Understand the failure.
Verify the repair.
Small, reproducible software failures. The broken implementation, the fix that didn’t work, and the one that passed—preserved together.
Explore the cases ↓How results are verified ↗WHAT THE ARCHIVE CONTAINS
100840 executable cases. 20168 are open.
Every case records the implementation that fails, the fix that did not work, and the repair that passed its checks—with recorded outputs and source hashes. This release adds 100840 cases across 20168 failure mechanisms and 254 domains.
The open tier gives you the failure and the unsuccessful fix for one case in every mechanism. The remaining 80672 cases, 5 variants per mechanism, are member-only: the verified repair, its recorded checks, and the full fixture suite are held in the member archive. Read the methodology ↗
A RECORD OF WHAT WENT WRONG
Browse the archive / 100840
Surcharges are not charged on zero-rate slices · case 01
Additional-dwelling purchases under 250000 pay no surcharge.
Surcharges are not charged on zero-rate slices · case 02
Additional-dwelling purchases under 250000 pay no surcharge.
Surcharges are not charged on zero-rate slices · case 03
Additional-dwelling purchases under 250000 pay no surcharge.
Surcharges are not charged on zero-rate slices · case 04
Additional-dwelling purchases under 250000 pay no surcharge.
Surcharges are not charged on zero-rate slices · case 05
Additional-dwelling purchases under 250000 pay no surcharge.
The liability is rounded to the nearest pound instead of down · case 01
Some liabilities are one pound higher than stipulated.
The liability is rounded to the nearest pound instead of down · case 02
Some liabilities are one pound higher than stipulated.
The liability is rounded to the nearest pound instead of down · case 03
Some liabilities are one pound higher than stipulated.
The liability is rounded to the nearest pound instead of down · case 04
Some liabilities are one pound higher than stipulated.
The liability is rounded to the nearest pound instead of down · case 05
Some liabilities are one pound higher than stipulated.
First-time-buyer relief is granted on an additional dwelling · case 01
A buyer flagged as both first-time and additional-dwelling gets relief plus a surcharge on relief slices.
First-time-buyer relief is granted on an additional dwelling · case 02
A buyer flagged as both first-time and additional-dwelling gets relief plus a surcharge on relief slices.
First-time-buyer relief is granted on an additional dwelling · case 03
A buyer flagged as both first-time and additional-dwelling gets relief plus a surcharge on relief slices.
First-time-buyer relief is granted on an additional dwelling · case 04
A buyer flagged as both first-time and additional-dwelling gets relief plus a surcharge on relief slices.
First-time-buyer relief is granted on an additional dwelling · case 05
A buyer flagged as both first-time and additional-dwelling gets relief plus a surcharge on relief slices.
Only the larger surcharge applies to a non-resident additional dwelling · case 01
Non-resident second-home buyers pay 3 surcharge points instead of 5.
Only the larger surcharge applies to a non-resident additional dwelling · case 02
Non-resident second-home buyers pay 3 surcharge points instead of 5.
Only the larger surcharge applies to a non-resident additional dwelling · case 03
Non-resident second-home buyers pay 3 surcharge points instead of 5.
Only the larger surcharge applies to a non-resident additional dwelling · case 04
Non-resident second-home buyers pay 3 surcharge points instead of 5.
Only the larger surcharge applies to a non-resident additional dwelling · case 05
Non-resident second-home buyers pay 3 surcharge points instead of 5.
The tax on the per-part quotient is not multiplied back by the parts · case 01
A couple's tax is roughly halved.
The tax on the per-part quotient is not multiplied back by the parts · case 02
A couple's tax is roughly halved.
The tax on the per-part quotient is not multiplied back by the parts · case 03
A couple's tax is roughly halved.
The tax on the per-part quotient is not multiplied back by the parts · case 04
A couple's tax is roughly halved.
The tax on the per-part quotient is not multiplied back by the parts · case 05
A couple's tax is roughly halved.
The half-part benefit cap lowers tax instead of limiting the benefit · case 01
Families with extra parts pay less than the capped amount.
The half-part benefit cap lowers tax instead of limiting the benefit · case 02
Families with extra parts pay less than the capped amount.
The half-part benefit cap lowers tax instead of limiting the benefit · case 03
Families with extra parts pay less than the capped amount.
