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

Annotations only declare the generic profile (not read-only, not idempotent, closed-world), while the description supplies the operationally important behavior: the preview writes nothing, preview_mismatch semantics, default-portfolio fallback, ambiguity handling, and a scope boundary ('does not trade, record holdings or move money'). That is substantial context beyond what annotations convey.

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 purpose and the preview-then-confirm rule are front-loaded and every sentence carries an operational rule. It is dense, however: the mid-paragraph instruction about relaying summary_line, message, grouped outcomes and portfolio_count is presentation scripting that makes the description longer than the invocation contract strictly requires.

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 two-phase, stateful, partially irreversible batch write, the description covers gating, error recovery, defaults, ambiguity policy and scope exclusions, and an output schema exists so return values need not be re-explained. An agent has everything needed to drive both calls correctly.

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 baseline is 3, but the description adds workflow meaning: how confirm, preview_id and confirmed_indexes interlock across the two calls, and what happens when portfolio_id/portfolio_name are omitted. Some of this (default portfolio, preview_id required when confirm=true) duplicates the schema, so it falls short of fully additive.

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 opening sentence states a specific verb and resource with explicit scope: add up to 100 company rows to one StockLens portfolio via a two-call preview/confirm flow. The batch scope plus the 'up to 100 rows' limit inherently separates it from the single-entry sibling add_to_watchlist, so an agent can select it correctly without opening the schema.

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?

It prescribes exactly when to call with confirm=false (preview only, nothing added) versus confirm=true (adds confirmed_indexes from preview_id), and how to recover from failure states ('a changed list or a different portfolio needs a new preview; preview_mismatch means the preview expired'). It also gives exclusion rules — never pick an ambiguous listing for the user, only add a not_covered row if asked — leaving almost nothing to inference.

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