A lower introductory price can still break the monthly limit. Compare the confirmed £360 and £358 totals with C’s £324 subscription subtotal, whose missing fees remain unresolved. Synthetic teaching example.
Self-contained SVG source of the static offer comparison diagram. Preserves the reviewed teaching constraints; no active content or live recalculation.
Complete text equivalent of the offer comparison diagram, including assumptions, unresolved terms and scenario limits. Static synthetic example.
Make a start
One step at a time.
4 steps
Start with the synthetic worked example or other non-sensitive inputs. Run one prompt at a time in your chosen AI tool. Replace any bracketed placeholders with the requested material, check each reply, and supply the source or earlier outputs that step needs. Paste them again if the tool lacks that context.
Set up the worked example
Open
Open a chat AI that accepts pasted text and start a new conversation. Keep this guide open beside it. Have a calculator ready to check the sums yourself.
Add the sample
Use the fictional text under ‘The starting point’ (Synthetic input) first. In step 1, replace [paste] with its complete paragraph beginning ‘Requirements:’ and ending ‘mandatory fees.’ In step 2, replace [paste full offers] with the entire text under ‘The starting point’ (Synthetic input), from ‘Synthetic example:’ through ‘unknown.’ This includes the shared terms and missing information, not just the three prices. Send one step prompt at a time in the same chat, checking each reply before continuing. Steps 3 and 4 use the earlier messages; paste their prompts without adding text from ‘The intended result’ (Illustrative output).
Start with the synthetic example, then adapt each prompt to your task.
01
State the decision rules
Choose the comparison period and distinguish recurring monthly charges from one-off fees and the whole-contract budget.
Your starting prompt
From my requirements below, list must-haves, preferences, recurring monthly price limits, total budget and comparison period. State explicitly whether one-off setup fees count toward the monthly limit, the total budget, or both. Do not invent weights or rank providers yet.
REQUIREMENTS:
[paste]
Expect
A list of the decision rules: at least 100 Mbps advertised download speed, a £30 recurring monthly limit, a £360 total limit and a 12-month comparison. Mbps means megabits per second, a measure of data speed. No provider ranking yet.
Check
The one-off setup fee counts toward the £360 total, but not the £30 monthly limit. The speed requirement is advertised speed, not a promise of actual speed.
If it differs
If a rule is missing or changed, point to the exact Requirements sentence and ask for a corrected list before step 2. If the reply asks for requirements you already supplied, check that you replaced [paste] with the actual paragraph.
02
Extract every price period
A low introductory price is only part of the bill. Record how long each rate applies before doing the arithmetic.
Your starting prompt
Compare these offers using the same fields: introductory price and duration, later price and duration, minimum term, mandatory fees, tax, advertised service, availability and cancellation terms. Calculate the cost over my comparison period, showing each multiplication. Mark unstated fields "not stated". Do not present a subtotal with unknown fees as a confirmed total.
OFFERS:
[paste full offers]
Expect
A comparison showing each price period, fee and missing term. A should total £360 and B £358. C has £324 for the subscription alone; its additional fees are still unknown.
Check
On your calculator, check 3 × 24 + 9 × 32 = 360, 12 × 29 + 10 = 358 and 12 × 27 = 324. C’s £324 must not be called its confirmed total including all required fees.
If it differs
If the sums differ, show the relevant offer and ask the AI to list every price period and recalculate. If it treats an unknown fee as zero, ask it to restore ‘not stated’ and leave the all-in total unconfirmed.
03
Apply every requirement visibly
An offer can fit the annual budget while breaking your recurring monthly limit. Keep those judgments separate.
Your starting prompt
For each offer, mark each must-have as met, not met or unconfirmed, with evidence. Check every price period against the monthly limit and the complete total against the overall budget. Recommend the best fit only among offers whose required terms are confirmed. Explain whether the headline-price ranking differs from the full-cost ranking.
Expect
Each offer is marked against each requirement. B, Lantern Connect, is the only offer with every supplied first-year price requirement confirmed. A fails the monthly limit in months 4–12; C’s full cost remains unconfirmed.
Check
A’s £360 annual total does not erase its £32 later monthly price. B costs £2 less than A. C cannot be declared the cheapest complete offer while its mandatory fees are missing.
If it differs
If the recommendation ignores a limit or missing fee, name that issue and ask for the requirement-by-requirement comparison again. Keep unknown terms unconfirmed; do not choose a winner by assuming them.
