🔒 You choose what it may touch — restrict it to specific calendars, and to specific actions (read, read,write, …). A disallowed action is not in the toolset at all.
• 🛟 Careful with your data — recurrence rules, alarms, and properties this plugin does not model survive every edit (an edit does rewrite a timed start and end into UTC and drops the resource's VTIMEZONE, so a recurring series in a daylight-saving zone shifts by an hour after the changeover); an edit that would overwrite someone else's concurrent change is refused; moves copy the resource byte for byte, and the original goes only once the copy has been read back from the target and only if nobody changed it in between.
• 🔑 App password, not your account password — scoped to CalDAV, revocable in one click.

Tested against Hermes 0.19.x, Python 3.11–3.13.

Quick start

# 1. Install into Hermes (alternatively: pip install hermes-yandex-calendar)
hermes plugins install akinfold/hermes-yandex-calendar/hermes_yandex_calendar --enable

# 2. Add your credentials — the app password comes from
#    https://id.yandex.ru/security/app-passwords (scope: "Calendar (CalDAV)")
(umask 077 && printf 'YANDEX_CALENDAR_LOGIN=%s\nYANDEX_CALENDAR_APP_PASSWORD=%s\n' \
  'you@yandex.ru' 'your-app-password' >> ~/.hermes/.env)
chmod 600 ~/.hermes/.env

--enable writes the plugin's manifest name into ~/.hermes/config.yaml for you, so there is nothing else to switch on:

plugins:
  enabled: [yandex_calendar]

Installing with pip instead leaves that to you: third-party plugins are off until they are listed there.

That's it. Ask the agent "what do I have tomorrow?" and it will tell you.

The backward-compatible default exposes every action, including delete. For a new or untrusted agent setup, start with YANDEX_CALENDAR_ACTIONS=read — see Security boundaries.

The tools

Up to seven standalone tools, in the yandex_calendar toolset:

Recurring events are not expanded. yandex_calendar_list_events runs a plain time-range query and reports each event as the server stores it. A recurring series is listed once, with the start/end of its first occurrence — which can lie well before the requested range — and its recurrence rule is not part of the output. A series whose individual occurrences were edited comes back as several entries sharing one href, and update_event and respond_event refuse such a resource rather than drop those occurrences; it can still be moved or deleted as a whole.

Yandex Calendar has no public REST API, so this plugin speaks CalDAV (https://caldav.yandex.ru) directly — the same protocol Yandex's own docs point third-party clients at. Nothing is proxied through anyone else's servers.

Multiple calendars

yandex_calendar_list_events and yandex_calendar_create_event take an optional calendar argument; yandex_calendar_move_event takes a required one, naming the destination. A calendar is named by its display name (as returned by yandex_calendar_list_calendars), by the last segment of its path (e.g. events-12345), or by its full href — names and path segments are matched case-insensitively. Omit the optional argument to use the default calendar. update, respond, move, and delete identify the event by its event_href, which already encodes the calendar it lives in.

Restrict which calendars the plugin may touch with YANDEX_CALENDAR_CALENDARS, and put the one you want as the default first: that order is what yandex_calendar_list_calendars reports and what an unqualified write follows. Without the setting, the order the server returns stands.

Changed in 0.5.0. Until then the order of that setting was ignored and the default was whichever allowed calendar the server happened to list first. If you set YANDEX_CALENDAR_CALENDARS and relied on that, check which calendar your value names first before upgrading — it is the one events will go to now. An entry that matches nothing is skipped, so a typo in first position hands the default to the next entry that does match.

Some Yandex calendars — holidays and birthdays, for instance — are read-only, yet they are listed like any other and the server answers a write into them with success while storing nothing. yandex_calendar_move_event catches this, because it reads the copy back and leaves the original where it was, but yandex_calendar_create_event does not: it reports created: true and an href at which nothing exists. Keep such calendars out of reach with YANDEX_CALENDAR_CALENDARS.

Configuration

Credentials are read from the environment first, then from ~/.hermes/.env, so they work in gateway and subprocess runs. Secret values are never logged.

Dates and times are ISO 8601 (2026-07-25 or 2026-07-25T14:00:00+03:00); a datetime without an offset is treated as UTC.