The half-part benefit cap lowers tax instead of limiting the benefit · case 04
Families with extra parts pay less than the capped amount.
The half-part benefit cap lowers tax instead of limiting the benefit · case 05
Families with extra parts pay less than the capped amount.
The benefit cap is applied per extra part instead of per extra half-part · case 01
Each child's half-part is capped at half the stipulated amount.
The benefit cap is applied per extra part instead of per extra half-part · case 02
Each child's half-part is capped at half the stipulated amount.
The benefit cap is applied per extra part instead of per extra half-part · case 03
Each child's half-part is capped at half the stipulated amount.
The benefit cap is applied per extra part instead of per extra half-part · case 04
Each child's half-part is capped at half the stipulated amount.
The benefit cap is applied per extra part instead of per extra half-part · case 05
Each child's half-part is capped at half the stipulated amount.
A couple declared with a single part is accepted · case 01
A couple with 1.5 parts gets a negative extra-part count that raises the capped tax.
A couple declared with a single part is accepted · case 02
A couple with 1.5 parts gets a negative extra-part count that raises the capped tax.
A couple declared with a single part is accepted · case 03
A couple with 1.5 parts gets a negative extra-part count that raises the capped tax.
A couple declared with a single part is accepted · case 04
A couple with 1.5 parts gets a negative extra-part count that raises the capped tax.
A couple declared with a single part is accepted · case 05
A couple with 1.5 parts gets a negative extra-part count that raises the capped tax.
Carryforwards are consumed newest first · case 01
Old losses expire unused while recent losses are absorbed.
Carryforwards are consumed newest first · case 02
Old losses expire unused while recent losses are absorbed.
Carryforwards are consumed newest first · case 03
Old losses expire unused while recent losses are absorbed.
Carryforwards are consumed newest first · case 04
Old losses expire unused while recent losses are absorbed.
Carryforwards are consumed newest first · case 05
Old losses expire unused while recent losses are absorbed.
Carryforwards offset the whole year's income · case 01
Taxable income drops to zero in a year after a large loss.
Carryforwards offset the whole year's income · case 02
Taxable income drops to zero in a year after a large loss.
Carryforwards offset the whole year's income · case 03
Taxable income drops to zero in a year after a large loss.
Carryforwards offset the whole year's income · case 04
Taxable income drops to zero in a year after a large loss.
Carryforwards offset the whole year's income · case 05
Taxable income drops to zero in a year after a large loss.
A carryforward expires one year early · case 01
A loss is unusable in its final permitted year.
A carryforward expires one year early · case 02
A loss is unusable in its final permitted year.
A carryforward expires one year early · case 03
A loss is unusable in its final permitted year.
A carryforward expires one year early · case 04
A loss is unusable in its final permitted year.
A carryforward expires one year early · case 05
A loss is unusable in its final permitted year.
The 80% limit is rounded to the nearest unit · case 01
In some years one extra unit of carryforward is used.
The 80% limit is rounded to the nearest unit · case 02
In some years one extra unit of carryforward is used.
The 80% limit is rounded to the nearest unit · case 03
In some years one extra unit of carryforward is used.
The 80% limit is rounded to the nearest unit · case 04
In some years one extra unit of carryforward is used.
The 80% limit is rounded to the nearest unit · case 05
In some years one extra unit of carryforward is used.
Fully used and expired carryforwards remain in the report · case 01
The carryforward schedule lists zero balances and long-expired losses.
Fully used and expired carryforwards remain in the report · case 02
The carryforward schedule lists zero balances and long-expired losses.
Fully used and expired carryforwards remain in the report · case 03
The carryforward schedule lists zero balances and long-expired losses.
Fully used and expired carryforwards remain in the report · case 04
The carryforward schedule lists zero balances and long-expired losses.
Fully used and expired carryforwards remain in the report · case 05
The carryforward schedule lists zero balances and long-expired losses.
Lifetime gifts are left out of the tentative tax base · case 01
An estate after large gifts is taxed in lower brackets than the cumulative transfers warrant.
Lifetime gifts are left out of the tentative tax base · case 02
An estate after large gifts is taxed in lower brackets than the cumulative transfers warrant.
