# AGENTS.md — Build guide for Fantastical ## Project scope Use EventKit to browse calendars already available on the Mac, parse a natural-language event draft and require date/time confirmation before saving. Add day/week/agenda views and switchable calendar sets. Catalogue verdict: yes. The core loop is small enough for a capable coding agent to produce a useful local version in one sitting. For Fantastical, create a polished Apple calendar client with natural-language event entry and local sets. The hard boundary is native apple integrations, widgets, sync, proposals, and years of calendar edge cases, plus calendar integrations and reliability. 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 - Do not publish, spend money, contact customers, delete source data or run irreversible migrations without the project owner's authorization.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 - macOS, Xcode and a selected deployment target. Ask for each OS permission only when its feature is enabled; code signing and distribution are separate release tasks. - Implementation components: Swift, SwiftUI and focused AppKit integrations for a macOS utility. SQLite or Codable files for local settings and history; macOS Keychain for credentials. EventKit for calendars already configured on the Mac; a date parser produces reviewed drafts before EventKit writes. - Scope boundary: Public booking pages, remote CalDAV infrastructure and Apple-platform feature parity are outside this native client. ## Stack and architecture - Swift, SwiftUI and focused AppKit integrations for a macOS utility. - SQLite or Codable files for local settings and history; macOS Keychain for credentials. - EventKit for calendars already configured on the Mac; a date parser produces reviewed drafts before EventKit writes. - Domain model: calendar sets, EventKit event identifiers, parsed draft dates, reminders and permission states ## Security and data integrity - Request EventKit access for the enabled feature and present the target calendar before writes. Keep event details and attendees out of diagnostics, preserve provider IDs and support read-only operation when write access is denied. No clipboard or keystroke capture is part of this client. - Correctness boundary: Ambiguous dates and daylight-saving transitions require review; edits preserve the provider event identity and do not silently recreate recurring series. - Keep UI state on the main actor, cancel obsolete background tasks, and avoid blocking system callbacks. Record only the selected feature scope, with clear retention controls. - Export settings and explicitly selected history without secrets. Preserve the last working configuration and provide a reset that does not delete user source files. ## Agent implementation rules - Project rule — data model: calendar sets, EventKit event identifiers, parsed draft dates, reminders and permission states - Project rule — preserve this invariant: Ambiguous dates and daylight-saving transitions require review; edits preserve the provider event identity and do not silently recreate recurring series. - Project rule — acceptance evidence: Type a meeting during a daylight-saving gap and receive a clarification; editing one recurrence occurrence leaves the rest of the series unchanged. ## Optional agent skills and references - Optional external skill: [swiftui-expert-skill](https://github.com/AvdLee/SwiftUI-Agent-Skill/blob/main/skills/swiftui-expert-skill/SKILL.md) — Build and review native SwiftUI views, state management, navigation, accessibility and rendering performance. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. - Optional external skill: [swift-concurrency](https://github.com/AvdLee/Swift-Concurrency-Agent-Skill/blob/main/skills/swift-concurrency/SKILL.md) — Design Swift async tasks, actors, isolation, cancellation and safe data sharing, including Swift 6 migration. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. - Optional external skill: [sharp-edges](https://github.com/trailofbits/skills/blob/main/plugins/sharp-edges/skills/sharp-edges/SKILL.md) — Review security-sensitive APIs and configuration for dangerous defaults and easy-to-misuse interfaces. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. 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 the actual Fantastical-inspired workflow with owned or clearly labeled sample data: Use EventKit to browse calendars already available on the Mac, parse a natural-language event draft and require date/time confirmation before saving. Add day/week/agenda views and switchable calendar sets. - Publish a reproducible walkthrough with this observable result: Type a meeting during a daylight-saving gap and receive a clarification; editing one recurrence occurrence leaves the rest of the series unchanged. - Explain who can operate this scoped tool, its setup and ongoing costs, and these remaining product gaps: Public booking pages, remote CalDAV infrastructure and Apple-platform feature parity are outside this native client. Avoid guaranteed savings, performance scores or implied endorsement. ## Engineering roadmap 1. Phase 1 — Scope and fixtures. Implement this bounded workflow: Use EventKit to browse calendars already available on the Mac, parse a natural-language event draft and require date/time confirmation before saving. Add day/week/agenda views and switchable calendar sets. Record prerequisites, select representative user-owned fixtures and document the unsupported features: Public booking pages, remote CalDAV infrastructure and Apple-platform feature parity are outside this native client. 2. Phase 2 — Durable model. Model calendar sets, EventKit event identifiers, parsed draft dates, reminders and permission states Add migrations or a versioned document format, explicit validation, stable IDs and a visible import-error report. Preserve this rule: Ambiguous dates and daylight-saving transitions require review; edits preserve the provider event identity and do not silently recreate recurring series. 3. Phase 3 — Complete the first useful path. Implement the workflow's input, review and output interface, with clear controls and explicit empty/error states. Keep UI state on the main actor, cancel obsolete background tasks, and avoid blocking system callbacks. Record only the selected feature scope, with clear retention controls. 4. Phase 4 — Permissions and integration failure. Request EventKit access for the enabled feature and present the target calendar before writes. Keep event details and attendees out of diagnostics, preserve provider IDs and support read-only operation when write access is denied. No clipboard or keystroke capture is part of this client. Request integration credentials and permissions only for the enabled feature; show a disconnected state instead of mock results. 