Restricting what the agent can do

YANDEX_CALENDAR_ACTIONS decides which of the seven tools are registered at all. A disallowed action is not merely refused at call time: the tool never appears in the agent's toolset, so it cannot be invoked, and the model is not tempted to try.

Accepted values, comma-separated and case-insensitive — individual actions (list_calendars, list_events, create_event, update_event, respond_event, move_event, delete_event), full tool names (yandex_calendar_delete_event), or the shorthands:

# Look, but don't touch:
YANDEX_CALENDAR_ACTIONS=read

# Full scheduling, but the agent can never delete anything:
YANDEX_CALENDAR_ACTIONS=read,write

# Just enough to answer invitations:
YANDEX_CALENDAR_ACTIONS=list_events,respond_event

Leave it unset for all seven tools; an empty or whitespace-only value counts as unset, so YANDEX_CALENDAR_ACTIONS= does not mean "no tools". A name that matches nothing is ignored, so a typo can only ever withhold a tool, never grant one — and a non-blank value that names nothing recognisable therefore registers nothing at all. The list is applied when the plugin loads: restart Hermes after changing it.

Security boundaries

• CalDAV credentials are sent only to the HTTPS origin configured by YANDEX_CALENDAR_BASE_URL. Event hrefs pointing to HTTP or another origin are rejected before a request is made. Cross-origin redirects do not receive the authorization header.
• YANDEX_CALENDAR_CALENDARS applies to both target calendars and direct event operations (update, respond, move, and delete). Event paths are canonicalized before the allow-list check and the same canonical path is sent; moves validate both the source and destination calendar.
• Calendar titles, descriptions, locations, and attendee names are untrusted input. A capable agent can still act on misleading event content, so use read unless the agent and every calendar writer are trusted. Attendees supplied to a tool must be mailbox addresses, while server-provided calendar addresses are preserved for compatible invitation updates. Line breaks are rejected during serialization to prevent CRLF property injection.
• Edits are conditional. The plugin writes an event back only if it still matches the version it read (If-Match with the resource's ETag), so an agent cannot silently overwrite a change you made meanwhile in the Yandex web UI, on a phone, or from another client. When that happens the tool says so and the agent can re-read the event and reapply its change. A move is conditional at the same point: the original is removed only if it still matches the copy that was just written, and if it changed in between the event is left in both calendars with a message saying so, rather than losing that change.
• The action allow-list limits the tools exposed to Hermes; it does not reduce the privileges of the Yandex app password itself. Use a dedicated app password and, for stronger isolation, a dedicated Yandex account.

The default remains all for compatibility with existing installations. This is a trusted-agent mode, not the recommended starting point for a new deployment.

Getting the app password

CalDAV does not accept your normal account password.

1. Open https://id.yandex.ru/security/app-passwords.
2. Add a password with the Calendar (CalDAV) scope.
3. Copy it into YANDEX_CALENDAR_APP_PASSWORD — it is shown only once, and you can revoke it at any time without touching your account password.

If a tool answers "Authentication failed", this is almost always the cause.

Installing the plugin into Hermes

Option A — from Git (recommended)

hermes plugins install akinfold/hermes-yandex-calendar/hermes_yandex_calendar --enable

Note the /hermes_yandex_calendar at the end. The plugin lives in that directory, not at the repository root, and Hermes reads the manifest from whatever you point it at. Name the directory and the install is a plugin: Hermes prompts for YANDEX_CALENDAR_LOGIN and YANDEX_CALENDAR_APP_PASSWORD, installs under the manifest name yandex_calendar, and --enable enables that name. It also scans only that directory, so the tests and workflows in this repository stay out of the security report.

Point it at the repository root instead and the install still appears to succeed, but it copies a directory with no manifest and no register(ctx) in it: Hermes warns that it "may not be a valid Hermes plugin", asks for nothing, and enables the repository name, which nothing answers to. There is no error to look for: what gives it away is hermes plugins list, which shows the plugin under its real name with not enabled beside it, because --enable wrote the repository name into plugins.enabled and nothing matches it. If you are in that state, remove ~/.hermes/plugins/hermes-yandex-calendar and install again with the directory named — enabling the real name on top of the broken install leaves a stray entry behind.

Option B — pip

pip install hermes-yandex-calendar

Hermes discovers it through the hermes_agent.plugins entry point; add yandex_calendar to plugins.enabled.

