Deferred revenue (Details)	6 Months Ended	12 Months Ended
Jun. 30, 2026 CNY (¥)	Jun. 30, 2026 USD ($)	Dec. 31, 2025 CNY (¥)
Deferred revenue
Balance at the beginning of the year	¥ 40,942	$ 6,034	¥ 620,000
Decrease in contract liabilities from recognizing revenue during the year included in the contract liabilities at the beginning of the year	(40,942)	(6,034)	(620,000)
Increase in contract liabilities from billings in advance of performance obligation under contracts	625,320	92,161	40,942
Balance at the end of the year	¥ 625,320	$ 92,161	¥ 40,942

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-8

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-2

Name:	us-gaap_ContractWithCustomerLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant