when-free

Someone asks when you're free. This reads your calendar and gives you the answer, ready to paste.

• Paste the message, get the slots. It reads "Tuesday or Wednesday next week, between 10am and 4pm" and answers for exactly those days and hours.
• Works with Google, Outlook and iCloud calendars, or any .ics file. Several calendars at once.
• Private. It runs on your computer, needs no account and no API key, and never changes your calendar.
• Works from your AI tools too: Claude, Cursor and other MCP clients, Open WebUI, n8n, Shortcuts, scripts.
• And on your other devices: phones, tablets and watches, Home Assistant (and Alexa, Google Home, Siri through it), and the menu bar or status bar of macOS, Linux and Windows.

Contents

Try it · Add your calendar · Everyday use · Reading a message · Use it from other tools · Other devices · Privacy · Settings · What counts as busy · Limits · Problems

Try it in a minute

With uv, nothing to install first:

uvx when-free demo

To keep it (needs Python 3.11 or newer):

uv tool install when-free          # or: pipx install when-free
whenfree demo

Using Claude Desktop? You can skip all of this: install the one-click extension.

whenfree demo makes up a calendar for next week and answers a recruiter's message from it. It reads none of your data and saves nothing:

  > Hi! Thanks for applying. Could you share a few times on Tuesday, Wednesday or Thursday next week,
  > between 10am and 4pm? The interview takes about an hour.

  Free between 10:00 and 16:00 (Europe/London), slots of 60+ minutes, 15-minute buffer around events:
  - Tue 13 Oct: 11:45–12:45, 14:15–16:00
  - Wed 14 Oct: 12:15–14:15
  - Thu 15 Oct: 13:15–14:45

Add your calendar

1. Copy your calendar's private address. It's a link that ends in .ics:

   Calendar	Where to find it
   Google Calendar	Settings → click your calendar on the left → Integrate calendar → Secret address in iCal format
   Outlook	Settings → Calendar → Shared calendars → Publish a calendar → the ICS link
   iCloud	Calendar → the share icon next to the calendar → Public Calendar (a webcal:// link is fine)
   Anything else	Any .ics link, or an exported .ics file

2. Run whenfree add and paste it. The address isn't shown while you paste. It's checked first, and saved only if it works:

   consoleCopy

   $ whenfree add
   Paste the address and press Enter (it is not shown):
   Added 'personal': 412 events, 9 block time in the next 14 days.
   Saved in /Users/you/.config/when-free/config.toml, readable only by you. Now run: whenfree
   

3. Run whenfree. You'll see your free time for the next working days.

On a Mac, pbpaste | whenfree add takes the address straight from the clipboard.

Keep the address secret. It works like a password: anyone who has it can read that calendar. Give it to whenfree add and to nothing else, so not to a chat, a shell command or a repository. If it leaks, reset it in your calendar's settings.

whenfree add --name work                 # a second calendar: asks for its address
whenfree add ~/calendars/family.ics      # an exported file instead of an address
whenfree check                           # can every calendar be read?

Everyday use

Only the slot lines go to standard output. The context goes to standard error, so | pbcopy copies exactly what you'd paste into a reply.

Reading a message

--message finds the days and hours in ordinary text. It understands:

• Dates written in any common way: Thu 1 Oct · Thursday the 1st of October · Monday, October 5th · 5 October · 2026-10-05 · Wednesday 30th
• Hours: between 10:00am and 4:00pm · 10:00–16:00 · 9-5pm · 2 to 4 pm
• Words, when there's no date (here, today is Thursday 1 Oct):

It always tells you how it read the dates, so you can check them against the message. A few rules keep it from guessing:

• Explicit dates win. A heading like "Next week:" above "Wednesday 30th, Thursday 1st" doesn't add a whole week.
• "Good morning" is a greeting, not a time.
• Days already past are left out and named, never dropped silently. "Wednesday 30th" means the nearest Wednesday that's a 30th, so a message from last week reads as last week.
• Words count from today. For an older message that says "tomorrow", give the days yourself with --days.

when-free never connects to your mailbox. You paste the message, pipe it in, or save it to a file.

[extract]
command = ["ollama", "run", "llama3.2"]          # the prompt is sent on standard input
# command = ["my-cli", "ask", "{prompt}"]        # or placed where {prompt} is

Use it from other tools

Every way gives the same answer, only reads, and leaves event titles out unless asked.

Claude Code plugin

The plugin bundles the MCP server with a skill that tells Claude when to use it: when you ask about your availability, paste a message asking when you can meet, or before it proposes a time.

/plugin marketplace add YauhenBichel/when-free
/plugin install when-free@when-free

Then add your calendar once, if you have not yet: uvx when-free add.

