> ## Documentation Index
> Fetch the complete documentation index at: https://docs.agentium.in/llms.txt
> Use this file to discover all available pages before exploring further.

# Dependencies & Runtime Injection

> Inject runtime variables into agent instructions and messages

## Overview

Dependencies let you inject runtime variables into your agent's instructions and user messages using `{template}` syntax. Values can be static, synchronous functions, or async functions — all resolved at the start of each run.

## Quick Start

```typescript theme={null}
import { Agent, openai } from "@agentium/core";

const agent = new Agent({
  name: "support-agent",
  model: openai("gpt-4o"),
  instructions: "You are a support agent for {company}. Today is {date}. The user's plan is {plan}.",
  dependencies: {
    company: "Acme Corp",
    date: () => new Date().toLocaleDateString(),
    plan: async () => {
      // fetch from database
      return "Enterprise";
    },
  },
});

const output = await agent.run("What features do I have access to?");
```

## Per-Run Overrides

```typescript theme={null}
const output = await agent.run("Help me with billing", {
  dependencies: {
    plan: "Pro",       // override the default
    locale: "en-US",   // add a new dependency
  },
});
```

## Accessing in Tools

Resolved dependencies are available in `RunContext`:

```typescript theme={null}
import { defineTool } from "@agentium/core";

const lookupTool = defineTool({
  name: "lookup_account",
  description: "Look up the user's account",
  parameters: z.object({}),
  execute: async (args, ctx) => {
    const company = ctx.dependencies.company;
    const plan = ctx.dependencies.plan;
    return `Account: ${company}, Plan: ${plan}`;
  },
});
```

## Template Syntax

* `{key}` — replaced with the resolved value
* Unknown keys are left as-is (e.g. `{unknown}` stays `{unknown}`)
* Templates work in both `instructions` and string `input`

## Resolution Order

1. Agent-level `dependencies` from config
2. Per-run `dependencies` from `RunOpts` (overrides agent-level)
3. All callable values are invoked and awaited
4. Results are flattened to `Record<string, string>`