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

With no annotations, the description carries the full burden, and it does disclose the most important behavioral trait: this only builds a URL, implying no network call or side effects. It omits whether a paid key/credits are required to use the resulting URL, whether the URL is validated, and what type is returned, all of which matter for a 'paid' endpoint helper.

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 core purpose and packs the parameter constraints without filler. It is dense but readable, with only a minor cost in that the parameter clauses run together rather than being separated.

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 three-parameter, zero-annotation, no-output-schema tool, the description covers the parameter semantics but leaves gaps about the return value (presumably a URL string) and paid-tier prerequisites. It is adequate to call the tool but not fully self-contained.

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 0%, and the description compensates well: it enumerates allowed granularity values (minute/hour/day) not present as an enum in the schema, gives the valid hours range (1..17520), and clarifies that 'source' is an optional venue filter. It does not mention the 24-hour default or whether an absent source means all venues.

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?

Uses a specific verb ('Build') and resource ('paid history URL'), making clear this constructs a URL rather than fetching data. It does not, however, distinguish itself from siblings like btc_market_endpoint or btc_snapshot_endpoint, so an agent must infer which history/market/snapshot variant applies.

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: 'paid history' hints this is the paid tier counterpart to the free preview siblings, but there is no explicit when-to-use or when-not-to-use statement and no named alternative. The agent gets the context but must reason about routing itself.

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