MCP: Claude, Cursor and other assistants

claude mcp add when-free -- uvx when-free mcp          # Claude Code

For Cursor and other MCP clients, add this to their server list. uvx fetches when-free the first time, so there's nothing to install:

{
  "mcpServers": {
    "when-free": { "command": "uvx", "args": ["when-free", "mcp"] }
  }
}

If you installed it with uv tool install, use "command": "whenfree", "args": ["mcp"] instead. It's also listed in the MCP registry as io.github.YauhenBichel/when-free.

Then just ask: "Here's the recruiter's message. Which of those times can I do?" The assistant calls free_slots and answers from your real calendar.

If a tool can't do its job, the assistant gets an error it can read ("could not read the calendar 'work'"), never a guess.

HTTP: Open WebUI, n8n, Shortcuts and scripts

whenfree serve                    # http://127.0.0.1:8765, only reachable from this computer

curl -H "Authorization: Bearer $(cat ~/.config/when-free/token)" \
  'http://127.0.0.1:8765/free_slots?days=next%20week&hours=afternoon'

• POST /free_slots with a JSON body, or GET with a query string. Same for /check_calendars.
• The answer is {"ok": true, "text": "...", "data": {...}}, or {"ok": false, "error": "..."} with status 400.
• OpenAPI description at /openapi.json. To set up Open WebUI, n8n or Shortcuts, see the recipes.
• The token is created on first run and kept in ~/.config/when-free/token, readable only by you. Or set your own with WHENFREE_TOKEN. Every tool call needs it.
• Requests addressed to any host other than this computer are refused. A web page may call it only from an origin you allow: whenfree serve --allow-origin http://localhost:3000. With --host 0.0.0.0 it's reachable from your network, and the token alone protects it, so use that only on a network you trust.

Function-calling harnesses

whenfree schema                    # the tool definitions: name, description, inputSchema
whenfree schema --format openai    # the same, as {"type": "function", "function": {...}}
whenfree call free_slots --args '{"days": "next week", "hours": "10:00-16:00"}'

whenfree call prints {"ok": true, "text": "...", "data": {...}}, or {"ok": false, "error": "..."} with exit code 1. Arguments can also come on standard input.

Python

from whenfree import api

result = api.find_free(api.Query(days="next week", hours="10:00-16:00", min_minutes=45))
for day in result["days"]:
    print(day["label"], day["free"])          # for example: Mon 12 Oct [['10:00', '11:45'], ['13:15', '16:00']]

find_free returns plain dicts and lists, ready for json.dumps, and raises api.Problem with a message that's safe to show. Pass reader= to supply calendar text yourself instead of fetching it.

On your other devices

$ whenfree now
Busy until 15:30 · next free 15:45–17:00

Devices see whether you're free and your free slots, never event titles. Each phone has its own token that you can revoke, and an unreadable calendar shows as "unknown", never "free".

Privacy

• It runs on your computer. It fetches your calendar feeds and nothing else. It never writes to a calendar and never sends a message.
• Your calendar address stays secret. It's never printed, isn't shown while you paste it, and is stored in a file only you can read. Errors name the calendar ("personal"), never its address.
• Assistants see free time, not your events. Event titles are left out unless the assistant asks with include_busy, and that option's description tells the model that titles are private. No tool can add, change or delete anything, and no tool takes a calendar address, which goes from you to whenfree add only.

Settings

All optional except a calendar. They live in ~/.config/when-free/config.toml, and command-line flags win over the file.

What counts as busy

A slot shorter than min_minutes after the buffers isn't offered. For today, the day starts at the next quarter hour, not in the past.

Limits

• It reads; it doesn't book. It never writes to a calendar and never sends a message.
• It's as fresh as the feed. Google refreshes the secret address with some delay, so an event added a minute ago may be missing. Run whenfree --busy to see what it saw.
• Every calendar or none. If one calendar can't be read, no slots are shown, because busy time would look free.
• Repeating events. Daily, weekly, monthly (by date, or "first Monday", "last Friday") and yearly rules are expanded, with intervals, end dates, counts, skipped dates and moved occurrences. Rarer rules (BYSETPOS, week numbers) aren't. For those the first date is blocked and a note says so.
• Time zones come from the events. A zone name the time zone database doesn't know (some Outlook exports) is read in your own zone.

If something does not work

Development

uv run --with pytest pytest -q        # a few seconds; no network

The tests use a small calendar in tests/data/sample.ics and a fixed clock (WHENFREE_NOW). The code is grouped by component:

tests/test_structure.py fails if a component imports one it may not, so the domain stays free of front ends.

See CONTRIBUTING.md.

Licence

Apache-2.0.