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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower, and the description still adds real behavior: point-in-time clipping that prevents look-ahead bias, the 2007 history horizon, and a paywall (free keys get recent days, full history from $49/market). It doesn't discuss pagination or row limits, which keeps it from a 5.

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?

Front-loaded with the data scope, then the two calling modes, then the paywall note; each sentence carries information. Slightly dense and example-heavy, but the examples (ES, NQ, CL …) do real work for the root parameter.

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?

With no output schema and six parameters, the description should say more about what comes back (column set, whether open interest is a separate field) and about start/end range semantics. Coverage and paywall are well handled, but these gaps leave an agent guessing at the response shape.

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 67%, so baseline is 3. The description adds useful semantics beyond the schema for root (leading '/' tolerated, many examples) and the continuous-vs-contract interaction ('default true when no contract'), but it says nothing about start or end, the two undocumented parameters.

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 (daily OHLCV and open interest for futures) with unusually precise scope: 139 markets, named exchanges, coverage since 2007, individual contracts vs. continuous back-adjusted series. Any agent can tell this is the futures-bars tool and not the equity get_bars sibling.

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?

Explains the two invocation modes clearly — pass root for the continuous series, or contract (e.g. ESZ26) for a single contract — and notes that output is clipped to as_of. It never explicitly excludes alternatives (e.g. 'for equities use get_bars'), so it stops short of a 5.

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