Okta、MCPのスコーピングでAI エージェントのトークンコスト削減を提案

Okta says identity-scoped Model Context Protocol (MCP) tool lists can reduce AI agent token costs.

Each model call made by an AI agent can include schemas, names, descriptions and parameters for every tool exposed by a MCP server. Okta calls the resulting prompt overhead the “tool tax”: tokens consumed as a model considers tools, including those it will never call.

The company argues that this cost appears before an agent attempts a tool call. A later rejection of an unauthorised request therefore cannot recover prompt tokens already consumed. Okta’s proposed control filters the list of tools before it reaches the model, using permissions assigned to an agent identity and the user associated with it.

Okta’s internal modelling found that some permission scenarios reduced the number of visible tools by more than 90%. The company said tool-schema costs fell by roughly the same proportion, although it did not provide absolute token or dollar figures.

MCP tool schemas create prompt overhead on every turn

MCP servers have become a route for connecting AI agents to tools and data. Okta cites connections to Google Workspace, Slack and internal MCP servers as examples. An MCP server can expose a large number of tools, and the model receives a representation of each available tool in its prompt on every turn.

That representation includes a schema. It also includes the tool name, description and parameters.

Okta says the cost compounds when a widely used MCP server exposes many tools. Each active user incurs the prompt overhead whenever their agent makes a model call. The company frames this as both a tool-count problem and a user-count problem.

The issue also has an access-control dimension. An agent that sees tools outside its authorisation scope can attempt to use them. A control that rejects the call at runtime can block execution, though the model has already received the tool definition and used tokens to process it.

Okta filters tools before the agent prompt is built

Okta positions the capability within its “blueprint for the secure agentic enterprise”, which asks organisations to identify their agents, their permitted connections and their authorised actions.

Its approach narrows the connection question from access to a whole MCP server to access to individual tools on that server. An administrator configures the tools that a particular identity may use in the Okta dashboard. Okta then returns the scoped tool set instead of the server’s full catalogue.

The agent receives this shorter list in its prompt for each turn. Okta says it checks scope again at runtime before a tool call executes.

This design applies least-privilege access at the tool level. The company says an agent should not be aware of resources, databases or tools that it has not been expressly authorised to use. Removing unavailable tools from the prompt also removes their schema cost from the model call.

Okta does not describe a live customer deployment in the post. Its evidence for the claimed reduction comes from internal modelling using Okta product data and public vendor documentation, with no customer data used.

Internal model used OAuth scopes and representative roles

Okta modelled a single MCP client with access to a catalogue of enterprise tools. It compared the number of tools visible to the model before and after identity-based scoping.

To estimate scoped exposure, the company mapped Okta MCP Server tools to the OAuth scopes that unlock them. It then defined representative user segments. These included helpdesk read-only users and helpdesk operators.

Other segments were app administrators, brand and email administrators, and super administrators. Okta weighted each segment according to an assumed share of monthly traffic.

The company calculated tool-count reduction as one minus the ratio of scoped tools to unscoped tools. It said some scenarios removed more than 90% of visible tools. Its post states that tool-schema token cost tracks tool count nearly linearly because each tool contributes its name, description and parameter schema to every prompt.

Okta says actual results vary according to the tool catalogue, distribution of permissions and model selected. Average schema size, request volume and model pricing also affect absolute token and dollar costs.

Okta contrasts identity entitlements with gateway spending controls

The post distinguishes identity-based scoping from gateway controls. Okta says gateways can cap spending by key, team or group, and can support routing and rate limiting.

A gateway can meter tokens entering and leaving a system, as well as dollars spent. Okta says those controls can limit costs after a model decision becomes expensive.

Identity entitlements provide a different input. Okta says per-user and per-agent entitlements can determine the tools available to a specific agent or the person behind that agent, rather than applying access information at group level.

Paul Webber, Principal Cybersecurity Industry Analyst at Software Analyst Cyber Research, said: “Cost control for agents is best provided using identity governance tools that offer more granular control and precision without disrupting business processes.

“Okta’s approach is an elegant way to do this because it leverages the same entitlement data that governs security, not a separate metering layer without that insight.”

Okta’s account presents the gateway as a control for what passes through it. The identity layer filters the available tool set before those tools need to be metered.

Tool visibility also affects MCP attack exposure

The post ties the same mechanism to security exposure. Okta says removing tools from an unauthorised identity’s view also removes actions that identity could take if it were compromised.

Its proposed scope check operates at two points. The first occurs as the tool list is assembled for the agent prompt. The second occurs when the agent attempts to execute a tool call.

Okta describes the result as a smaller blast radius for a compromised identity. The remaining exposed tools determine the set of actions available to that identity. In the company’s model, the prompt contains only tools associated with the identity’s authorised OAuth scopes.

For organisations assessing MCP access, tool inventory and entitlement mapping are the main operational inputs. Okta’s methodology maps MCP Server tools to the OAuth scopes that unlock them, then compares the full tool catalogue with the scoped catalogue visible to each representative user segment.

Okta is a key sponsor of this year’s AI & Big Data Expo Europe held in Amsterdam on 19-20 October 2026.

See also: Meta Muse Glimmer brings local AI agents to consumer GPUs

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