Azure Functions Core Tools lets you build, configure, run, and test Azure Functions from your local development machine before deploying to Azure. A key part of that workflow is the local.settings.json file, which stores local-only configuration such as runtime settings, storage connection strings, environment variables, and other values your functions need during development.
Using Core Tools, you can initialize a Functions project, generate the required local configuration file, add settings safely, and start the Functions host with func start. This makes it possible to test HTTP-triggered functions, queue triggers, timer triggers, and other bindings locally while keeping development settings separate from production app configuration.
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Prerequisites for running Azure Functions locally
Before you create a local.settings.json file or start a function host with Azure Functions Core Tools, make sure your machine has the runtime pieces required by your chosen language stack. Azure Functions can run locally on Windows, macOS, and Linux, but the exact dependencies vary depending on whether you are building with C#, JavaScript, TypeScript, Python, Java, or PowerShell.
Install Azure Functions Core Tools
Azure Functions Core Tools provides the func command-line interface used to create projects, generate function templates, read local.settings.json, and start the local Functions host. For current projects, install Core Tools v4, which targets Azure Functions runtime 4.x. After installation, verify it from a terminal:
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func --versionshould print a 4.x version number.func --helpshould show available commands such asinit,new,start, andsettings.
Install the language runtime for your function app
Core Tools starts the Azure Functions host, but your function code still needs the correct local runtime. Install the version supported by your target Functions runtime and programming model. For example, C# projects require the .NET SDK, Node.js projects require Node.js and npm, Python projects require Python plus a virtual environment, Java projects require a JDK and Maven or Gradle, and PowerShell projects require PowerShell 7. Using unsupported versions is a common cause of startup failures, missing worker errors, or functions not being discovered.
| Function language | Typical local requirement |
|---|---|
| C# | .NET SDK compatible with your project target framework |
| JavaScript or TypeScript | Node.js, npm, and project dependencies installed with npm install |
| Python | Supported Python version, virtual environment, and packages from requirements.txt |
| Java | JDK and Maven or Gradle |
| PowerShell | PowerShell 7 and the required Azure Functions PowerShell worker support |
Prepare local storage for triggers and bindings
Many function apps need an Azure Storage account setting named AzureWebJobsStorage. Queue triggers, blob triggers, timer triggers, Durable Functions, and several host features rely on it. For local development, you can often use the Azurite storage emulator instead of a real Azure Storage account. Install Azurite, start it locally, and set AzureWebJobsStorage to UseDevelopmentStorage=true in local.settings.json. If your trigger needs cloud-only services or shared test data, use a real development storage account and keep its connection string out of source control.
Use a suitable editor and terminal
Visual Studio Code with the Azure Functions extension is a common setup, especially for creating projects, adding functions, and debugging locally. Visual Studio is also convenient for C# function apps. You can also work entirely from a terminal as long as func, your language runtime, and package managers are available on your PATH. On macOS and Linux, confirm shell permissions and executable paths; on Windows, restart the terminal after installing SDKs so environment variables are refreshed.
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Finally, confirm that local ports are available. The Functions host uses port 7071 by default for HTTP endpoints, while Azurite commonly uses 10000, 10001, and 10002. If another process is using one of these ports, either stop that process or run the Functions host with a custom port when you reach the local execution step.
Creating or opening an Azure Functions project with Core Tools
After Azure Functions Core Tools is installed, the next step is to create a new Functions project or open an existing one in your local workspace. Core Tools provides the func command-line interface, which can scaffold the folder structure, runtime configuration, and starter function files needed to run the app locally. Work from a terminal in the parent directory where you keep development projects, then create a dedicated folder for the function app.
To initialize a new project, run func init and select the worker runtime that matches your application stack. For example, choose dotnet for C# in-process functions, dotnet-isolated for the isolated .NET worker model, node for JavaScript or TypeScript, python for Python, or powershell for PowerShell functions. Core Tools creates the project files required for that runtime, such as host.json, language-specific dependency files, and local development metadata.
- New project folder: create and enter a folder first, such as
mkdir MyFunctionAppfollowed bycd MyFunctionApp. - Initialize the app: run
func init, then follow the prompts for runtime and language. - Add a function: run
func newand choose a trigger template, such as HTTP trigger, Timer trigger, Queue trigger, or Blob trigger.
For a simple HTTP-based starting point, func new can generate a function that responds to local web requests. Core Tools prompts for the template and function name, then writes the trigger configuration and source file into the project. In many runtimes, the trigger metadata is stored either in a function.json file or inferred from attributes, decorators, or framework-specific configuration. The generated files are intended to be edited, but it is useful to run the default function once before making larger changes so you know the local toolchain is working.
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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsIf you already have an Azure Functions project, open the folder that contains host.json. That file marks the root of the function app. In Visual Studio Code, use File > Open Folder and select the function app directory, not just an individual function subfolder. From the terminal, change into the same directory before running Core Tools commands. Running func start from the wrong folder is a common source of startup errors because Core Tools cannot find the host configuration or function definitions.
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Files created by project initialization
| File or folder | Purpose |
|---|---|
host.json |
Defines host-level configuration for the local and Azure Functions runtime. |
local.settings.json |
Stores local-only app settings, connection strings, and runtime values. |
function.json or source annotations |
Describes triggers and bindings, depending on the selected language model. |
| Dependency files | Examples include package.json, requirements.txt, or .csproj. |
Before moving on to settings, confirm that the project root contains host.json and at least one function. If local.settings.json is not present yet, Core Tools or editor extensions can create it during project setup, and it can also be added manually. The next configuration step is to understand what belongs in that file, how it is structured, and how to keep local secrets out of source control.
Generating and understanding the local.settings.json file
The local.settings.json file is the local configuration file used by Azure Functions Core Tools when you run a Function App on your development machine. It stores settings that would normally come from Azure App Settings in the cloud, such as storage connection strings, feature flags, API base URLs, and other environment-specific values. The file lives at the root of your Function App project, alongside files such as host.json and your function folders.
If you created a new project with Azure Functions Core Tools, the file is usually generated automatically. For example, after running func init and creating a function with func new, you should see local.settings.json in the project directory. If it is missing, create it manually in the project root with the standard structure shown below.
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"IsEncrypted": false,
"Values": {
"AzureWebJobsStorage": "UseDevelopmentStorage=true",
"FUNCTIONS_WORKER_RUNTIME": "node"
}
}
The IsEncrypted property tells Core Tools whether the values in the file are encrypted. In most local development workflows this is set to false. The Values object contains environment variables made available to your functions at runtime. For a JavaScript or TypeScript project, FUNCTIONS_WORKER_RUNTIME is typically node; for C#, it may be dotnet or dotnet-isolated; for Python, it is python; and for Java, it is java.
Common settings in local.settings.json
- AzureWebJobsStorage: Required by many triggers and by the Functions host. For local storage emulation, use
UseDevelopmentStorage=truewith Azurite running. - FUNCTIONS_WORKER_RUNTIME: Identifies the language worker used by the Functions runtime.
- APPLICATIONINSIGHTS_CONNECTION_STRING: Optional for local runs, but useful if you want telemetry sent to Application Insights.
- Custom settings: Any values your function code reads from environment variables, such as
ApiBaseUrl,QueueName, orSqlConnectionString.
For HTTP-triggered functions, AzureWebJobsStorage may not always be used directly by your code, but the host can still require it depending on the runtime version, extensions, and bindings in the project. For queue, blob, timer, Service Bus, Event Hubs, and Durable Functions scenarios, correct connection settings are more critical because the trigger listener depends on them before your function can execute.
Values from local.settings.json are loaded as environment variables when you start the project with Core Tools. In code, you typically read them using the normal environment variable APIs for your language, such as process.env.MySetting in Node.js, Environment.GetEnvironmentVariable("MySetting") in .NET, or os.environ["MySetting"] in Python. This keeps code portable between local development and Azure, where the same names should be configured under the Function App’s Application settings.
Do not commit real secrets in local.settings.json. Most Azure Functions project templates include this file in .gitignore, and it should stay that way. If another developer needs a starting point, commit a separate example file such as local.settings.sample.json with placeholder values. Each developer can then copy it to local.settings.json and fill in their own local or development credentials.
Configuring app settings and connection strings safely
After Core Tools creates local.settings.json, use it as the local-only place for values your function app needs at runtime: storage connection strings, API keys, service bus namespaces, feature flags, and environment-specific URLs. The file is read when you run the app with func start, and values under Values are exposed to your function code as environment variables. For example, a .NET function can read them with Environment.GetEnvironmentVariable("MySetting"), while JavaScript and TypeScript functions can use process.env.MySetting.
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A typical local file includes IsEncrypted and a Values object. Keep AzureWebJobsStorage for the storage account used by the Functions host, and keep FUNCTIONS_WORKER_RUNTIME aligned with your language runtime, such as dotnet-isolated, node, python, or java. Add your own application settings as sibling entries inside Values, not as nested JSON objects. Azure Functions app settings are flat name-value pairs, so use names such as ServiceBusConnection, SqlConnectionString, or ExternalApi__BaseUrl if your framework maps double underscores to configuration sections.
Safe handling for local secrets
- Do not commit
local.settings.json. The default Functions templates usually add it to.gitignore, but verify this before adding real credentials. - Use local emulators where possible. For storage-triggered development, set
AzureWebJobsStoragetoUseDevelopmentStorage=truewhen using Azurite. - Separate local and cloud configuration. Values in
local.settings.jsonare not automatically deployed as Azure app settings unless you explicitly publish them. - Avoid production secrets locally. Use development storage accounts, test queues, sandbox APIs, and least-privilege identities.
For HTTP-only functions, you may not need a real storage account during early testing, but many triggers and bindings require AzureWebJobsStorage. Queue, Blob, and Timer triggers commonly depend on it, and missing or invalid storage settings can stop the host before your function runs. If you are using Azurite, start it before running Core Tools, then confirm the connection string is set to UseDevelopmentStorage=true. If you use a real Azure Storage account, copy the connection string from the Azure portal or Azure CLI and store it only in your local file or a local secret manager.
Connection string naming depends on the binding. For example, a Service Bus trigger might reference Connection = "ServiceBusConnection", so local.settings.json must contain a matching ServiceBusConnection entry. A SQL output binding, Event Hubs trigger, or Cosmos DB binding follows the same pattern: the binding configuration names a setting, and the value of that setting is resolved at startup. If the names do not match exactly, the host reports that it cannot find the connection setting.
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You can edit the file manually or use Core Tools to manage settings. Running func settings add MySetting MyValue adds or updates a value, while func settings list displays current local settings. If you enable encryption with func settings encrypt, the file is encrypted for the current machine and user; decrypt it with func settings decrypt before copying values elsewhere. For team projects, commit a safe template such as local.settings.sample.json with placeholder values, and let each developer create their own private local.settings.json.
Running Azure Functions locally with func start
After your Azure Functions project has a valid local.settings.json file, you can start the local Functions host with Azure Functions Core Tools. Open a terminal in the project folder, the same directory that contains host.json, and run func start. Core Tools loads the runtime, reads configuration from local.settings.json, discovers your functions, and starts listening for triggers on your development machine.
For most HTTP-triggered functions, the host starts on port 7071 by default. In the terminal output, Core Tools prints the available functions and their local URLs, such as http://localhost:7071/api/MyFunction. Keep this terminal session open while you test the function. If you stop the process with Ctrl+C, the local host shuts down and endpoints are no longer available.
Starting the Functions host
Use the basic command first, then add options only when needed:
func start: Starts the local Functions host using the settings in the current project folder.func host start: Equivalent in many Core Tools versions and commonly seen in older examples.func start --port 7072: Runs the host on a different port if7071is already in use.func start --verbose: Prints more detailed runtime logs, useful when diagnosing startup or binding issues.
The command should be run from the function app root, not from a parent solution folder or an individual function subfolder. A typical project root contains host.json, local.settings.json, and either source files such as .cs, .js, .py, or a language-specific project file. If Core Tools cannot find host.json, it usually means the command is being executed from the wrong directory.
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What happens during startup
When the host starts, it validates the runtime and attempts to load each function definition. For in-process and isolated .NET projects, this may include building or loading compiled assemblies. For JavaScript, TypeScript, Python, and PowerShell projects, the worker process for that language is started. If required dependencies are missing, the startup log will usually name the package, extension, runtime version, or setting that needs attention.
| Startup item | What to check |
|---|---|
AzureWebJobsStorage |
Required by many triggers and by the host for storage-backed operations. Use a real storage connection string or Azurite for local development. |
FUNCTIONS_WORKER_RUNTIME |
Must match the project language, such as dotnet-isolated, node, python, java, or powershell. |
| Extension bundles | Required for many bindings in non-.NET projects. Check host.json if binding extensions fail to load. |
| Local port | Default is 7071. Use --port if another process is already using it. |
For non-HTTP triggers, func start still runs the host, but the function is invoked by its configured trigger rather than by visiting a URL. A queue-triggered function waits for messages in the configured queue, a timer-triggered function runs according to its schedule, and a blob-triggered function reacts to storage changes. In these cases, confirm that your local settings point to the correct emulator or development resource before expecting the function to execute.
If you edit local.settings.json while the host is running, restart func start so the new values are loaded. Some source code changes may be picked up automatically depending on the language worker and project type, but configuration changes should be treated as restart-required. This keeps local behavior predictable and closely aligned with how configuration is loaded when the function app starts in Azure.
Testing local function endpoints and triggers
After starting the Functions host with func start, test each function in a way that matches its trigger type. The terminal output lists discovered functions, their trigger types, and, for HTTP-triggered functions, the local URL. By default, HTTP endpoints run on http://localhost:7071, and routes usually follow the pattern /api/{functionName} unless a custom route is configured in the function definition.
Testing HTTP-triggered functions
For an HTTP trigger, use a browser, curl, Postman, Insomnia, or the REST Client extension in your editor. A simple GET request might look like http://localhost:7071/api/HttpExample?name=Sam. For POST requests, send the required JSON body and set the Content-Type header to application/json. Watch the terminal where func start is running; it shows invocation logs, request details, exceptions, and output binding activity.
- Anonymous authorization: local HTTP calls usually work without a function key if the trigger uses anonymous access.
- Function-level authorization: local testing can still require a key depending on your configuration and runtime behavior. If needed, append ?code=… or use the x-functions-key header.
- Custom routes: check the route value in the function configuration or attributes instead of assuming the function name is the endpoint path.
- Port conflicts: if port 7071 is unavailable, run the host on another port and call that port instead.
Testing non-HTTP triggers
Queue, blob, timer, Event Hub, Service Bus, and Cosmos DB triggers are tested by creating the event that the function listens for. For example, to test an Azure Queue Storage trigger, add a message to the configured queue in Azurite or in a real Azure Storage account. To test a blob trigger, upload a file to the configured container. The local Functions host polls or receives from the configured source, invokes the function, and prints logs in the terminal.
| Trigger type | Local test action | Setting to verify |
|---|---|---|
| HTTP | Send a request to localhost | Route, method, authorization level |
| Queue Storage | Add a message to the queue | Queue name and storage connection setting |
| Blob Storage | Upload or modify a blob | Container path and storage connection setting |
| Timer | Wait for the schedule or start manually if supported | Cron expression and timezone expectations |
| Service Bus | Send a message to the queue or topic | Entity name and connection string setting |
When using Storage-based triggers locally, Azurite is often the safest option. Set AzureWebJobsStorage in local.settings.json to UseDevelopmentStorage=true, start Azurite, and create the required queues or containers before invoking the function. If you use a real Azure resource instead, confirm that the connection string has the necessary permissions and that test messages or files will not affect production workflows.
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Troubleshooting common Core Tools and local.settings.json issues
Most local Azure Functions problems fall into a few categories: the Functions host cannot start, the runtime cannot find required settings, a trigger cannot connect to its backing service, or the installed Core Tools version does not match the project. Start by reading the terminal output from func start. The host usually prints the missing setting name, the extension that failed to load, or the port that is already in use.
Common startup and configuration problems
- Missing AzureWebJobsStorage: Many triggers and the Functions host itself require an
AzureWebJobsStoragevalue. For local development, use a real Azure Storage connection string orUseDevelopmentStorage=truewith Azurite running. - Invalid JSON in local.settings.json: A trailing comma, unescaped quote, or misplaced brace can prevent the host from reading settings. Validate the file as JSON if the host reports parsing errors.
