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MCP Payload Optimization Policy

Policy Name

MCP Payload Optimization Policy

Summary

Optimizes MCP tool responses for token consumption by transforming HTML to Markdown and removing unnecessary data

Category

MCP

First Flex Gateway version available

v1.12.0

Returned Status Codes

No return codes exist for this policy. The policy modifies response bodies and doesn’t block traffic based on content.

Summary

The MCP Payload Optimization policy reduces LLM token consumption by transforming MCP tools/call responses before they’re returned to the client.

Configure the transformations to:

  • Convert HTML to Markdown.

  • Remove base64-encoded data.

  • Remove JSON fields with null values.

  • Remove excessive whitespace.

The policy processes responses when:

  • The upstream response has Content-Type application/json or text/event-stream (SSE).

  • The body is a JSON-RPC MCP tools/call result (including streamed SSE events that carry those results).

Configure the minimum response size to skip transformation for small payloads.

The policy uses the pre_transform_tokens and response_tokens for tool metrics to estimate token reduction.

Configuring Policy Parameters

Flex Gateway Local Mode

The MCP Payload Optimization policy isn’t supported in Local Mode.

Managed Flex Gateway and Flex Gateway Connected Mode

When you apply the policy from the UI, the following parameters are displayed:

Element Description Default

HTML to Markdown

Converts HTML content in tool results to Markdown.

Enabled

Strip Base64

Detects and removes base64-encoded data from tool results.

Enabled

Remove Nulls

Removes JSON fields whose value is null.

Disabled

Collapse Whitespace

Removes excess whitespace in text content.

Enabled

Min Response Size (bytes)

Minimum response size in bytes to transform. Smaller responses pass through unchanged. Minimum value is 0.

500

Per-Tool Overrides

Overrides the policy configuration values for specific tool names. Tools without an override use the global policy configuration. To learn more, see Per-tool overrides.

N/A

Per-tool overrides

Use Per-Tool Overrides to overide the the response optimization of specific tools. For example, if whitespace is necessary for a specific tool response but not for others, override Collapse Whitespace for that tool.

You can override the global policy configuration for the HTML to Markdown, Strip Base64, Remove Nulls, and Collapse Whitespace parameters but for not Min Response Size.

If you omit a parameter in an override configration, the tool uses the corresponding value from the global policy configuration.

See Also