list_sources

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

Annotations already declare readOnly/idempotent, so the remaining value is cost and prerequisites, and the description delivers both: 'Free to call (does not use the API allowance)' and a note that it reports whether provider credentials are needed and configured. That is exactly the kind of context annotations cannot express. It does not state pagination or ordering behavior, keeping it at 4.

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 dense sentence, front-loaded with the verb and resource, and every clause carries information (formats, fields, credentials, cost). The enumeration is long but none of the items is filler.

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 discovery tool with a full output schema, the description covers purpose, cost, and credential prerequisites, which is nearly everything an agent needs. The only gap is an explicit instruction on when to prefer this over calling get_timeseries directly.

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 there is nothing for the schema to document and the baseline is 4. The description still uses the space usefully by explaining that some sources have source-specific parameters, which prepares the agent for what the output will contain.

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?

Names a specific verb+resource ('List the AuraStream data sources') and then enumerates exactly what the listing contains: coverage, ticker format, intervals, dtypes, optional source params, non-OHLCV fields, and credential status. That is far more specific than siblings get_timeseries/get_latest, which retrieve data rather than describe it.

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?

The subject matter makes the when-to-use clear (discover sources, formats and credential requirements before fetching), and being a zero-parameter catalog it has no per-call conditions to state. It does not explicitly say 'call this before get_timeseries' or name the alternatives, 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.