Lifetime gifts are left out of the tentative tax base · case 03
An estate after large gifts is taxed in lower brackets than the cumulative transfers warrant.
Lifetime gifts are left out of the tentative tax base · case 04
An estate after large gifts is taxed in lower brackets than the cumulative transfers warrant.
Lifetime gifts are left out of the tentative tax base · case 05
An estate after large gifts is taxed in lower brackets than the cumulative transfers warrant.
The exclusion amount is subtracted from the tax as if it were a credit · case 01
Estates owe no tax far above the exclusion because 13.6 million of tax is forgiven.
The exclusion amount is subtracted from the tax as if it were a credit · case 02
Estates owe no tax far above the exclusion because 13.6 million of tax is forgiven.
The exclusion amount is subtracted from the tax as if it were a credit · case 03
Estates owe no tax far above the exclusion because 13.6 million of tax is forgiven.
The exclusion amount is subtracted from the tax as if it were a credit · case 04
Estates owe no tax far above the exclusion because 13.6 million of tax is forgiven.
The exclusion amount is subtracted from the tax as if it were a credit · case 05
Estates owe no tax far above the exclusion because 13.6 million of tax is forgiven.
The deceased spouse's unused exclusion is ignored · case 01
A surviving spouse's estate pays tax as if no exclusion had been ported.
The deceased spouse's unused exclusion is ignored · case 02
A surviving spouse's estate pays tax as if no exclusion had been ported.
The deceased spouse's unused exclusion is ignored · case 03
A surviving spouse's estate pays tax as if no exclusion had been ported.
The deceased spouse's unused exclusion is ignored · case 04
A surviving spouse's estate pays tax as if no exclusion had been ported.
The deceased spouse's unused exclusion is ignored · case 05
A surviving spouse's estate pays tax as if no exclusion had been ported.
Prior gifts below the exclusion produce a negative gift credit · case 01
Estates with modest prior gifts are charged extra tax.
Prior gifts below the exclusion produce a negative gift credit · case 02
Estates with modest prior gifts are charged extra tax.
Prior gifts below the exclusion produce a negative gift credit · case 03
Estates with modest prior gifts are charged extra tax.
Prior gifts below the exclusion produce a negative gift credit · case 04
Estates with modest prior gifts are charged extra tax.
Prior gifts below the exclusion produce a negative gift credit · case 05
Estates with modest prior gifts are charged extra tax.
The local surtax is computed on state tax before credits · case 01
Filers with large nonrefundable credits pay local surtax on tax they never owed.
The local surtax is computed on state tax before credits · case 02
Filers with large nonrefundable credits pay local surtax on tax they never owed.
The local surtax is computed on state tax before credits · case 03
Filers with large nonrefundable credits pay local surtax on tax they never owed.
The local surtax is computed on state tax before credits · case 04
Filers with large nonrefundable credits pay local surtax on tax they never owed.
The local surtax is computed on state tax before credits · case 05
Filers with large nonrefundable credits pay local surtax on tax they never owed.
Excess nonrefundable credits make the surtax negative · case 01
Credits larger than the state tax produce a negative local surtax and an extra refund.
Excess nonrefundable credits make the surtax negative · case 02
Credits larger than the state tax produce a negative local surtax and an extra refund.
Excess nonrefundable credits make the surtax negative · case 03
Credits larger than the state tax produce a negative local surtax and an extra refund.
Excess nonrefundable credits make the surtax negative · case 04
Credits larger than the state tax produce a negative local surtax and an extra refund.
Excess nonrefundable credits make the surtax negative · case 05
Credits larger than the state tax produce a negative local surtax and an extra refund.
The local surtax is truncated to cents · case 01
Half-cent surtax amounts are dropped.
The local surtax is truncated to cents · case 02
Half-cent surtax amounts are dropped.
The local surtax is truncated to cents · case 03
Half-cent surtax amounts are dropped.
The local surtax is truncated to cents · case 04
Half-cent surtax amounts are dropped.
The local surtax is truncated to cents · case 05
Half-cent surtax amounts are dropped.
INSPECTABLE BY DESIGN
Every result has a runnable source.
Runnable implementations with recorded outputs, source hashes, and explicit contracts. Related variants share a failure mechanism and belong together in evaluation splits.
Read the methodology ↗