shift-swap

---
name: shift-swap
description: Checks a staff-arranged shift swap against the same rest and hours limits the original rota was built to, before a manager approves it, because a swap that looks fair between two colleagues can still push one of them under the 11-hour daily rest period, over the 48-hour average, or into a pattern their written statement no longer describes. It also works out when a swap has happened often enough that it is no longer a one-off and needs a written statement of change within the legal time limit. Use whenever a worker asks to swap a shift, cover a colleague, or trade a weekend, and before a manager says yes.
---

# A shift swap that gets checked the same way the rota was

You give this the original rota, the swap being requested, and who is doing which shift instead. You get back the daily and weekly rest check for both workers after the swap, their running 48-hour average after the swap, and a flag if the pattern has repeated enough times to need a written statement of change.

## What it does

1. **Treat the swap as a new rota, not an exception to the old one.** The Working Time Regulations 1998 set the same limits whoever is on the shift: regulation 10(1) still entitles each worker to "a rest period of not less than eleven consecutive hours in each 24-hour period during which he works for his employer", and regulation 4(1) still caps working time at "an average of 48 hours for each seven days" over the applicable reference period. A swap approved on the basis that "it's their own choice" does not change either figure. Recalculate both workers' gaps and averages with the swap in place, not with the original rota.
2. **Check the worker picking up the extra shift first.** The commonest way a swap breaks the rules is the person covering a colleague's weekend also working their own full week either side of it, so their closing shift on Friday and the colleague's opening shift on Saturday sit closer together than 11 hours apart, or their total for the week pushes their running average over 48. Run the daily rest and weekly average check on the covering worker exactly as built in rota-builder, using the swapped shifts in place of the originals.
3. **Check the weekly rest pattern still holds for both workers.** Regulation 11(1) entitles each worker to "an uninterrupted rest period of not less than 24 hours in each seven-day period", or the 14-day alternative the business has chosen under regulation 11(2). A swap that moves someone's day off to cover a colleague can leave them with no qualifying rest period in that window at all, even though each individual shift is fine.
4. **Count how many times this pair has swapped this pattern.** A single one-off swap is not a change to anyone's contract. A pattern that repeats, such as the same two workers permanently trading Tuesday for Saturday every week, is a different working pattern in substance, and section 4(1) of the Employment Rights Act 1996 requires the employer to give a written statement of the change "at the earliest opportunity and, in any event, not later than one month after the change in question." Flag a repeat pattern rather than letting it run as an informal swap indefinitely with no written record.
5. **Record who approved it and when.** A swap with no record of manager sign-off is the thing that gets disputed six weeks later when nobody remembers whether it was agreed, covered, or just happened. Log the date, both workers' names, the shifts exchanged, and the name of the person who approved it.

## Then it checks

1. Both workers' daily rest gaps are recalculated with the swap in place and shown, not assumed from the original rota.
2. Both workers' running 48-hour average is recalculated with the swap in place.
3. Both workers still have a qualifying weekly rest period in the affected week under the pattern the business uses.
4. The number of times this exact pair has swapped this exact pattern in the last 12 weeks is counted and shown.
5. The swap has a recorded approver, a recorded date, and the shifts named on both sides.

Any check fails: name it, redo that step once. Failed twice: say what is wrong and stop.

## Rules
- Public information only.
- Never invent a fact, a number or a quote.
- Anything sent in someone's name says whose name it is.
- Never approve a swap on the strength of "they're both happy with it"; the rest and hours limits apply regardless of consent between the two workers.
- A repeat pattern flagged four or more times in 12 weeks is reported as needing a written statement of change; it is never silently absorbed into the next rota without one.
- Young workers are not covered by this skill; use young-worker-rota, because their rest figures are different under the same Regulations.
- This output is a working document prepared for the owner to check against their own rota and written particulars, and for their adviser to check where a repeated pattern may need a formal contract change. It applies the Working Time Regulations 1998 and the Employment Rights Act 1996 to a draft swap; it is not legal advice and it is not confirmation that the approved swap complies.

