GitHub Copilot: Commands, Context and How to Use Them Together

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A reference note on the three command types in GitHub Copilot Chat and how to combine them effectively for Java development.

Three types of input control how Copilot understands your request:

• / slash commands — tell Copilot what to do
• @ agents — tell Copilot where to look
• # context variables — tell Copilot what to focus on

A strong prompt combines all three. Example: @workspace /explain #file:PaymentService.java — how does this interact with the repo?

Used inside Copilot Chat sidebar or inline chat (Ctrl+I). These are pre-optimized prompt macros — not the same as typing the words manually.

/explain — breaks down what code does, its logic and flow

Use when: reading unfamiliar code, onboarding, reviewing a PR
Example: /explain #file:ReconciliationService.java

/fix — diagnoses and corrects a specific bug or error

Use when: you have a concrete error, not a vague "something is wrong"
Example: /fix #selection — @Transactional not rolling back on RuntimeException

/tests — generates JUnit/Mockito test cases for a class or method

Use when: after writing a service method, before raising a PR
Example: /tests #file:PaymentService.java — cover nulls and exception paths

/refactor — restructures code without changing behavior

Use when: method is too long, code is repetitive, SRP is being violated
Example: /refactor #selection — extract helper methods, keep behavior same

/doc — writes Javadoc for selected class or method

Use when: documenting public API methods before committing
Example: /doc #editor — add @param, @return, @throws to all public methods

/new — scaffolds a new Spring Boot component from a description

Use when: starting a new feature from scratch inside an existing project
Example: /new Spring Boot REST controller for /api/accounts

These tell Copilot which environment or surface to pull context from.

@workspace — scans the entire open project before answering

Use when: asking cross-cutting questions across multiple files
Example: @workspace where is datasource configuration defined?

@terminal — reads your terminal, understands CLI output and errors

Use when: build failed, Maven error, test runner output is cryptic
Example: @terminal /fix #terminalLastCommand

@vscode — answers questions about the IDE itself, not your code

Use when: setting up debugger, launch config, keybindings, extensions
Example: @vscode how do I set up launch.json for a Spring Boot app?

@github — pulls in PR details, issues, commit history from GitHub

Use when: reviewing PRs, understanding what a commit changed
Example: @github summarize PR #142

These pin specific content into the context window of your prompt.

#file:FileName.java — attaches a specific file regardless of which tab is active

Use when: you want to focus on one file precisely
Example: /explain #file:AccountService.java

#editor — attaches whichever file your cursor is currently active in

Use when: you are already inside the file you want to ask about
Note: if you have multiple tabs open, #editor is only the active tab

#selection — attaches the code you have highlighted in the editor

Use when: asking about one method or block, not the whole file
Example: /fix #selection — null check missing before this call

#terminalLastCommand — passes the last terminal command and its output

Use when: build or test just failed and you want instant diagnosis
Example: @terminal /fix #terminalLastCommand

#codebase — semantic search across all indexed project files

Use when: you don't know which file contains what you're looking for
Example: which class handles Kafka error retry? #codebase

You can stack multiple #file: references in one prompt: /explain #file:AccountService.java #file:PaymentController.java — how do these interact?

#editor is just a lazy shorthand for the active tab. Useful when deep in one file. #file: is more explicit and reliable when jumping between multiple open tabs.

Understand an unfamiliar service:

@workspace /explain #file:ReconciliationService.java — dependencies and responsibilities

Fix a Maven build failure:

@terminal /fix #terminalLastCommand

Write tests after implementing a method:

/tests #file:PaymentService.java — cover edge cases, nulls, exception paths using Mockito

Refactor a long method:

/refactor #selection — extract helpers, apply SRP, keep behavior unchanged

Document before committing:

/doc #editor — Javadoc on all public methods with @param @return @throws

Debug a Spring transaction issue:

/fix #selection — @Transactional not rolling back, REQUIRES_NEW propagation

Trace where a config is wired:

@workspace where is datasource configured? check application.yml and @Configuration classes #codebase

Understand a pom.xml dependency:

@workspace /explain #file:pom.xml — what does the resilience4j dependency do here?

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