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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds that data is historical/quarterly and gives the backing REST endpoint (GET /stock/earnings), which is modest extra context, but it says nothing about ordering guarantees beyond what the schema's limit param implies, rate limits, or coverage/emptiness behavior.

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?

Two short sentences, front-loaded with the data scope. The REST endpoint fragment is arguably redundant for an agent but is brief and harmless; nothing else is 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?

For a simple two-parameter read tool with full schema coverage and a readOnly annotation, the description plus schema is nearly sufficient. The only real gap is that no output schema exists and the description only loosely sketches the return shape ('actual vs. estimated EPS by period'), and it omits sibling differentiation.

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 both 'symbol' and 'limit' are already well documented (ticker example, most-recent-first ordering, bounds). The description adds no meaning beyond that, which is the expected baseline when the schema carries the load.

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: 'Historical quarterly EPS surprises — actual vs. estimated EPS by period.' It is clear what data comes back, but it never names or contrasts itself with the closest sibling, finnhub_earnings_calendar, so the agent must infer the difference between historical surprises and an earnings calendar.

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 explicit when-to-use guidance, no exclusions, and no mention of alternatives. The word 'Historical' implies past-data lookups, but nothing tells the agent when to prefer this over finnhub_earnings_calendar or finnhub_basic_financials.

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