## Built from
- The Working Time Regulations 1998, regulation 10, https://www.legislation.gov.uk/uksi/1998/1833/regulation/10, SI 1998/1833, read 3 November 2026: the 11-hour daily rest entitlement recalculated for the swapped shifts, behind steps 1 and 2.
- The Working Time Regulations 1998, regulation 4, https://www.legislation.gov.uk/uksi/1998/1833/regulation/4, SI 1998/1833, read 3 November 2026: the 48-hour average limit recalculated for the swapped shifts, behind steps 1 and 2.
- The Working Time Regulations 1998, regulation 11, https://www.legislation.gov.uk/uksi/1998/1833/regulation/11, SI 1998/1833, read 3 November 2026: the weekly rest entitlement, behind step 3.
- Employment Rights Act 1996, section 4, https://www.legislation.gov.uk/ukpga/1996/18/section/4, Act of Parliament, read 3 November 2026: the one-month time limit for a written statement of a change to particulars, behind step 4.

# shift-swap

## You are given
The original published rota for the affected week(s). The swap request: both workers' names, the shifts being exchanged (date, start time, end time, role), and who requested it. A log of prior swaps between any two workers over the last 12 weeks, if one exists. Each affected worker's current running total against the 48-hour average from the rota-builder output, if available. The weekly rest pattern the business uses: `24-hour weekly` or `48-hour fortnightly` or `two-24-hour-fortnightly`. The name of the manager approving the swap and the date of approval.

## Produce
Write into a `./shift-swap-output/` folder:

1. `swap-request.csv` with columns: `swap_ref`, `request_date`, `worker_a_name`, `worker_a_shift_given_up`, `worker_a_shift_taken_on`, `worker_b_name`, `worker_b_shift_given_up`, `worker_b_shift_taken_on`, `approver_name`, `approval_date`. `swap_ref` is SW0001 upward.
2. `post-swap-rota.csv` with the same columns as `rota-grid.csv` from rota-builder, reflecting the rota with the swap applied.
3. `daily-rest-recheck.csv` with columns: `worker_name`, `date`, `previous_shift_end`, `next_shift_start`, `gap_hours`, `verdict`, `changed_by_swap`. `changed_by_swap` is `yes` or `no`. `verdict` is `pass` or `below 11 hours`.
4. `weekly-average-recheck.csv` with columns: `worker_name`, `reference_period`, `total_hours_after_swap`, `average_hours_per_week_after_swap`, `verdict`. `verdict` is `pass` or `average exceeds 48 hours`.
5. `weekly-rest-recheck.csv` with columns: `worker_name`, `period_start`, `period_end`, `pattern_applied`, `rest_periods_found`, `verdict`. `verdict` is `pass` or `rest period not met`.
6. `repeat-pattern-log.csv` with columns: `worker_a_name`, `worker_b_name`, `pattern_description`, `occurrences_last_12_weeks`, `flagged_for_written_statement`. `flagged_for_written_statement` is `yes` if `occurrences_last_12_weeks` is 4 or more, otherwise `no`.
7. `gaps.md` - a numbered list of: every `below 11 hours` row; every `average exceeds 48 hours` row; every `rest period not met` row; every `flagged_for_written_statement` row with `yes`; any swap request with no recorded approver; and any swap where one worker's post-swap shift data could not be calculated.

## Rules
- Codex counts, matches and recalculates. It never approves or refuses a swap, and it never invents a rest pattern, reference period, or prior swap history not supplied.
- Recalculate every daily-rest and weekly-average figure from the post-swap rota; never carry forward a pre-swap figure unchanged.
- `occurrences_last_12_weeks` counts only swaps logged in the supplied history plus this one; it is never estimated.
- Never suggest an alternative swap, never recommend a third worker to cover instead, and never decide whether a repeat pattern should become a permanent change. Report the count; the owner decides.
- Use British English and DD Month YYYY dates. No em dashes in any file you write.
- Every file ends with this line: this is a working document prepared for the owner to check against their own rota and written particulars, and for their adviser to check where a repeated pattern may need a formal contract change. It applies the Working Time Regulations 1998 and the Employment Rights Act 1996 to a draft swap and is not confirmation that the approved swap complies.

## Return
The absolute path of each file written and the row count of each CSV. Both workers' daily-rest gaps before and after the swap. Both workers' average hours after the swap. The weekly-rest verdict for both workers. The `occurrences_last_12_weeks` count for this pair and whether it is flagged. Whether an approver and date were recorded. The `gaps.md` item count.