---
title: "Sidecar (parasitic tap) · agent topology · Agent Fieldbook"
url: https://agentfieldbook.org/design/topologies/side-care/
description: "A side-agent rides beside the main agent chain, tapping events without being on the primary path. Typical memory-harvesting pattern."
section: "Design · Topologies"
source: Agent Fieldbook — generated from the published page
---

# Sidecar (parasitic tap)

A side-agent rides beside the main agent chain, tapping events without being on the primary path. Typical memory-harvesting pattern.

Verified against [aclanthology.org](https://aclanthology.org/2026.acl-demo.34/)

- [aclanthology.org](https://aclanthology.org/2026.acl-demo.34/)

A side-care agent rides alongside a primary agent chain, tapping its events without sitting in the critical path. It observes, logs, evaluates or enriches, a side-car, so the main flow stays unblocked while a second agent does cross-cutting work. It is the shape behind observability, guardrail and evaluation layers that must watch everything but block nothing. In anatomy terms it is a passive tap on the transport, with its own core.

## In the anatomy

A side-car reasoning core subscribes read-only to the primary chain's event stream; it does not sit in the request path; its own effectors handle logging, alerting or enrichment; the perimeter still gates any action it takes.

## At a glance

| Field | Value |
| --- | --- |
| Pattern | Sidecar (parasitic tap) |
| State model | session |
| Example | Mem0 / Zep sidecars· Letta background observers |

## Common use cases

## Strengths

## Weaknesses

## Basis

Description, use cases and trade-offs: Field Book analysis, synthesised from established agent-architecture literature.

## Verified against

- [https://aclanthology.org/2026.acl-demo.34/](https://aclanthology.org/2026.acl-demo.34/)

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