04
Verify before committing
Recheck calculations and ask about material unknown terms. A written comparison is not an instruction to switch.
Your starting prompt
Audit the comparison against the offers. Recalculate introductory periods, later periods, one-off fees and price differences. Flag any unsupported actual-speed guarantee, installation date, renewal price or cancellation claim. List unresolved terms and any existing-provider costs that could change the choice. Do not contact providers, sign up or switch services.
Expect
A checked comparison plus questions about actual speed, installation timing, price after month 12, early cancellation and any cost of leaving the current provider.
Check
Compare the final answer with the original offers and the guide’s worked-example checks. No actual-speed guarantee, installation date, renewal price or cancellation amount is supplied. The result is still a written comparison.
If it differs
If the audit supplies an unsupported fact, quote the sentence and ask for it to be removed or marked unknown. Recheck any changed total with your calculator. Leave unresolved terms as questions before making a separate purchase or switching decision.
Optional: improve the result
See what would change the decision
Use a break-even check for missing fees, then revisit the comparison when you have verified answers.
Advanced prompt
Using only the verified comparison, calculate how much room each incomplete offer has under my total budget. State which missing fee or price fact could change the ranking, and whether any recurring fees could break the monthly limit. Do not assume a fee is zero or predict future pricing. Revise the recommendation only after I supply confirmed terms.
VERIFIED COMPARISON:
[paste]
Optional: use your own input+
Compare your own offers
Start a new chat. Use offer text you are allowed to share, with names, addresses, account numbers and other private details removed. Fill the placeholders below. After checking the rules summary, send these messages one at a time in that chat, checking each reply: “Compare every offer by price period, term, required fees, tax, service, availability and cancellation. Show each multiplication over my comparison period. Keep missing fees unconfirmed.” “Mark every requirement met, not met or unconfirmed for each offer, with evidence. Recommend only from offers whose required terms are confirmed. Compare the headline-price and full-cost rankings.” “Audit against my original requirements and offers. Recalculate costs and price differences. Remove unsupported claims and list unresolved terms.” Check the sums with your calculator. The original advanced extension is sample-only unless adapted to your own checked comparison and limits.
Your own-input prompt
Help me compare ordinary household offers using only the text below. First summarize my must-haves, preferences, comparison period, recurring charge limits and all-in budget. State how one-off fees count. List information you still need; do not invent weights, fees, terms or a recommendation. In later messages, we will extract each price period and fee, calculate costs, apply every requirement and audit the result. Keep missing costs unconfirmed. Return written text only; do not contact anyone, sign up, purchase, switch services or change an account.
MY REQUIREMENTS AND COMPARISON PERIOD
[Paste your requirements, period, limits and treatment of one-off fees.]
COMPLETE OFFER TEXT
[Paste each offer under a distinct label, including price changes, fees, taxes, term and any stated restrictions. Mark missing details as not supplied.]
Check your own result
Every price period is covered once, and the calculations use your comparison period rather than the sample’s figures.
Known mandatory fees count where your rules say they should; an unstated fee is not treated as zero.
Recurring limits, all-in budget and other must-haves are checked separately for each offer.
Any recommendation relies on confirmed required terms; missing terms stay visible as questions.
Show, then try
See the shape of the result.
This input is synthetic. The output is a written illustration of the intended result, not a verified AI-tool run.
01 / The starting point
Synthetic input
Synthetic example: three fictional home-broadband offers. These are invented teaching fixtures, not available deals.
Requirements: at least 100 Mbps advertised download speed; no recurring monthly charge above £30 during the first 12 months, excluding one-off setup charges; no more than £360 total for those 12 months, including setup and any other mandatory fees.
All three quotes list 100 Mbps advertised download speed, a 12-month minimum term and service availability at the supplied address. Actual speeds are not guaranteed. The quoted monthly prices are fixed for the periods stated below.
Offer A, Pebble Broadband: £24 per month for months 1–3, then £32 per month for months 4–12; setup £0; tax included; no other mandatory fees.
Offer B, Lantern Connect: £29 per month for months 1–12; setup £10; tax included; no other mandatory fees.
Offer C, Willow Net: £27 per month for months 1–12, tax included; setup charge and other mandatory fees not stated.
None of the offers states the price after month 12, installation timing or early-cancellation terms. Any cancellation charge from an existing provider is unknown.
Copies text only. For image or file tasks, use the source files named in the steps too.
COMPARISON: FIRST 12 MONTHS
Pebble Broadband
- Headline price: £24 per month for the first three months.
