Unflatten messages[] (in memory)

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations declare readOnlyHint=true and idempotentHint=true. Description reinforces with 'purely functional — no disk, no network, input never mutated.' Also details behavior for missing markers. Fully transparent and consistent with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, no wasted words. First sentence defines the core function, second adds important caveats. Perfectly front-loaded and concise.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the straightforward nature of the tool, the description covers the restoration process, marker handling, and principles (functional, idempotent). Output schema exists (as per context signal), so no need to detail return values. Comprehensive for the task.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema descriptions provide clear definitions for both parameters (messages and extracted). The tool description adds behavioral context about the marker format and byte-for-byte restoration, enhancing understanding beyond schema. With 100% schema coverage, baseline is 3, but the additional context merits a 4.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Clearly states it restores a conversation flattened by flatten_messages, re-inlining tool_result markers byte-for-byte. The verb 'restore' and resource 'conversation' are explicit. Distinguishes from sibling tools like flatten_messages by directly referencing the inverse operation.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Implicitly specifies usage: use when you have a flattened conversation and want to restore it. Does not explicitly state when not to use or list alternatives, but the context of being the inverse of flatten_messages is clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.