- Wrong FUNCTIONS_WORKER_RUNTIME: The value must match the project language, such as
dotnet-isolated,dotnet,node,python,java, orpowershell. - Core Tools version mismatch: Azure Functions v4 projects should run on Azure Functions Core Tools v4. Check with
func --versionand update if the runtime behaves unexpectedly. - Port already in use: If port 7071 is occupied, start the host on another port with
func start --port 7072, then test endpoints using the new port.
If HTTP functions do not appear in the startup output, confirm that the function folder contains the expected files for your programming model. For example, older in-process models rely on function.json, while newer code-first models generate metadata differently during build or startup. Rebuild the project, restore dependencies, and check that the function method, route attributes, or trigger declarations are valid. In Node.js and Python projects, also confirm that packages are installed in the project environment and that the entry point file is in the expected location.
Storage, trigger, and extension issues
Queue, blob, timer, Service Bus, Event Hubs, Cosmos DB, and Durable Functions triggers often fail locally because an emulator, connection string, or extension is missing. If you use UseDevelopmentStorage=true, make sure Azurite is installed and running before starting the host. If you use cloud resources, verify that the connection string in local.settings.json points to the correct account or namespace and that the resource, queue, container, topic, or database already exists when the trigger expects it.
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|---|---|
| The host reports that a setting is missing | Add the exact key under the Values object in local.settings.json. |
| Storage-related triggers fail immediately | Start Azurite or replace UseDevelopmentStorage=true with a valid Azure Storage connection string. |
| Bindings or triggers are not recognized | Install or restore the required Functions extension bundle, NuGet package, npm package, or language dependency. |
| HTTP endpoint returns 404 | Check the route printed by func start, including any custom route prefix or authorization level. |
When changing settings, stop and restart the Functions host so it reloads local.settings.json. Avoid committing this file to source control because it can contain secrets; use a committed template such as local.settings.sample.json with placeholder values instead. If the project works on one machine but not another, compare the Core Tools version, language runtime version, installed dependencies, environment variables, and whether Azurite or other local services are running.
Frequently Asked Questions
How do I create a local.settings.json file if my Azure Functions project does not have one?
Run func init to create a new Functions project, then create a function with func new; Core Tools typically adds the required local project files. If local.settings.json is still missing, you can create it manually in the project root with a Values object that includes AzureWebJobsStorage and FUNCTIONS_WORKER_RUNTIME. For local development, AzureWebJobsStorage can often be set to UseDevelopmentStorage=true if you are using Azurite.
What should I put in local.settings.json for AzureWebJobsStorage?
For local development, use UseDevelopmentStorage=true when running Azurite as your local storage emulator. If your function needs to use a real Azure Storage account, set AzureWebJobsStorage to that account’s connection string instead. Avoid committing this file to source control because it often contains secrets.
Why does func start fail with a missing FUNCTIONS_WORKER_RUNTIME error?
This usually means local.settings.json does not define the runtime your project uses. Add FUNCTIONS_WORKER_RUNTIME under Values and set it to the correct value, such as dotnet, dotnet-isolated, node, python, or java. Also make sure you are running func start from the Azure Functions project folder, not a parent directory.
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How do I test an HTTP-triggered Azure Function locally?
Start the Functions host with func start, then copy the local URL shown in the terminal. Most HTTP triggers are available at a URL like http://localhost:7071/api/FunctionName. You can test it in a browser for simple GET requests, or use tools like curl, Postman, or VS Code REST Client for POST requests and custom headers.
Can I sync app settings from Azure into local.settings.json?
Yes, you can use Azure Functions Core Tools to download settings from an existing Function App with func azure functionapp fetch-app-settings <APP_NAME>. This writes settings into your local configuration so the app can behave more like the deployed version. Review the file afterward and remove or replace any production secrets you do not want stored on your development machine.
Bottom Line
Azure Functions Core Tools gives you everything you need to create a function project, generate a local.settings.json file, configure app settings, and run your functions on your development machine before deploying to Azure. The key is to keep local values accurate, store secrets safely, and remember that local.settings.json is for local development only.
From here, initialize your project, verify your runtime and storage settings, start the host with func start, and test each trigger locally. Once everything works as expected, move required settings into your Azure Function App configuration and deploy with confidence.
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