Tool Registry

A tool registry is the catalogue an agent consults to learn what actions exist: each entry pairs a name and description with a parameter schema, and behind it, the code that actually runs. Function calling is the mechanism by which a model asks for a tool; the registry is what decides which tools it is allowed to ask for at all, and it is usually where authorisation, versioning and rate limits live too. Keeping it as a first-class component rather than a hard-coded list matters for three reasons. Tools change independently of prompts, so a registry lets you add, deprecate or repair one without editing every agent that uses it. Different agents and different users should see different subsets — a support agent and a billing agent do not need the same permissions, and least privilege is far easier to enforce at a registry than inside prompt text. And the description strings in a registry are not documentation; they are part of the prompt, so the wording of a tool's description directly determines how often the model reaches for it, and vague descriptions are a common cause of an agent using the wrong tool. The other reason to centralise is size. Every exposed tool consumes context and adds a candidate the model can choose wrongly, and accuracy tends to fall as the list grows. Registries therefore commonly present a filtered set per task rather than everything available, which is a retrieval problem in its own right.