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TemplatesAgent Patterns
PrepareStep: Trim Message History
PrepareStep: Trim Message History
Demonstrate ToolLoopAgent prepareStep for trimming long message history. Pre-seeded 24-message conversation shows context compression on the first run with per-step trim telemetry.
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Problems solved
Technical challenges this implementation handles out of the box.
- Trim long message histories before each agent step
- Keep recent tool results while dropping stale turns
- Observe prepareStep compression with per-step telemetry
- Prevent unbounded context growth in ToolLoopAgent loops
Use cases
Products and workflows this pattern is designed to support.
- Long-running agents with many tool calls
- Context-window budget management
- Debugging what the model sees each step
- Production agents that must cap history size
Setup
Requirements, wiring steps, and what this pattern adds to your project.
Getting started
Pick how you want to pull this pattern in. Then wire env vars and routes the same way.
- 1
Download → Next.js app
Use Download → Next.js app in the preview toolbar. You get a zip scaffold (Pro downloads rewrite preview `/view/.../api/*` paths to `/api/*` automatically).
- 2
Extract the zip and install dependencies
Unzip the archive, then run `pnpm install` (or npm / yarn) in the project folder.
- 3
Fill .env.local
The download includes .env.local placeholders when needed. Add real values for: OPENAI_API_KEY.
- 4
Customize the agent and tool files
Adapt prompts, tools, and stop conditions in the generated project for your product.
- 5
Run the app and open the pattern route
Run `pnpm dev`, open the setup/checklist page if present, then navigate to the generated pattern route and verify responses.
Environment variables
OPENAI_API_KEYGet key
Capabilities
AI SDK APIs
ToolLoopAgentprepareStepstepCountIstoolgatewayProviders
OpenAI
Files added
11 filesapp/page.tsxapp/layout.tsxapp/api/trim/route.tscomponents/trim-demo.tsxcomponents/trim-timeline.tsxcomponents/seed-preview.tsxlib/trim-config.tslib/seed-conversation.tslib/trim-agent.tstools/append-note.tsREADME.md
Dependencies
15 totalnpm packages
5AISDKlucide-reactNext.jsReactZod
Registry components
alertbadgebuttoncardcollapsiblelabelscroll-areaskeletonswitchtooltip
Critical files
lib/trim-agent.tsToolLoopAgent with prepareStep that returns messages.slice(-KEEP_RECENT) when over MAX_MESSAGES. Logs trim events per step in a collector array.
lib/seed-conversation.tsStatic 24-message ModelMessage[] fixture so the demo shows trimming immediately without user-built history.
trim/route.tsRuns agent.generate({ messages: [...seeded, finalUser] }) and returns trimEvents, hero metrics, and optional compare run without trim.
tools/append-note.tsSingle demo tool for the agent to call once before summarizing.
Requirements
- Complexity
- Intermediate
- Setup time
- ~10 minutes
- Node
- 24+
- Memory
- 512MB
