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

Annotations already declare the write/destructive/non-idempotent profile, so the bar is lower, and the description still adds real value: it discloses the upsert behavior and, critically, that omitted fields are cleared ("clearing either one left out"). The only quibble is a slight tension with idempotentHint=false, since a replace-or-add of the same payload yields the same state, but the description is not contradicting the annotation outright.

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?

Three short sentences with zero filler; the core write/upsert behavior leads, followed by the two field caveats. Nothing is repeated from the schema or annotations.

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 6-parameter mutation with no output schema and very low schema coverage, the description covers the upsert and clearing semantics plus two field meanings, which is the most important information. It still omits exchange/collectionId semantics and any auth or error behavior, so it is adequate but with clear 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 only 17% (just teamId is documented), so the description should carry more. It does add meaning for quantity (portfolio-only) and note (short label, not research), but leaves exchange — a semantically ambiguous field that affects how a holding is matched — and collectionId entirely unexplained.

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 ("Writes one item to a team collection") and immediately clarifies the upsert scope: adds the symbol or replaces the quantity/note of an existing entry. This is clearly distinguishable from sibling read tools (collections.get, collections.list) and from collections.remove_symbol, without needing to name them.

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?

Usage is implied by the semantics: use this to add or update a single collection item, and "Quantity only applies to portfolios" scopes one field's applicability. The line "The item note is a short label, not research" implicitly routes research content elsewhere (e.g. notes.save), but no alternative is named and there is no explicit when-not-to-use or prerequisite guidance.

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