Runtime Context
Agents, tools, and workflows can all accept RuntimeContext as a parameter, making request-specific values available to the underlying primitives.
When to use RuntimeContext
Use RuntimeContext when a primitive’s behavior should change based on runtime conditions. For example, you might switch models or storage backends based on user attributes, or adjust instructions and tool selection based on language.
Note: RuntimeContext is primarily used for passing data into specific
requests. It’s distinct from agent memory, which handles conversation
history and state persistence across multiple calls.
Setting values
Pass runtimeContext into an agent, network, workflow, or tool call to make values available to all underlying primitives during execution. Use .set() to define values before making the call.
The .set() method takes two arguments:
- key: The name used to identify the value.
- value: The data to associate with that key.
import { RuntimeContext } from "@mastra/core/runtime-context";
export type UserTier = {
"user-tier": "enterprise" | "pro";
};
const runtimeContext = new RuntimeContext<UserTier>();
runtimeContext.set("user-tier", "enterprise");
const agent = mastra.getAgent("weatherAgent");
await agent.generate("What's the weather in London?", {
runtimeContext
})
const routingAgent = mastra.getAgent("routingAgent");
routingAgent.network("What's the weather in London?", {
runtimeContext
});
const run = await mastra.getWorkflow("weatherWorkflow").createRunAsync();
await run.start({
inputData: {
location: "London"
},
runtimeContext
});
await run.resume({
resumeData: {
city: "New York"
},
runtimeContext
});
await weatherTool.execute({
context: {
location: "London"
},
runtimeContext
});Setting values based on request headers
You can populate runtimeContext dynamically in server middleware by extracting information from the request. In this example, the temperature-unit is set based on the Cloudflare CF-IPCountry header to ensure responses match the user’s locale.
import { Mastra } from "@mastra/core/mastra";
import { RuntimeContext } from "@mastra/core/runtime-context";
import { testWeatherAgent } from "./agents/test-weather-agent";
export const mastra = new Mastra({
agents: { testWeatherAgent },
server: {
middleware: [
async (context, next) => {
const country = context.req.header("CF-IPCountry");
const runtimeContext = context.get("runtimeContext");
runtimeContext.set("temperature-unit", country === "US" ? "fahrenheit" : "celsius");
await next();
}
]
}
});See Middleware for how to use server middleware.
Accessing values with agents
You can access the runtimeContext argument from any supported configuration options in agents. These functions can be sync or async. Use the .get() method to read values from runtimeContext.
export type UserTier = {
"user-tier": "enterprise" | "pro";
};
export const weatherAgent = new Agent({
name: "weather-agent",
instructions: async ({ runtimeContext }) => {
const userTier = runtimeContext.get("user-tier") as UserTier["user-tier"];
if (userTier === "enterprise") {
// ...
}
// ...
},
model: ({ runtimeContext }) => {
// ...
},
tools: ({ runtimeContext }) => {
// ...
},
memory: ({ runtimeContext }) => {
// ...
},
});You can also use runtimeContext with other options like agents, workflows, scorers, inputProcessors, and outputProcessors.
See Agent for a full list of configuration options.
Accessing values from workflow steps
You can access the runtimeContext argument from a workflow step’s execute function. This function can be sync or async. Use the .get() method to read values from runtimeContext.
export type UserTier = {
"user-tier": "enterprise" | "pro";
};
const stepOne = createStep({
id: "step-one",
execute: async ({ runtimeContext }) => {
const userTier = runtimeContext.get("user-tier") as UserTier["user-tier"];
if (userTier === "enterprise") {
// ...
}
// ...
}
});See createStep() for a full list of configuration options.
Accessing values with tools
You can access the runtimeContext argument from a tool’s execute function. This function is async. Use the .get() method to read values from runtimeContext.
export type UserTier = {
"user-tier": "enterprise" | "pro";
};
export const weatherTool = createTool({
id: "weather-tool",
execute: async ({ runtimeContext }) => {
const userTier = runtimeContext.get("user-tier") as UserTier["user-tier"];
if (userTier === "enterprise") {
// ...
}
// ...
}
});See createTool() for a full list of configuration options.