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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false. The description adds useful behavioral context: it automatically applies the 2026 $24,500 limit and catch-ups, and produces a year-by-year projection. This goes beyond the annotations by specifying built-in rules and output granularity.

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 efficiently packed sentences: the first states purpose and key features, the second gives a reference URL. No filler and the core function is front-loaded.

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?

For a 9-parameter calculator with no output schema, the description covers purpose, key built-in rules (2026 limit, catch-ups), and output granularity ('year by year'). It omits explicit return format details (e.g., table vs. summary), but annotations already cover the safety profile, making this largely complete.

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 100%, so the schema fully documents all nine parameters. The description mentions some inputs ('match, raises and returns') but adds no syntax, format, or inter-parameter details 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?

States a specific verb and resource ('project your balance at retirement') and names the key domain features (match, raises, returns, 2026 limit, catch-ups). The 401k focus distinguishes it from generic siblings like retirement_calculator.

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?

Implied usage is clear from the 401k-specific description, but there is no explicit when-to-use guidance, no mention of prerequisites, and no reference to alternatives such as retirement_calculator or roth_ira_calculator.

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