- Later price: £32 per month for the next nine months.
- Confirmed total: (3 × £24) + (9 × £32) + £0 setup = £360.
- Total budget: met. Recurring monthly limit: not met in months 4–12.
Lantern Connect
- Price: £29 per month for all 12 months.
- Confirmed total: (12 × £29) + £10 setup = £358.
- Total budget: met. Recurring monthly limit: met.
Willow Net
- Price: £27 per month for all 12 months.
- Known subscription subtotal: 12 × £27 = £324.
- All-in total: unconfirmed because setup and other mandatory fees are missing.
- Monthly subscription limit: met. Full budget: unconfirmed.
SPEED AND TERM
All three list 100 Mbps and a 12-month minimum term. That meets the advertised-speed requirement; it does not establish the actual speed the household will receive.
DECISION
Lantern Connect is the only offer that confirms every supplied first-year price requirement. Its £358 total is £2 below Pebble Broadband's £360, despite Pebble's lower introductory price.
Willow Net could cost less, but its missing fees prevent an all-in comparison. Mandatory fees would need to total no more than £36 to fit the £360 annual budget; any recurring fees would also need to fit the £30 monthly limit.
BEFORE SWITCHING
Confirm installation timing, actual speed information, early-cancellation terms and the price after month 12. Check any charge for leaving the current provider. This comparison does not authorize a purchase or switch.
These checks use the worked example and its particular facts. With your own material, check your actual names, numbers, sources and rules; do not reuse the sample’s values as the answer.
Unsaved checks stay in this tab and reset when you reload. If you choose Save guide, its current example checkmarks are kept in this browser when storage is available.
!
A few things to watch for.
Multiplying the introductory price by the whole contract length.
Calling an offer cheapest when setup charges, mandatory fees or later prices are missing.
What has been checked?
Documentation
No dated source review recorded.
Included files
Scoped checks passed on 2026-10-14. Fixture checks. See scope below.
AI workflow
Not run in a recorded consumer-AI workflow.
Time savings
Time savings not measured
Read the scope and evidence
offer-comparison-diagram-v1.png
2026-10-14 · semantic fixture · passed
Direct editorial inspection of the actual accepted raster and byte identity to that reviewed file, with supplied synthetic values reconciled to fresh local arithmetic. This check does not establish integrated browser rendering, user accessibility, AI performance or real-world plan reliability.
Accepted raster retained byte-for-byte; intrinsic dimensions 780 × 2816; actual image opened and inspected.
C: £324 known subscription subtotal; all-in monthly compliance and total remain separately unconfirmed.
C fee headroom is £3 recurring per month and £36 for all mandatory fees across the year, simultaneous bounds.
Environment: Local Linux; arithmetic and exhaustive synthetic schedule enumeration, static SVG text/structure and SHA-256 checks, PNG verification, and direct visual inspection of the accepted PNG. No browser, consumer AI, real booking or physical trial.
Static SVG elements/attributes and visible text inspected; exact accepted bytes retained and supplied synthetic values reconciled to local arithmetic. This is a static fixture/source check, not a browser, physical trial or consumer-AI execution.
Accepted SVG retained byte-for-byte; 390 × 1408 viewBox; static allowlisted elements and no external references, events or active content.
C: £324 known subscription subtotal; all-in monthly compliance and total remain separately unconfirmed.
C fee headroom is £3 recurring per month and £36 for all mandatory fees across the year, simultaneous bounds.
Environment: Local Linux; arithmetic and exhaustive synthetic schedule enumeration, static SVG text/structure and SHA-256 checks, PNG verification, and direct visual inspection of the accepted PNG. No browser, consumer AI, real booking or physical trial.
Text equivalent preserves every substantive source line; only the source-hash line, internal revision footnote and heading revision suffix were removed. Supplied synthetic values and limits reconciled to local arithmetic; no live execution or plan-reliability claim.
Exact three-part text delta recorded; all substantive lines, constraints, unknowns and limits retained.
C: £324 known subscription subtotal; all-in monthly compliance and total remain separately unconfirmed.
C fee headroom is £3 recurring per month and £36 for all mandatory fees across the year, simultaneous bounds.
Environment: Local Linux; arithmetic and exhaustive synthetic schedule enumeration, static SVG text/structure and SHA-256 checks, PNG verification, and direct visual inspection of the accepted PNG. No browser, consumer AI, real booking or physical trial.
