agent failed to detect that the bank feed switched from CSV to JSON mid-month and silently imported zero transactions

TL;DR

Zero transactions imported is never a quiet success: a live bank account moves every day, so a silent empty import means the pipeline broke, and here it broke because the bank changed the file format from CSV to JSON and the CSV parser read the JSON as zero valid rows without complaining. First backfill: obtain the missing days' transactions from the bank portal or API in a supported format and import them, then reconcile the account across the gap so no duplicates sneak in at the seams. Then harden the pipeline: sniff the file format from content rather than trusting the extension or the historical format, fail loudly when a parser yields zero rows from a non-empty file, and alert on any day with no import for an active account. A parser that cannot read a file must say so; silence is the actual bug.

agent failed to detect that the bank feed switched from CSV to JSON mid-month and silently imported zero transactions

Use this when

• An agent's bank feed import reports success while importing zero transactions for days or weeks.
• The bank migrated platforms or changed its statement or feed format mid-period.
• The account is active, so genuine zero-activity days are implausible.

Not for this skill when

• The account was closed or dormant and truly has no transactions. Confirm dormancy with the bank before redesigning alerts.
• The feed credentials expired and the job failed visibly. That is an auth incident with its own fix.

Steps

1. Establish the gap precisely: last successful import date, first zero import date, and the bank's own transaction list for the gap from the portal or API. Verify: the missing window and its true transactions are enumerated
2. Backfill the gap from an authoritative bank source, importing in date order and deduplicating against the days on either side. Verify: the account's transaction history is continuous across the gap with no seam duplicates
3. Reconcile the account across the whole affected month to prove the backfill restored completeness. Verify: the month reconciles with no unexplained difference
4. Inspect the files the bank now sends and identify the format change: content type, structure and first bytes, versus the parser's expectation. Verify: the format switch is characterised from the actual files
5. Implement content-based format detection, a zero-rows-from-nonempty-file hard error, and a daily no-import alert for active accounts, then test with both formats. Verify: a JSON file now parses or alarms, and a zero import can no longer pass silently

Variant phrasings

bank feed switched CSV to JSON agent imported zero transactions silently

The silent format switch symptom.

feed parser zero rows nonempty file alert format detection fix

The pipeline-hardening phrasing.

bank statement backfill gap format change reconciliation seam duplicates

The backfill procedure search.

Compatibility: Agent and ETL bank feed pipelines consuming CSV, JSON, BAI2, MT940 and CAMT files via SFTP, email or bank APIs, into ERP and reconciliation tools.

Why it happens

Parsers are usually written against the format as it existed at build time and fail in the worst possible way when formats change: not with an exception, but with an empty result set, because a JSON document contains no CSV rows to reject. Job monitoring that only checks exit codes sees a clean run. The bank, meanwhile, changed its format for its own platform reasons and considered the new format self-evident. Only content-aware validation - this file is non-empty, therefore zero transactions is impossible - converts the silent drift into an immediate, actionable alarm.

Edge cases / pitfalls

• Banks often run old and new formats in parallel briefly; detection should handle both during transitions, not swap blindly.
• Extensions lie: a .csv file may contain JSON and vice versa after a bank migration, so sniff content, not names.
• Backfill seams are duplicate-prone; dedupe on bank transaction identifiers, not on amount and date alone.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_oAsfp33hXbjZ-DUqjDbgJg