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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes well beyond them: it states the band carries no directional information, is symmetric about the last close by construction, and that the system suppresses the deck when calibration is unmeasured. These are non-obvious behavioral facts an agent could not infer from structured fields.

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?

It is front-loaded with what the envelope contains, then the directional caveat, then the calibration caveat. Dense but nearly every clause earns its place; the 'there is no side, no median… say so, and never turn it into up/down' passage is mildly repetitive but justified for a financially sensitive output.

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, the description carries the full burden of describing return values, and it does — magnitude band in ATR terms, odds at 0.5/1/2 ATR over 6/12/24 bars, and calibration fields (ece, n, coverage). Combined with annotations covering the safety profile, an agent has everything needed to call and interpret it.

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%, with enums for market and tf and a documented `at` semantics, so the schema does the heavy lifting. The description only obliquely reinforces the `at`/timeframe scoping ('by a given time'); it adds no syntax or format detail beyond the schema.

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 description names a specific, self-contained resource — 'the envelope the forecast sidecar had issued for one market and timeframe by a given time' — and immediately scopes it (band, odds, calibration). No sibling tool in the list exposes this resource, so an agent can route to it 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?

There is strong interpretive guidance (treat unmeasured/uncalibrated bands as untrusted, never convert the output into up/down), but nothing about when to call this versus alternatives such as tape, chart_state, or strategy_quote. Usage context is implied by the resource, not stated.

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