Voice DNA runtime block

Also called: runtime block, runtime_block_json

A Voice DNA runtime block is a compact, machine-readable rendering of a writing profile, formatted to be loaded directly into a language model's system prompt so an agent can adopt a person's voice without a human pasting instructions.

It is the profile in the shape a system prompt can consume, rather than the shape a human reads.

A writing profile has two audiences. A human reads the long-form report to understand their own patterns. A model needs the same information compressed, unambiguous and positioned where system instructions go. The runtime block is the second rendering.

The practical consequence is agent-native delivery. Because the block is data rather than prose, an agent can fetch it over an API or MCP tool call and install it, so the person's voice follows them into automations they never open a chat window for.

RenderingAudienceShapeWhere it is used
Writing Style Profile reportThe authorLong-form prose with examplesReading, reviewing, editing your own patterns
Runtime blockA language modelCompact structured block, mode-slicedSystem prompt, agent config, MCP tool response
Two renderings of the same writing profile

Frequently asked questions

Why not paste the full profile report into the system prompt?
Length competes with the task. A long prose report spends context on explanation the model does not need and dilutes the instructions it does. The runtime block keeps the constraints and drops the exposition.
What does mode slicing mean in a runtime block?
One author writes differently in an investor update and a Slack reply. Mode slicing means the block carries more than one register, and the caller selects the slice that matches the medium and audience rather than averaging them.
Can an agent retrieve a runtime block without a human?
Yes, where the profile provider exposes one. MyWritingTwin serves runtime_block_json through its MCP server, so an agent with credentials can install a principal's voice as part of its own setup.

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MyWritingTwin. “Voice DNA runtime block.” Last updated 2026-09-15. https://www.mywritingtwin.com/glossary/voice-dna-runtime-block