Option C — drop-in directory

Download hermes-yandex-calendar-plugin-<version>.zip from the latest release — not the wheel, the .tar.gz, or GitHub's "Source code" archives — and unzip it into ~/.hermes/plugins/ so you end up with ~/.hermes/plugins/yandex_calendar/plugin.yaml, then enable it the same way.

The archive holds the plugin directory alone, with no dependency metadata, so this path installs nothing for you. httpx and defusedxml have to be importable in the environment Hermes runs in: Hermes itself depends on httpx, but defusedxml is not a core Hermes dependency, so if the plugin fails to load with No module named 'defusedxml', run pip install 'defusedxml>=0.7' there. Option B installs both.

Development

python -m venv .venv && source .venv/bin/activate
pip install -e '.[dev]'
ruff check . && ruff format --check .
pytest                       # unit tests, no network

Running the live E2E tests

The e2e-marked tests hit a real Yandex account and are deselected by default. They create, edit, move, and then delete throwaway events 400–402 days out, named with the hermes-e2e prefix (YC_E2E_MARKER overrides it). Most land in the default calendar; the move test also drops a short-lived probe event into your other calendars, one at a time, until it finds one that accepts it, and then moves an event there. Everything is deleted again, so a successful run leaves nothing behind — but the attendees they invite do receive an invitation, so use addresses you own.

Locally

YANDEX_CALENDAR_LOGIN=you@yandex.ru \
YANDEX_CALENDAR_APP_PASSWORD=xxxx \
YC_E2E_ATTENDEES=you+guest@yandex.ru \
pytest -m e2e

YC_E2E_ATTENDEES is the comma-separated list of addresses the throwaway event invites, and each one really is emailed an invitation — so list mailboxes you own. Omit it and the suite falls back to a +e2e sub-address of the account itself, which lands in your own inbox. That fallback needs YANDEX_CALENDAR_LOGIN in full e-mail form (you@yandex.ru); with a bare login there is nothing to derive it from and the round-trip test fails asking for YC_E2E_ATTENDEES. Two constraints, both learned the hard way against the live server:

• The addresses must exist. A made-up one (guest@example.com) bounces back into your mailbox.
• They must not resolve to the account itself. Yandex canonicalises addresses (@ya.ru → @yandex.ru) and drops an attendee that equals the ORGANIZER, so a plain alias of your own login silently disappears and the round-trip check fails. A +tag sub-address is delivered to the same mailbox but stays a distinct attendee.

Or keep all three out of the command line, in ~/.yandex-calendar-login, ~/.yandex-calendar-app-password, and ~/.yandex-calendar-attendees, and just run pytest -m e2e — see tests/e2e/conftest.py.

The suite builds its client exactly as the plugin does, so every YANDEX_CALENDAR_* setting it does not find in the environment (or, for the credentials, in those files) is looked up in ~/.hermes/.env — YANDEX_CALENDAR_BASE_URL and YANDEX_CALENDAR_CALENDARS included. On a machine with Hermes already configured, pytest -m e2e therefore runs against that account instead of skipping.

On GitHub Actions

The E2E (live) workflow is manual (workflow_dispatch). It reads YANDEX_CALENDAR_LOGIN, YANDEX_CALENDAR_APP_PASSWORD, and YC_E2E_ATTENDEES from the secrets of a GitHub Environment named yandex-calendar-e2e. All three must be secrets — the workflow reads nothing from environment variables, so a value defined as a variable arrives empty: without the credentials every test is skipped, and without YC_E2E_ATTENDEES the suite falls back to the +e2e sub-address. The optional install_hermes input also runs pip install hermes-agent beforehand, on a best-effort basis.

Related Hermes plugins

Part of a family of Yandex plugins for Hermes Agent:

• hermes-yandex-disk — browse, read, write, and share files on Yandex Disk (REST API).
• hermes-yandex-mail — search, read, flag, move, and delete Yandex Mail messages over IMAP, and send over SMTP when sending is switched on.
• hermes-yandex-search-api — Yandex web search backend and generative, cited answers for Hermes (Yandex Search API).

Contributing

Issues and PRs are welcome — see CONTRIBUTING.md for the layout, the plugin contract rules worth knowing, and the release process.

License

MIT — see LICENSE.