MetaTrader Files & Configuration Glossary — .set, .tpl, Magic Number

MetaTrader's file ecosystem is one of the things experienced EA users learn by exposure and rarely have explained clearly. This cluster collects the file formats and configuration concepts you need to understand to operate EAs at scale — running multiple EAs on one account, switching between configurations cleanly, sharing setups with other traders, and avoiding the operational pitfalls of multi-EA accounts.

The `.set` file (MetaTrader preset) stores EA input parameter values. Vendors distribute recommended `.set` files alongside their EAs (e.g. `MyEA_EURUSD.set`, `MyEA_XAUUSD.set`), and traders create their own after parameter optimisation. Managing `.set` files well — naming conventions, version control, documentation — is part of operating EAs as a professional rather than a hobbyist.

The `.tpl` file (chart template) stores complete chart visual configuration including applied indicators, drawing objects, colour scheme, and the attached EA. Templates let you recreate complex chart setups across charts. Vendor-distributed `.tpl` files typically include their recommended indicator overlays alongside the EA itself.

Magic numbers are the unique identifiers that distinguish one EA's trades from another's on the same account. Running multiple EAs on a single account requires careful magic-number assignment — conflicts produce subtle bugs where EAs modify or close each other's positions. Standard practice is to use 4-8 digit unique integers per EA instance, documented in a central registry for the account.

Symbol mapping addresses the broker-naming-convention problem: the same instrument (EUR/USD) is named differently across brokers (`EURUSD`, `EURUSD.r`, `EURUSDpro`, etc.). EAs that hardcode symbol names break when switched between brokers; robust EAs include mapping logic or expose symbol names as configurable inputs.

For commercial EAs: vendor distribution typically includes both `.ex5`/`.ex4` binary files and `.set` files for recommended configurations. Higher-quality vendors also include `.tpl` files for recommended chart setups and detailed documentation of magic-number defaults, symbol-mapping configuration, and parameter explanations.

For self-developed EAs: invest time in the operational layer (clean parameter exposure, magic-number management, documentation) even though it feels less glamorous than strategy development. Production operation depends on operational quality more than strategy sophistication; a well-operated mediocre strategy beats a poorly-operated brilliant one.