Developer Builds Ad-Free MCP Prayer Times Plugin: Precise Calculations with 12 Algorithms

When AI Assistants Meet Daily Prayer: An Overlooked Developer Pain Point

For many developers, most of the workday is spent inside ChatGPT—writing code, sketching architecture diagrams, debugging automation workflows. But one daily necessity remains stubbornly difficult to handle within AI conversations: checking daily prayer times.

A developer recently shared his frustration: most mobile prayer apps are riddled with intrusive ads, location tracking, or opaque default calculation parameters, with results that can differ from local mosque schedules by up to 15 minutes. And when asking a large language model directly, the model often guesses the user's location based on the cloud server's IP address, making the results completely unusable.

This pain point gave rise to an open-source solution—Muslim Prayer Reminder, an ad-free ChatGPT plugin and MCP tool.

12 Astronomical Calculation Standards, No "Black Box" Defaults

The core design decision behind this plugin is to make all calculation logic transparent. It ships with 12 authoritative astronomical calculation standards, covering the algorithmic systems of major Islamic scholarly institutions worldwide:

• Umm Al-Qura (adopted in Mecca)
• Muslim World League (MWL)
• Egyptian General Authority of Survey
• ISNA (Islamic Society of North America)
• And several other regional standards

Unlike most apps on the market, this plugin explicitly states in every response which calculation standard and reasoning basis were used, rather than hiding behind an invisible default option. Users know exactly what parameters their results are based on.

Meanwhile, for Asr (afternoon prayer) time calculation, the plugin offers an explicit toggle between the standard shadow ratio (Shafi'i, Maliki, Hanbali schools) and the Hanafi school's juristic method. This detail is crucial for users who follow different schools of jurisprudence—the difference in Asr time calculation can directly affect whether the prayer is completed within the correct time window.

How are prayer times actually calculated? Traditionally, the times of the five daily prayers are determined by the sun's position in the sky: Fajr begins when the first light appears on the dawn horizon, Maghrib begins at sunset, Isha begins when twilight fades, and Asr is determined by when an object's shadow reaches a specific multiple of its length. Different institutions define different solar depression angles for "dawn light" and "twilight fading"—for example, the Muslim World League uses 18°/17°, ISNA uses 15°/15°, and Umm Al-Qura uses 18.5° combined with a fixed 90-minute Isha delay. It is precisely these differences in angle values that cause results to vary by more than ten minutes at the same location under different standards. By openly listing these 12 parameter sets and allowing users to explicitly choose, the plugin essentially returns the traditionally buried "calculation options" back to the user.

Mathematical Handling at High Latitudes and Transparency

For Muslims living in high-latitude regions such as Northern Europe and northern Canada, prayer time calculation has always been a thorny problem—during summer, twilight may never fully dissipate throughout the night, and traditional solar angle calculations become invalid.

This plugin adopts explicit mathematical approximations for such cases and proactively discloses which approximation method was used in its response. This approach of "clearly stating what I did" is more trustworthy in the field of religious time calculation—where accuracy is extremely sensitive—than a seemingly precise result with unknown origins.

The essence of the high-latitude problem is geometric: when the summer sun never drops to a sufficiently low angle, the judgment angles for Fajr and Isha are never reached, and the algorithm has no mathematical solution. Common approximation methods include: the "middle of the night" method (dividing the period between sunset and sunrise by a fixed ratio), the "one-seventh" method (splitting the night into seven parts), the "angle-based" method (substituting a fixed angle like 48° for the actual angle), and the "Mecca time" method (directly adopting Mecca's prayer times). There is no "single correct answer" to these methods, and acceptance varies widely among different communities. Therefore, by explicitly disclosing the approximation scheme used, the plugin essentially returns the right to choose—and the right to know—to the user, rather than letting software decide on their behalf.

One-Sentence Setup, Automated Daily Reminders

The plugin is very intuitive to use. Users can configure location and calculation standard with a single prompt:

"Set my prayer time location to London, UK, using the Muslim World League standard, with the Shafi'i method for Asr. Then check today's prayer times."

Furthermore, it can be integrated with ChatGPT's scheduled task feature for automated daily reminders:

"Set up a daily scheduled task to check the prayer times for my location every morning at 7:00."

This automation capability transforms prayer time checking from an action that requires active initiation into a silently running daily service. For developers with tight work schedules, this eliminates a recurring point of attention interruption.

Zero Data Tracking Privacy Commitment

On the privacy front, this plugin's design stance is equally clear:

• No user account system
• No subscription fees
• No ads
• No external tracking or telemetry

For a tool that needs to know the user's precise geographic location to function properly, a zero-tracking commitment is not an optional bonus—it is the foundation for building trust. Considering that prayer times are deeply tied to a user's religious practice and daily life patterns, the sensitivity of such data is obvious to everyone.

The Value of Vertical Tools in the MCP Ecosystem

This plugin is released in an MCP (Model Context Protocol) compatible form, meaning it is not limited to the ChatGPT platform and can theoretically be invoked by any AI assistant that supports the MCP protocol. This represents an interesting trend in the current AI tool ecosystem: developers are transforming niche needs they encounter in daily life into standardized AI-invocable tools.

The emergence of such vertical tools is gradually evolving AI assistants from "general conversation interfaces that can chat about anything but master nothing" into practical platforms capable of reliably handling specific tasks. Prayer time lookup is just one case, but its design philosophy—transparent calculation, privacy-first, automation integration—offers useful reference for building other vertical AI tools as well.

The plugin is now available on the ChatGPT store, and the developer welcomes other developers and open-source contributors to participate in edge-case testing and provide feedback.

MCP (Model Context Protocol) is a protocol standard proposed and open-sourced by Anthropic in late 2024, designed to establish a unified connection method between AI assistants and external tools and data sources. It can be likened to a "USB-C port for the AI world": previously, every plugin had to be adapted separately for a specific platform, but tools conforming to the MCP protocol only need to be implemented once to be invoked by ChatGPT, Claude Desktop, Cursor, Continue, or any other client supporting the protocol. MCP typically runs through local or remote server processes, and AI models invoke the "tools," "resources," and "prompts" it exposes as needed during conversations. This decoupling means developers don't have to bind themselves to a closed ecosystem, and the portability and lifespan of tools are greatly extended—this is also the core motivation behind vertical small tools like Muslim Prayer Reminder choosing to release in MCP form.

One-line Summary

Developer builds an ad-free, zero-tracking ChatGPT plugin and MCP tool for precise daily prayer time lookup.

Paragraph Summary

Addressing the daily pain point of being unable to smoothly check prayer times in AI conversations, a developer created the open-source tool Muslim Prayer Reminder. Released as a ChatGPT plugin and in MCP-compatible form, it ships with 12 authoritative astronomical calculation standards (such as Umm Al-Qura, MWL, ISNA, etc.) and explicitly states the standard and reasoning basis used in every response, avoiding opaque defaults. For Asr time, the plugin provides a toggle between the Shafi'i/Maliki/Hanbali and Hanafi juristic methods; for the missing-twilight problem in high-latitude regions like Northern Europe, it uses clearly disclosed mathematical approximations. Users can configure location and standard with a single prompt and combine it with ChatGPT scheduled tasks for automated daily reminders. The plugin commits to zero data tracking: no accounts, no subscriptions, no ads, no telemetry, and can be invoked by any AI assistant supporting the MCP protocol.