# AGENTS.md — Build guide for Pirsch ## Project scope Collect bounded first-party pageview/event payloads for one owned site and display path, referrer and event totals with retention controls. Catalogue verdict: kinda. The core loop is buildable, but a dependable replacement becomes a real weekend or multi-day project. For Pirsch, collect cookieless page views and custom events with compact dashboards. The hard boundary is hosted reliability, privacy operations, apis, email reports, and scale, plus data pipeline reliability and analytical depth. Use the implementation prompt below to define the deliverable. Complete each phase's acceptance checks before extending the scope. ## Working agreement - Inspect the repository and its existing instructions before choosing paths, dependencies or commands. Keep one coherent stack and explain changes to the proposed architecture. - Plan a vertical slice that accepts a real input and produces the useful output described below. Persist only the state the prompt calls for; respect memory-only and upstream-managed workflows. Use fixtures only when they are clearly labelled. - After scaffolding, document the actual install, development, check and build commands in README and keep them synchronized with the package or project manifest. Do not report commands as successful unless they ran. - Work in small steps. At handoff, list implemented flows, checks actually performed, remaining blockers, and any credentials or provider setup the owner must supply. - Do not publish, spend money, contact customers, delete source data or run irreversible migrations without the project owner's authorization. ## Prerequisites - Runtime and tools: TypeScript, Node, Express, better-sqlite3, a small first-party browser tracker and a durable aggregation worker with an authenticated server-rendered dashboard. - Before starting: One owned site, HTTPS tracker/intake URLs, private dashboard credentials, a declared event schema, a retention/deletion policy, and synthetic SPA navigation, duplicate, invalid-site and sensitive-URL fixtures. ## Stack and architecture - TypeScript, Node, Express, better-sqlite3, a small first-party browser tracker and a durable aggregation worker with an authenticated server-rendered dashboard - Data design: Store Site, Event, DailyAggregate and RetentionPolicy; strip query strings or allowlist campaign parameters and reject arbitrary event-property blobs. - Setup: One owned site, HTTPS tracker/intake URLs, private dashboard credentials, a declared event schema, a retention/deletion policy, and synthetic SPA navigation, duplicate, invalid-site and sensitive-URL fixtures ## Security and data integrity - Treat the browser site ID as public, not a secret credential. Validate registered sites, allowed browser origins and bounded event schemas, with per-site quotas; an Origin header is only one abuse signal. Strip unapproved URL parameters, referrer details and event properties before logs, queues or storage. Deduplicate by site and client event ID within a documented window. Store accepted events and pending aggregation state durably; update aggregates and mark events processed in one transaction so retries cannot count twice. Define event-time/timezone and late-event rules, retention and deletion across raw data and aggregates. Keep dashboard queries scoped to the authenticated site owner and do not infer audited people from event counts. - Cookieless does not automatically mean anonymous or legally compliant. Define aggregation and any visitor estimates explicitly; exclude raw IP retention unless separately justified and disclosed. - Keep secrets outside client bundles and exported projects; document what leaves the device and make retention/deletion controls visible. ## Agent implementation rules - Project rule — domain: Store Site, Event, DailyAggregate and RetentionPolicy; strip query strings or allowlist campaign parameters and reject arbitrary event-property blobs. - Project rule — scope and recovery: Cookieless does not automatically mean anonymous or legally compliant. Define aggregation and any visitor estimates explicitly; exclude raw IP retention unless separately justified and disclosed. - Project rule — acceptance: Send duplicate navigation events and a URL containing an email; apply the stated deduplication policy and discard private parameters before persistence. - Project rule — delivery: document real setup commands and permissions; do not claim a build, accuracy level, performance result or security certification that has not been demonstrated. ## Optional agent skills and references - Recommended skill: [web-design-guidelines](https://github.com/vercel-labs/agent-skills/blob/main/skills/web-design-guidelines/SKILL.md) — review keyboard access, focus, validation, error recovery and the readable work/review interface or HTML report. Follow the maintainer's installation instructions and match its requirements to the chosen runtime. - Recommended skill: [sharp-edges](https://github.com/trailofbits/skills/blob/main/plugins/sharp-edges/skills/sharp-edges/SKILL.md) — review configuration and API defaults against the app-specific invariants and recovery boundaries above; this is not a security certification. Follow the maintainer's installation instructions and match its requirements to the chosen runtime. Read the linked SKILL.md and its dependencies before adding a skill. Select only the skills matching this project's runtime and task; their documentation does not supply API access, credentials or approval to perform external actions. Pin the reviewed revision where the tool supports it. Follow the chosen agent's documented project-level installation mechanism. ## Distribution ideas These are optional planning notes. Obtain the owner's approval before publishing or contacting anyone. - Demonstrate this working slice using synthetic or explicitly authorized non-sensitive examples: Collect bounded first-party pageview/event payloads for one owned site and display path, referrer and event totals with retention controls. - Share a synthetic example export and the acceptance walkthrough; keep real customer, health, financial and source data private: Send duplicate navigation events and a URL containing an email; apply the stated deduplication policy and discard private parameters before persistence. - State the limits before asking someone to replace their existing tool: Cookieless does not automatically mean anonymous or legally compliant. Define aggregation and any visitor estimates explicitly; exclude raw IP retention unless separately justified and disclosed. ## Engineering roadmap 1. Phase 1 — Pin the working slice and create its example input: Collect bounded first-party pageview/event payloads for one owned site and display path, referrer and event totals with retention controls. Confirm setup: One owned site, HTTPS tracker/intake URLs, private dashboard credentials, a declared event schema, a retention/deletion policy, and synthetic SPA navigation, duplicate, invalid-site and sensitive-URL fixtures. 