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

The annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds useful behavior beyond that: the merge is shallow, overwritten keys are reported, and inputs are not mutated. It does not explain merge precedence or nested-object replacement in detail, but it gives meaningful behavioral context.

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?

The definition is a single front-loaded sentence with no filler. Every phrase contributes to purpose, scope, or the non-mutating constraint.

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?

The tool is simple, and the annotations cover its read-only nature, but there is no output schema and the description only loosely indicates return content. It does not fully specify whether the merged preview is returned alongside overwritten keys, nor how nested objects behave under a shallow merge.

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 description coverage is 0%, so the schema gives only types, not meanings. The description partially compensates by indicating that a shallow merge occurs and that keys are overwritten, which implies how base and updates relate, but it does not explicitly name the parameters or state which side wins in a collision.

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?

The description states a specific verb and resource: 'Preview a shallow merge' and adds the key behavioral result, 'report overwritten keys.' It also distinguishes the operation from a mutating merge by saying 'without mutating inputs.'

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?

The word 'Preview' and the phrase 'without mutating inputs' imply this is for non-committal merge checks before applying changes. However, there is no explicit when-to-use guidance, no when-not-to-use guidance, and no named alternative tool for comparison.

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