Summarizer Agent

The worker-only example in the set — no browser UI, just a topic consumer that enriches database rows.

Source: examples/summarizer-agent/

There is no model dependency. The summarizer is deterministic so the example is easy to read and the test is stable.

What it does

A row lands in blog.blogs
KalamDB routes the change into blog.summarizer
The worker consumes the topic with runConsumer()
The worker writes summary back into the same row
Failures are stored in blog.summary_failures

Use change.data as the blog row inside onChange(). Because blog.blogs is a SHARED table, change.user is undefined in this example.

Prerequisites

Node.js 18+
Kalam CLI

Quick start

BASH

1cd examples/summarizer-agent2npm install3kalam dev

kalam dev starts the local server, applies kalam/schema.sql, keeps kalam/migrations/ current, and runs the worker with npm run start.

Schema and topic route

SQL

1CREATE NAMESPACE IF NOT EXISTS blog;2 3CREATE SHARED TABLE IF NOT EXISTS blog.blogs (4    blog_id BIGINT PRIMARY KEY DEFAULT SNOWFLAKE_ID(),5    content TEXT NOT NULL,6    summary TEXT,7    created TIMESTAMP NOT NULL DEFAULT NOW(),8    updated TIMESTAMP NOT NULL DEFAULT NOW()9);10 11CREATE SHARED TABLE IF NOT EXISTS blog.summary_failures (12    run_key TEXT PRIMARY KEY,13    blog_id TEXT NOT NULL,14    error TEXT NOT NULL,15    created TIMESTAMP NOT NULL DEFAULT NOW(),16    updated TIMESTAMP NOT NULL DEFAULT NOW()17);18 19CREATE TOPIC blog.summarizer;20ALTER TOPIC blog.summarizer ADD SOURCE blog.blogs ON INSERT WITH (payload = 'full');21ALTER TOPIC blog.summarizer ADD SOURCE blog.blogs ON UPDATE WITH (payload = 'full');

Worker pattern

typescript

1await runConsumer({2    client,3    name: 'summarizer',4    topic: 'blog.summarizer',5    groupId: 'summarizer',6    onChange: async (_ctx, change) => {7        const row = change.data;8        const summary = `Summary: ${row.content.slice(0, 80)}`;9        // UPDATE blog.blogs SET summary = ... WHERE blog_id = row.blog_id10    },11});

Files worth reading

File	Purpose
`src/agent.ts`	Full worker logic
`kalam.toml`	`kalam dev` project config
`kalam/schema.sql`	Schema, topic route, and seed row
`kalam/migrations/0001_init.sql`	Initial migration

Verify it works

BASH

1npm test

The integration test inserts a blog row and waits until the worker writes the summary field back.

Next steps

Topic Consumer (Rust) — same pattern in Rust
Chat With AI — topic worker plus browser UI
TypeScript agents guide