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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world), so the bar is lower. The description adds genuinely non-derivable behavior: a hard 200-chunk ceiling, offset-bearing output, surrogate-pair-safe boundaries, and the fact that no key, credits, or wallet are required. It does not explain chunk-boundary policy or defaults, which keeps it from a 5.

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?

Front-loaded with the core action and short overall, with no filler sentences. The three clipped fragments about free mode are slightly redundant with each other, but they are informative rather than wasted.

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?

An output schema exists, so return values need not be described, and the description instead covers constraints, auth/pricing, and encoding safety. What remains missing — default overlap/maxChars values and boundary behavior — is minor for a straightforward text utility.

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 67%, so the schema documents some fields but not all semantics. The description implies overlap exists ('overlapping chunks') and that offsets are returned, but it never explains what maxChars controls, what the default overlap is, or how the 200-chunk cap relates to maxChars. That is baseline-level compensation, not more.

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 ('Split text') plus the concrete output shape (overlapping chunks with offsets, surrogate pairs intact) and the 200-chunk cap. No sibling tool does chunking, so there is no ambiguity to resolve — an agent can immediately tell this is the text-splitting utility.

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?

There is no statement of when to choose this tool, no prerequisites, and no alternative named. The only contextual hints are pricing ('FREE during validation') and 'existing source and input limits apply', neither of which tells the agent which situation calls for chunking.

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