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Building a Production Tool Registry

Design and maintain a central catalogue of agent tools — versioning, capability tagging, and dynamic discovery for scalable agent systems.

By Amit UpadhyayPublished 24 MayUpdated 11 Sep 202611 minArticle 1 of 12 in Agentic Systems

A central tool registry stores versioned tools with owners and side-effect classes; just-in-time selection exposes only a handful of relevant schemas to the agent, and risky tools require approval.

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The idea at a glance

The problem

When

Many teams build tools for shared agents, and the tool count keeps growing

The obvious move

Each team adding tools straight into the agent’s code

Fails because

Nobody knows who owns a tool, a schema change breaks agents without warning, and the agent cannot tell a read from a refund

The fix

Tool registry works by

A registry that records each tool’s owner, schema version and side-effect class, and selects a small relevant set for each request

At the cost of

A registry service or package to run, and review when tools are added or changed

The scenario every mode follows

“Refund order 48213 and email the customer a confirmation.”

A company assistant with tools from six teams: billing, orders, HR, IT, sales and support
120 registered tools
claude-sonnet-5-5

Where the obvious approach breaks

120 tools, 6 teams, no owners

If you let every team add tools directly to the agent.

When the billing team renamed `amount` to `amount_cents` in their refund tool, the agent kept sending dollars, refunding a hundredth of the intended amount for two days. Nobody else knew the tool had changed, or who to ask.

Helps to know firstFunction calling

Tools Need Owners, Versions and Rules

The naive approach to giving an LLM tools is "dump every JSON schema into the system prompt and hope for the best." This breaks at ~20 tools (context bloat, latency, hallucinated tool calls) and again at ~100 (cost, security boundaries, multi-tenant scoping). A tool registry is the runtime indirection that turns "a bag of functions" into "a versioned, scoped, observable capability catalogue".

If tools are piling up

Your system prompt is 8 KB of tool schemas and growing
You can't answer "which agents have access to the delete-user tool?"
Tools have side-effects but no idempotency keys and no per-tenant scoping

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