5. Phase 5 — Portable handoff. Export settings and explicitly selected history without secrets. Preserve the last working configuration and provide a reset that does not delete user source files. Include setup, operating limits, fixture walkthrough and shutdown/restart instructions in the README. 6. Phase 6 — Acceptance scenarios. Type a meeting during a daylight-saving gap and receive a clarification; editing one recurrence occurrence leaves the rest of the series unchanged. Repeat the workflow after restart and with a denied permission or unavailable dependency; show recoverable failure rather than a success placeholder. ## Paid-product capabilities outside this build - native Apple integrations, widgets, sync, proposals, and years of calendar edge cases - multiple calendar providers - team routing and round-robin - payments - timezone edge-case maturity ## Implementation prompt WORKING SLICE Use EventKit to browse calendars already available on the Mac, parse a natural-language event draft and require date/time confirmation before saving. Add day/week/agenda views and switchable calendar sets. Build this scoped Fantastical-inspired workflow with a documented data model and visible failure states. Architecture - Swift, SwiftUI and focused AppKit integrations for a macOS utility. - SQLite or Codable files for local settings and history; macOS Keychain for credentials. - EventKit for calendars already configured on the Mac; a date parser produces reviewed drafts before EventKit writes. Prerequisites and limits macOS, Xcode and a selected deployment target. Ask for each OS permission only when its feature is enabled; code signing and distribution are separate release tasks. Outside this release: Public booking pages, remote CalDAV infrastructure and Apple-platform feature parity are outside this native client. Data model and correctness calendar sets, EventKit event identifiers, parsed draft dates, reminders and permission states Invariant: Ambiguous dates and daylight-saving transitions require review; edits preserve the provider event identity and do not silently recreate recurring series. Keep UI state on the main actor, cancel obsolete background tasks, and avoid blocking system callbacks. Record only the selected feature scope, with clear retention controls. Security and privacy Request EventKit access for the enabled feature and present the target calendar before writes. Keep event details and attendees out of diagnostics, preserve provider IDs and support read-only operation when write access is denied. No clipboard or keystroke capture is part of this client. Recovery and export Export settings and explicitly selected history without secrets. Preserve the last working configuration and provide a reset that does not delete user source files. Implementation order 1. Phase 1 — Scope and fixtures. Implement this bounded workflow: Use EventKit to browse calendars already available on the Mac, parse a natural-language event draft and require date/time confirmation before saving. Add day/week/agenda views and switchable calendar sets. Record prerequisites, select representative user-owned fixtures and document the unsupported features: Public booking pages, remote CalDAV infrastructure and Apple-platform feature parity are outside this native client. 2. Phase 2 — Durable model. Model calendar sets, EventKit event identifiers, parsed draft dates, reminders and permission states Add migrations or a versioned document format, explicit validation, stable IDs and a visible import-error report. Preserve this rule: Ambiguous dates and daylight-saving transitions require review; edits preserve the provider event identity and do not silently recreate recurring series. 3. Phase 3 — Complete the first useful path. Implement the workflow's input, review and output interface, with clear controls and explicit empty/error states. Keep UI state on the main actor, cancel obsolete background tasks, and avoid blocking system callbacks. Record only the selected feature scope, with clear retention controls. 4. Phase 4 — Permissions and integration failure. Request EventKit access for the enabled feature and present the target calendar before writes. Keep event details and attendees out of diagnostics, preserve provider IDs and support read-only operation when write access is denied. No clipboard or keystroke capture is part of this client. Request integration credentials and permissions only for the enabled feature; show a disconnected state instead of mock results. 5. Phase 5 — Portable handoff. Export settings and explicitly selected history without secrets. Preserve the last working configuration and provide a reset that does not delete user source files. Include setup, operating limits, fixture walkthrough and shutdown/restart instructions in the README. 6. Phase 6 — Acceptance scenarios. Type a meeting during a daylight-saving gap and receive a clarification; editing one recurrence occurrence leaves the rest of the series unchanged. Repeat the workflow after restart and with a denied permission or unavailable dependency; show recoverable failure rather than a success placeholder. Acceptance Type a meeting during a daylight-saving gap and receive a clarification; editing one recurrence occurrence leaves the rest of the series unchanged. Use real source data or clearly labeled fixtures. Explain unsupported input and provider failures; do not fabricate analytics, delivery receipts, accuracy claims or security guarantees. Optional agent guidance Optional external skill: [swiftui-expert-skill](https://github.com/AvdLee/SwiftUI-Agent-Skill/blob/main/skills/swiftui-expert-skill/SKILL.md) — Build and review native SwiftUI views, state management, navigation, accessibility and rendering performance. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. Optional external skill: [swift-concurrency](https://github.com/AvdLee/Swift-Concurrency-Agent-Skill/blob/main/skills/swift-concurrency/SKILL.md) — Design Swift async tasks, actors, isolation, cancellation and safe data sharing, including Swift 6 migration. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. Optional external skill: [sharp-edges](https://github.com/trailofbits/skills/blob/main/plugins/sharp-edges/skills/sharp-edges/SKILL.md) — Review security-sensitive APIs and configuration for dangerous defaults and easy-to-misuse interfaces. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. Project rule — data model: calendar sets, EventKit event identifiers, parsed draft dates, reminders and permission states Project rule — preserve this invariant: Ambiguous dates and daylight-saving transitions require review; edits preserve the provider event identity and do not silently recreate recurring series. Project rule — acceptance evidence: Type a meeting during a daylight-saving gap and receive a clarification; editing one recurrence occurrence leaves the rest of the series unchanged. ## 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.