tilwhen date engine

by tilwhen.com · remote · no sign-in to list tools · v1.0.1 · published by com.tilwhen

Deterministic date arithmetic with auditable receipts: business days, due dates, holidays.

Final · 3Changes · 5

Compare Registry entry

9 tools: 3 do something that can't be undone, 5 change things and 1 only read.

Scanned Oct 21, 2026

Deletes or cancels0Claude Code: deny
Can't be undone3Claude Code: ask: see these tools
Changes things5Claude Code: ask: see these tools
Only reads1Claude Code: allow: see these tools

4 checks matched something in the tool definitions. No finding is not a safety guarantee. How the checks work.

claude mcp add --transport http tilwhen https://mcp.tilwhen.com/mcp

Findings

Matches of fixed checks, with the text they matched.

4 warn

Warnadd_days
The server marks "add_days" read-only (readOnlyHint: true), and its own name, description or input give the class "write".
Matched text
annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The name "add_days" says "add": a word for a change.
What this check looks for
Warndays_between
The server marks "days_between" read-only (readOnlyHint: true), and its own name, description or input give the class "irreversible".
Matched text
annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The input addresses people (input.to): what it sends cannot be taken back.
What this check looks for
Warnbusiness_days
The server marks "business_days" read-only (readOnlyHint: true), and its own name, description or input give the class "irreversible".
Matched text
annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The input addresses people (input.to): what it sends cannot be taken back.
What this check looks for
Warnexplain
The server marks "explain" read-only (readOnlyHint: true), and its own name, description or input give the class "irreversible".
Matched text
annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The name "explain" says "explain": a word for reading.
What this check looks for

Tools

Open a tool for its reasons and full description. Descriptions are the publisher's own words, shown as they are.

9 tools

Can't be undone 3Sends, pays, publishes or merges: once done, it cannot be taken back.Claude Code: ask

business_daysSpan mode (from+to): business days between two dates, exclusive of the start day, inclusive of the end day.1 finding
Why it is in this group
- The input addresses people (input.to): what it sends cannot be taken back.
- The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
Findings
- Warn
  The server marks "business_days" read-only (readOnlyHint: true), and its own name, description or input give the class "irreversible".
  Matched text
  annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The input addresses people (input.to): what it sends cannot be taken back.
  What this check looks for
Description, as the server wrote it
Span mode (from+to): business days between two dates, exclusive of the start day, inclusive of the end day. Add mode (days, optional date): the date N business days away. Passing from or to selects span mode and needs both; days and date are then ignored, so add mode takes its start date in date, not from. Optional holiday jurisdiction or custom calendar, and a selectable working week. For calendar days use add_days, subtract_days or days_between.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false
days_betweenSigned whole calendar days from the from date to the to date, midnight to midnight in tz: positive when to is later, negative when it is earlier.1 finding
Why it is in this group
- The input addresses people (input.to): what it sends cannot be taken back.
- The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
Findings
- Warn
  The server marks "days_between" read-only (readOnlyHint: true), and its own name, description or input give the class "irreversible".
  Matched text
  annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The input addresses people (input.to): what it sends cannot be taken back.
  What this check looks for
Description, as the server wrote it
Signed whole calendar days from the from date to the to date, midnight to midnight in tz: positive when to is later, negative when it is earlier. Endpoints are exclusive, so this is the gap and consecutive dates are 1 apart. Either date may be "today", resolved in tz. For working days between two dates use business_days; to move a date by N days use add_days or subtract_days.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false
explainRuns any operation and returns the receipt plus human-readable derivation steps.1 finding
Why it is in this group
- The name "explain" says "explain": a word for reading.
- The description's first verb is "run": a word for a change.
- The input addresses people (input.to): what it sends cannot be taken back.
- The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
Findings
- Warn
  The server marks "explain" read-only (readOnlyHint: true), and its own name, description or input give the class "irreversible".
  Matched text
  annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The name "explain" says "explain": a word for reading.
  What this check looks for
Description, as the server wrote it
Runs any operation and returns the receipt plus human-readable derivation steps. Set op, then pass the fields that operation's own tool takes. Use it when the user asks how an answer was reached.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false