2. Phase 2 — Implement persistence and write-time invariants before decorating the UI: Store Site, Event, DailyAggregate and RetentionPolicy; strip query strings or allowlist campaign parameters and reject arbitrary event-property blobs. 3. Phase 3 — Connect the working view to real saved state. Treat the browser site ID as public, not a secret credential. Validate registered sites, allowed browser origins and bounded event schemas, with per-site quotas; an Origin header is only one abuse signal. Strip unapproved URL parameters, referrer details and event properties before logs, queues or storage. Deduplicate by site and client event ID within a documented window. Store accepted events and pending aggregation state durably; update aggregates and mark events processed in one transaction so retries cannot count twice. Define event-time/timezone and late-event rules, retention and deletion across raw data and aggregates. Keep dashboard queries scoped to the authenticated site owner and do not infer audited people from event counts. 4. Phase 4 — Expose the app-specific limits and recovery path in context: Cookieless does not automatically mean anonymous or legally compliant. Define aggregation and any visitor estimates explicitly; exclude raw IP retention unless separately justified and disclosed. 5. Phase 5 — Walk through this concrete acceptance case and preserve its exported evidence: Send duplicate navigation events and a URL containing an email; apply the stated deduplication policy and discard private parameters before persistence. Finish the README and backup/restore instructions; report unfinished capabilities explicitly. ## Paid-product capabilities outside this build - hosted reliability, privacy operations, APIs, email reports, and scale - identity stitching - session replay - warehouse connectors - high-volume global ingestion and support ## Implementation prompt Build the following focused alternative to Pirsch. This is a deliberately limited personal or small-team substitute, not parity with the paid service. WORKING SLICE Collect bounded first-party pageview/event payloads for one owned site and display path, referrer and event totals with retention controls. SETUP AND ARCHITECTURE Use TypeScript, Node, Express, better-sqlite3, a small first-party browser tracker and a durable aggregation worker with an authenticated server-rendered dashboard. Prerequisites: One owned site, HTTPS tracker/intake URLs, private dashboard credentials, a declared event schema, a retention/deletion policy, and synthetic SPA navigation, duplicate, invalid-site and sensitive-URL fixtures. Before integrating anything, record actual versions and permissions, plus model files or provider limits only where used, in the README; make unavailable dependencies visible rather than simulating success. DOMAIN MODEL AND INVARIANTS Store Site, Event, DailyAggregate and RetentionPolicy; strip query strings or allowlist campaign parameters and reject arbitrary event-property blobs. IMPLEMENTATION CONTRACT Treat the browser site ID as public, not a secret credential. Validate registered sites, allowed browser origins and bounded event schemas, with per-site quotas; an Origin header is only one abuse signal. Strip unapproved URL parameters, referrer details and event properties before logs, queues or storage. Deduplicate by site and client event ID within a documented window. Store accepted events and pending aggregation state durably; update aggregates and mark events processed in one transaction so retries cannot count twice. Define event-time/timezone and late-event rules, retention and deletion across raw data and aggregates. Keep dashboard queries scoped to the authenticated site owner and do not infer audited people from event counts. Provide an input/setup view, the main work view, and a review/export view appropriate to this workflow. Preserve the last saved state if a job or save fails. Include empty, loading, permission-denied, partial and retryable-error states. Log identifiers and error categories without secret values or unnecessary private content. APP-SPECIFIC BOUNDARY AND RECOVERY Cookieless does not automatically mean anonymous or legally compliant. Define aggregation and any visitor estimates explicitly; exclude raw IP retention unless separately justified and disclosed. ACCEPTANCE SCENARIO Send duplicate navigation events and a URL containing an email; apply the stated deduplication policy and discard private parameters before persistence. Also reopen the app after an interrupted operation, confirm the saved record/export remains inspectable, and document the recovery action. These are implementation acceptance requirements, not a claim that this guide has been tested. DELIVERY Deliver a runnable repository with migrations or project-format versioning, a non-sensitive example, environment/permission setup, the exact manual acceptance steps, and a backup/export-and-restore walkthrough. Implement the working slice before optional integrations; list any deferred paid-product capabilities honestly. Do not add capabilities outside the working slice just to resemble the original product. PROJECT RULES FOR AGENTS.md Keep the domain invariants above executable at the write boundary. Propose scope changes before adding providers or permissions. Never fabricate source evidence, publish results, identity matches or successful delivery. Preserve user originals and require an explicit confirmation for destructive changes or external publication. ## Completion evidence Demonstrate the prompt's acceptance scenarios against the scoped workflow. Include setup from a clean checkout and failure recovery. Check persistence across restart and export/restore only for the state the prompt says to store; for memory-only tools, confirm that temporary content is discarded as specified. Record actual results and remaining limitations. A detailed plan alone does not establish a working replacement.