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

Annotations already provide readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description reinforces these by stating 'Every call is read-only and idempotent, so after correcting the input it is always safe to retry.' It also adds the error return behavior, which is not covered by annotations. The mention of 'FREE' is extraneous, but overall the description adds meaningful context beyond the 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?

The description is approximately 120 words, highly focused, and front-loaded. The first sentence states the primary purpose. Each subsequent sentence adds distinct value: defaults, example, usage guidance, error handling, and safety. No redundant or unnecessary wording.

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 tool's moderate complexity (4 parameters, 1 required, full schema coverage, output schema present, rich annotations), the description covers purpose, usage differentiation, error behavior, idempotency, and provides a concrete example. It addresses all key aspects an agent needs to correctly invoke the tool, leaving no obvious gaps.

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 coverage is 100%, so the input schema already documents all parameters with descriptions and defaults. The description adds a typical input example and mentions the '50/30/20 rule', which provides context but does not significantly enhance understanding beyond what the schema already provides. Baseline 3 is appropriate.

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 clearly states the verb 'split' and the resource 'monthly income', and provides a concrete example of the output format. It also explicitly distinguishes itself from the sibling tool 'savings_goal' by stating 'Not for how long a target takes to reach (savings_goal)'. This leaves no ambiguity about the tool's purpose.

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 description explicitly says when to use the tool ('Use when monthly income needs allocating across buckets') and when not to use it, naming the specific alternative ('savings_goal'). It also provides error handling guidance, stating that the tool never raises protocol errors but returns a structured error object, which helps the agent decide to retry after correcting input.

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