diff --git a/AGENTS.md b/AGENTS.md
index 6413f3e7cb..eb372f9215 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -50,6 +50,11 @@ Use ESM TypeScript, two-space indentation, and Prettier defaults. Keep compiler
 
 Start from the analyst question and desired result, not a provider API. Before adding a tool, inspect the existing contract and its nearest alternative.
 
+- Prefer reusable, composable primitives: inspect one explicit object or
+  relationship and return evidence that can support different analyst
+  questions. Compose primitives into a workflow only for a recurring outcome
+  that benefits from joining evidence sources; keep one-application or
+  business-domain interpretations out of general tool contracts.
 - Use **inspect/search** tools for facts about a target or candidate set; use **trace** tools for relationships; use **compare** tools for explicitly paired inputs.
 - Add a **workflow** when observed agent use shows a repeated sequence that REA can compose without losing analyst control. Return useful results inline so callers can choose their next action.
 - Use **observe/capture/replay** only when runtime activity is required, and declare authority and lifecycle effects in the contract.
diff --git a/docs/tool-design.md b/docs/tool-design.md
index c04ab75a77..0000be0b44 100644
--- a/docs/tool-design.md
+++ b/docs/tool-design.md
@@ -20,6 +20,23 @@ protocol, authority, and resource-safety constraints, and report their effects.
 These are task shapes, not required prefixes. Name a tool for the action and
 object agents reason about; keep the name distinct from nearby alternatives.
 
+## Prefer primitives; compose workflows
+
+Start with a primitive when one call can report a reusable fact about one
+identified object or relationship, such as an instruction decode, a type
+layout, a reference, a dispatch target, or a resource graph. The same primitive
+should be useful across different applications or analyst questions. A
+format-specific decoder can still be a primitive when it describes a reusable
+format rather than one application's product behavior.
+
+Add a workflow when repeated analysis shows that callers need the same
+multi-source result and REA can join the evidence without hiding important
+choices or uncertainty. A useful check is whether the workflow remains
+meaningful for different applications that share the relevant evidence types.
+If its purpose depends on one application's business rules or product concepts,
+keep that interpretation outside the general tool contract and expose the
+underlying evidence through reusable primitives.
+
 ## Decide whether to add a tool
 
 1. State the user intent and the smallest result that answers it.