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

Annotations declare readOnlyHint=false, idempotentHint=false and openWorldHint=true, so the description is not carrying the whole burden, yet it still adds meaningful side-effect disclosure: the first follow in a sector creates an email subscription, and a plan tier is required. This goes beyond what the annotations state, though it doesn't clarify behavior on repeat follows or whether an existing subscription is modified.

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?

Compact – essentially one sentence with two parentheticals, no filler. The side-effect and plan conditions are packed in, though the two stacked parentheses make it slightly dense to parse.

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 7-parameter write tool with full schema coverage, no output schema and non-destructive annotations, the description covers the key behavioral facts (side effect, tier requirement). Minor gaps remain on repeated-follow behavior and per-type parameter usage, but nothing critical blocks correct invocation.

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 already documents all seven parameters (id, slug, type, sector, ticker, timezone, reminder_offsets) including which type each applies to. The description adds no syntax, format, or selection guidance beyond what the schema provides, so baseline 3 applies.

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 (Follow) plus the three resource kinds it accepts (stock, asset, calendar item), so an agent can distinguish it from siblings like sectors_unfollow and sectors_follows. The parenthetical about the sector email subscription adds scope context but the phrasing is somewhat cramped.

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?

Provides a real prerequisite ('needs the starter plan or above') that gates usage, which is useful. However, it offers no explicit when-to-use versus when-to-unfollow or when to prefer a listing tool; the distinction from sectors_unfollow/sectors_follows is only inferable from the names.

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