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The Tool Hub is the central orchestration layer of Char. It’s a Cloudflare Durable Object scoped to each user within your organization, aggregating tools from all connected sources into a unified registry.

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Why Tool Hub Matters

Traditional integrations require building point-to-point connections between applications. Want your CRM to talk to your ERP? Build an integration. Add a ticketing system? Another integration. This scales poorly. The Tool Hub inverts this model:
  1. Each application registers tools with the user’s Tool Hub
  2. The Hub maintains a unified tool registry
  3. Any connected client can invoke tools from any registered source
The result: cross-site RPC—previously impossible without massive integration projects—becomes function calls mediated by policy.

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Architecture

Each browser tab with Char embedded maintains a WebSocket connection to the same Tool Hub instance. Tools from all tabs appear in a unified registry, namespaced by domain to avoid collisions.

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Identity Scoping

Every Tool Hub instance is scoped to a unique combination of:
  • Organization ID — Your Char organization
  • User ID — The authenticated end user (from JWT sub claim)
This means:
  • Each user has their own isolated Tool Hub
  • Cross-tenant access is structurally impossible
  • There is no code path that could query another user’s data

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Tool Namespacing

When tools are registered from different domains, the Hub namespaces them to avoid collisions:
DomainToolNamespaced As
crm.company.comupdateLeadcrm.updateLead
erp.company.comlookupInvoiceerp.lookupInvoice
mail.company.comsendEmailmail.sendEmail
The agent sees all available tools and can orchestrate workflows that span applications.

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MCP Server Surface

The Tool Hub itself exposes an MCP server interface. This enables:
  • Claude Desktop connecting to your Tool Hub
  • VS Code extensions accessing the unified tool surface
  • Cloud automation workers executing workflows
Any MCP client that authenticates to your Hub can invoke browser-based tools across all your open tabs.

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Policy Enforcement

The Tool Hub enforces policy before tool execution:
  • Tool classification — read / write / exfil categories
  • Approval workflows — configurable per classification
  • Role-based visibility — tools scoped by user role
  • Kill switch — instant tool/provider disablement
See Context Isolation for how this provides defense against prompt injection.

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What This Enables

With the Tool Hub, you can:
  1. Cross-app workflows — “Pull invoice status from ERP and add to this CRM record”
  2. Unified agent experience — One conversation that spans all your applications
  3. External client access — Claude Desktop can invoke browser tools
  4. Centralized audit — Decision traces for every tool invocation

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Further Reading

Cross-App Tools

How tools work across applications

Deployment Tiers

Progressive adoption from page-scoped to enterprise

Context Isolation

Security model and prompt injection defense

Session Inheritance

Why no new OAuth flows are required