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

Annotations already establish readOnly/idempotent/non-destructive, and the description still adds real behavioral disclosure: the APPROXIMATE fallback when a heading isn't found, what that fallback span contains, and the highlight_url in the first lines for citation. That is context an agent cannot get from structured fields.

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?

Well front-loaded — size comparison and fallback caveat come before the arg list, which is the right order. Some prose ('That span contains the item if the filing has it: search within it') is slightly wordier than needed, but nothing is filler.

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 4-param read tool with an output schema, everything an agent needs is present: when to pick it, fallback behavior, and how to interpret the returned header lines. Return-value structure is correctly left to the output schema.

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 0%, so the description carries the full burden and does: accepted item formats ('1A', '7A', '2.02', '16G', or names), the 20-F remapping (Risk Factors in 3.D, MD&A as Item 5), part semantics with the bare-number default, and get_markdown's default and False meaning.

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+resource ('Read one Item of a 10-K, 10-Q, 8-K or 20-F') with concrete examples (Risk Factors, MD&A) and immediately distinguishes itself from get_document by size. An agent can tell exactly what this returns versus a whole-filing read.

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?

Explicitly frames the choice ('instead of the whole document'), quantifies the savings ('5-15% of the filing'), and routes non-applicable cases elsewhere: 'other forms have no Items: read them with search_document or get_document'. Alternatives and exclusions are both named.

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