An audit trail lets someone who wasn’t part of the process rebuild what happened, who did it, and why the number is right. Every other benefit, from the audit opinion to the close calendar, follows from it. For decades, the trail was a human record: preparers, reviewers, approvers, and the support they attached. Now, as AI extracts contract terms, matches invoices to ledgers, and drafts conclusions, the landscape and considerations are changing. The new audit trail has to cover AI work too, or reviewers inherit a gap. This guide covers six purposes of audit trails, what changes when AI does part of the work, and a five-question test for any trail. For the full definition and a list of components, see our audit trail guide. Six Purposes of Audit Trails for Accounting and Audit Teams 1. Support the audit opinion During an audit, a company keeps records of how transactions and controls worked. The auditor, on the other hand, keeps workpapers that document how the audit tested them. In other words, auditors test the company’s trail. They don’t build it. PCAOB AS 1215 sets the bar for the auditor’s side. Audit documentation must give an experienced auditor with no prior connection to the engagement enough detail to understand the procedures performed, the evidence obtained, and the conclusions reached. It must also show who did the work, who reviewed it, and when. For significant contracts, the standard calls for abstracts or copies in the workpapers. It also requires the file to include information that cuts against the final conclusion, along with the procedures performed in response. A summary that keeps only the supporting evidence doesn’t meet that bar. 2. Prove internal control over financial reporting Section 404 of the Sarbanes-Oxley Act (SOX) splits the work in two. Management assesses how well internal control over financial reporting works, and an auditor attests to that assessment where required. SEC guidance makes management responsible for keeping the evidence, including documentation, behind its assessment. Testing a control means showing it ran: who approved, when, and what they reviewed. Without retrievable evidence, management can’t support the conclusion that the control worked. AS 1215 adds a matching rule on the audit side: when an auditor tests how a control operated, the workpapers identify the items inspected, so someone else can find the same items again. 3. Detect and deter fraud and error PCAOB’s guidance on journal entry testing draws on AS 2401, which lists traits of inappropriate entries. Two of them are entries recorded at period end or after close with little or no explanation, and entries made by people who don’t usually post them. A trail makes those patterns visible. Reviewers can spot backdated entries, edits after close, approvals out of sequence, and reversals with no stated reason. Errors leave patterns too, such as a figure edited after review or a schedule that no longer agrees to the ledger. A trail shows when the change happened and who made it, which turns a vague discrepancy into a question with an answer. Visibility deters misuse, but a trail doesn’t prevent fraud on its own. Someone still has to review it. 4. Make review and close faster With a complete trail, a reviewer can trace a balance to its source without chasing preparers for support. That means fewer follow-up requests during close and fewer rounds between management and auditors during fieldwork. New team members benefit too. They can follow a conclusion from the memo to the support without a walkthrough from the person who wrote it. 5. Satisfy regulators, tax authorities, and counterparties SOX Section 802 directed the SEC to set retention rules for auditors. SEC Rule 2-06 requires accountants to keep workpapers, plus related records that contain conclusions, opinions, analyses, or financial data, for seven years. AS 1215 also sets a seven-year period, counted from the report release date. It bars deleting documentation after the completion date. Teams can add to it, but each addition needs a date, a name, and a reason. Tax authorities want support too. The IRS requires records that back up income, deductions, and credits for as long as they may matter to administering the tax code. That generally means until the limitations period for the return expires. Counterparties such as lenders and acquirers ask for similar support in due diligence. AS 1215 even lists representatives of a party to an acquisition among those who might review audit documentation. UK note: ISA (UK) 230 applies the same experienced-auditor test. The Companies Act 2006 requires companies to preserve accounting records for three years (private companies) or six years (public companies). HMRC generally expects companies to keep records for six years from the end of the accounting period. 6. Preserve institutional knowledge A trail explains why the team reached a conclusion last year, even after the preparer has left. AS 1215 anticipates this. It names auditors who are new to an engagement and review prior-year documentation among its reviewers, along with successor auditors. Prior-period positions and memos also become precedent, so similar facts get similar treatment next year. How the Picture Changes in the Age of AI AI now does work that used to leave a human trail: reading contracts, matching documents, interpreting a standard, and drafting a memo. If that work leaves no record, the reviewer faces a black box. A traditional trail answers who did what, and when. An AI-era trail also answers what the AI read, what guidance it applied, what it concluded, and who accepted it. Three things belong in it: Inputs: the source documents and versions the AI used. If a contract has three amendments, the trail shows which one the AI read. Reasoning: the standard, policy, or firm methodology cited, with the rationale. A conclusion that cites ASC 842 and the firm’s policy gives a reviewer something to check. A conclusion with no citation asks the reviewer to take it on faith. Human accountability: the reviewer, any edits or overrides, and the sign-off. AI can draft, and people sign. The trail should show where a person agreed, changed, or rejected what the AI produced. The documentation bar stays where it is. AS 1215 defines what the file must show, whether it lives on paper, in electronic files, or in other media. PCAOB amendments to AS 1105 and AS 2301 on technology-assisted analysis took effect for audits of fiscal years beginning on or after 15 December 2025. The Board adopted them to reduce the risk of an opinion without sufficient appropriate evidence. The engagement team also stays responsible. In a July 2024 staff report on generative AI, the PCAOB noted that firms it spoke with see the team member who uses AI software as responsible for the results and documentation of the work. Those are staff observations rather than a standard, and they reflect a simple point: the team owns the conclusion. Audit evidence needs a source a reviewer can open. A chat answer with no source can’t serve as audit evidence. A cited answer that a reviewer can click through to the source can. What a Defensible Trail Looks Like in Practice Here’s an illustrative example: a lease amendment that extends the term under ASC 842. A defensible trail records each step: AI extracts the changed term from the amendment PDF, and the trail records the source page The remeasurement calculation links to the extracted figure The conclusion cites the lease modification guidance and the firm’s policy The reviewer changes the renewal option assumption, and the system logs the change with a reason The journal entry links back to every step above Then run the trace test. Pick one number from the financial statements and follow it to its source, including any AI step along the way. If the path breaks anywhere, the trail has a gap. Each link answers a question a reviewer would otherwise bring to a preparer. Which page? Where did that figure come from? Which guidance applies? Why did the assumption change? When the trail answers all four, someone who wasn’t there can follow the work, and the contract support lines up with the AS 1215 expectation for abstracts or copies of significant agreements. Five Questions to Ask About Any Audit Trail Could a reviewer who wasn’t involved reconstruct the conclusion without asking anyone? Is every figure linked to its source document? Does the trail separate AI-generated, human-entered, and human-edited work? Does it preserve changes instead of overwriting them, with role-based access? Can workpapers export in a format auditors and governance, risk, and compliance (GRC) systems accept? Start with question one. A trail that fails needs fixing before anything else. How Trullion Builds the Trail In accounting and audit, an output without a trail doesn’t cut it. Auditable AI supports work where every conclusion must be traceable, defensible, and owned. Trullion links every journal entry, contract, and disclosure back to its source document. Knowledge Room grounds AI workflows in standards, regulations, and firm methodology, so every workflow draws on the right guidance. It also connects historical work to surface precedent and past conclusions, which supports the consistency point in purpose six. Where traceability matters, Auditable AI outputs cite their source document, standard, and reasoning path, and nothing runs without a person’s sign-off. Learn more about Trullion’s Auditable AI approach, or book a demo to talk with a team member today.