Changes things 5Creates or changes something that can be changed back.Claude Code: ask

add_daysThe date N whole calendar days after a date (exclusive counting: the start date is day 0).1 finding
Why it is in this group
- The name "add_days" says "add": a word for a change.
- The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
Findings
- Warn
  The server marks "add_days" read-only (readOnlyHint: true), and its own name, description or input give the class "write".
  Matched text
  annotations: {"readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}; The name "add_days" says "add": a word for a change.
  What this check looks for
Description, as the server wrote it
The date N whole calendar days after a date (exclusive counting: the start date is day 0). Omit date for today in tz. For working days use business_days; for the gap between two dates use days_between.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false
holidaysObserved public holidays with the nominal (legal) date and status: rule (statutory) or declared (officially declared for that year).No findings
Why it is in this group
- Nothing in its name or description says what it does, so it is counted as a write.
- The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
Description, as the server wrote it
Observed public holidays with the nominal (legal) date and status: rule (statutory) or declared (officially declared for that year). Declared-only holidays are omitted for undeclared years, with a holiday_data_incomplete warning.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false
invoice_dueDue date for Net-N payment terms (calendar days, invoice date = day 0).No findings
Why it is in this group
- Nothing in its name or description says what it does, so it is counted as a write.
- The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
Description, as the server wrote it
Due date for Net-N payment terms (calendar days, invoice date = day 0). Optional roll-forward past weekends and, with a jurisdiction or custom calendar, public holidays.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false
next_occurrenceThe next occurrence strictly after the base date (default today) of either a tracked event slug (e.g.No findings
Why it is in this group
- Nothing in its name or description says what it does, so it is counted as a write.
- The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
Description, as the server wrote it
The next occurrence strictly after the base date (default today) of either a tracked event slug (e.g. "christmas") or a weekday (0 = Sunday .. 6 = Saturday). Provide exactly one of event/weekday.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false
subtract_daysThe date N whole calendar days before a date (exclusive counting: the start date is day 0).No findings
Why it is in this group
- Nothing in its name or description says what it does, so it is counted as a write.
- The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
Description, as the server wrote it
The date N whole calendar days before a date (exclusive counting: the start date is day 0). Omit date for today in tz. For working days use business_days; for the gap between two dates use days_between.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false

Only reads 1Looks things up and changes nothing.Claude Code: allow

parse_date_queryParses queries like "90 business days from today in uganda" into a normalized operation, answers it, and returns the auditable receipt.No findings
Why it is in this group
- The name "parse_date_query" says "query": a word for reading.
Description, as the server wrote it
Parses queries like "90 business days from today in uganda" into a normalized operation, answers it, and returns the auditable receipt. Ambiguous dates (03/04/2027) return needsClarification instead of a guess.
Annotations the server declares
- readOnlyHint: true
- idempotentHint: true
- openWorldHint: false
- destructiveHint: false

This is not a safety rating, and no finding is not a safety guarantee. The groups and findings come from fixed checks of the tool definitions the server returned on the date shown, not from its code or what it does when called. How the checks work.

Install

Pinned to version 1.0.1. Values in angle brackets are yours to fill in.

claude mcp add --transport http tilwhen https://mcp.tilwhen.com/mcp

Run in a terminal.

Claude Code permissions

Allow the reads, ask before a change, deny the deletes. Paste into .claude/settings.json.

.claude/settings.json

{
  "permissions": {
    "allow": [
      "mcp__tilwhen__parse_date_query"
    ],
    "ask": [
      "mcp__tilwhen__add_days",
      "mcp__tilwhen__subtract_days",
      "mcp__tilwhen__days_between",
      "mcp__tilwhen__business_days",
      "mcp__tilwhen__invoice_due",
      "mcp__tilwhen__next_occurrence",
      "mcp__tilwhen__holidays",
      "mcp__tilwhen__explain"
    ],
    "deny": []
  }
}

Tools that only read are allowed, tools that change things ask first, tools that delete or cancel are denied. It assumes the server is installed as tilwhen. Review it before you use it.

Keep track

Get told when this server's tools change: a new tool, a new description, a new class.

https://anlyon.dev/servers/com.tilwhen/tilwhen/changes.xml

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Source: MCP Registry. Synced Oct 21, 2026, 18:07 UTC.

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