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

No annotations are supplied, so the description carries the burden, and it does disclose the key trait that this reference is free (no credit cost) and that it describes a POST endpoint rather than calling it. It does not state whether the returned reference is static or reflects live available series, nor anything about rate limits or response size. For a zero-parameter read-only help tool the burden is light, so a 3 is fair.

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?

A single sentence that front-loads the purpose ('Free reference for custom calculations') and then lists contents, with zero filler. The parenthetical operation list is long but each item is informative rather than redundant. Minor cost: the enumeration makes it dense to scan.

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 zero-parameter, read-only help tool with no output schema, the description adequately previews what the caller gets back — series availability, operation catalog, size tiers, and an example spec. The only real gap is that it does not say how the result should be used next (e.g., feed the spec into the compute endpoint), but nothing essential for calling it correctly is missing.

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?

The tool takes zero parameters, so the baseline is 4 and there is no parameter meaning for the description to add. The description correctly avoids inventing inputs and instead frames the tool as a static reference lookup.

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 concrete resource — a free reference document for custom calculations — and enumerates its contents (available series, operation list, size tiers, example request spec for POST /api/v1/btc/compute). An agent can tell this is documentation/help rather than a data-fetching endpoint, which separates it from data-oriented siblings like btc_free_preview or btc_snapshot_endpoint. It stops short of explicitly contrasting itself with those siblings.

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?

Usage is only implied: an agent must infer that this is the tool to call before constructing a custom compute request, since it supplies the operation list and an example spec. There is no explicit 'call this first when...' statement and no exclusion or named alternative. The word 'Free' hints at a cost distinction versus paid endpoints but does not spell out the routing rule.

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