What the Truth File is
A single markdown or Notion document owned by one accountable person. It contains every number the growth programme has ever claimed, every source that number came from, every methodology footnote, and every date the number was last reviewed. Anyone in the organisation can read it; only the owner can edit it. It exists so the growth team can never accidentally lie, including to itself.
Required sections
1) Business context: product, geography, category, stage. 2) Unit economics: ARPU, margin, payback, allowable CAC, allowable CPI, with date of last review. 3) KPI tree: north-star, tier-1 metrics, tier-2 diagnostics. 4) Source-of-truth map: which system owns which metric. 5) Event taxonomy: canonical event names, definitions, firing rules. 6) Access ledger: who has which permission in which platform. 7) Claim ledger: every external claim ever made, with source. 8) Change log: what changed and why.
The claim ledger
Every time the team plans to say something externally, in an ad, on the website, in a deck, in a press quote, the claim goes into the ledger first. The claim, the source, the date the source was verified, and the person who verified it. If the source is 'internal cohort analysis', the analysis file is linked. If the source is 'industry benchmark', the report is linked with page number. Claims without a ledger entry cannot ship.
The KPI tree
One north-star (e.g. D30 retained payers). Three or four tier-1 metrics that mathematically compose the north-star (installs × activation × trial-start × trial-to-paid × D30 retention). Ten or twelve tier-2 diagnostics that explain movement in tier-1. Nothing more. Dashboards that show 60 metrics on one page are decorative; the Truth File shows the tree and the maths that connects it.
Source-of-truth architecture
MMP owns install and paid-attribution truth. Product analytics (Amplitude/Mixpanel) owns session and event truth. Firebase owns crash and technical-quality truth. Finance owns revenue truth. Store consoles own impression, page-view and store-conversion truth. The map documents which system owns which number and, critically, which number to trust when they disagree.
Access and least-privilege
Every platform (ad accounts, MMP, analytics, store consoles, DNS, ESP) has an access ledger row: who has admin, who has editor, who has read-only, and when access was last audited. Least-privilege is the default; escalations are logged. When someone leaves the team, the ledger is the checklist. This is boring and unglamorous and prevents the majority of real-world security incidents in growth teams.
The weekly reconciliation
One 30-minute meeting per week. Read the tier-1 numbers from source. Reconcile MMP-vs-Firebase install variance. Reconcile paid-vs-finance revenue variance. Note any drift over the documented threshold. Update the change log. That's it. The purpose is not to make decisions, decisions happen in operating meetings. The purpose is to keep the numbers you make decisions on true.
Why boards trust it
Board scepticism comes from opacity, 'where did that number come from, and can I trust the person who made it?' The Truth File answers both questions in the same document. Every quarterly board deck cites Truth File section numbers. Every question gets a same-day answer with a source. Trust compounds. The next funding round, the next hire, the next partnership all move faster because the numbers are pre-defended.