fits_header

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

Annotations already establish readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds useful context: the output includes raw header cards plus a parsed frame record stored elsewhere, and that no PixInsight session is required. It does not go deeper into things like encoding, error conditions, or limits, but for a simple read-only tool this is reasonable.

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?

The description is a single, compact sentence with no filler. It front-loads the main output and adds the important 'no PixInsight needed' qualification without redundancy.

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 tool with one parameter knob, strong read-only annotations, and a clear output statement, the description covers the essential decision and invocation context. It explains what the caller receives and hints at the non-PI prerequisite. A slightly more explicit statement about 'path' being a filesystem path would make it complete.

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%, so the description must compensate for the undocumented 'path' parameter. It clarifies that the parameter refers to a single file whose header cards will be returned, which is helpful. It does not specify path format, file type validation, or whether directories are acceptable, leaving some ambiguity.

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 identifies the resource ('Raw FITS header cards of one file') and the second output ('the parsed frame record'), making the tool's purpose clear. It lacks an explicit verb like 'get' or 'read', but the meaning is unambiguous. It does not explicitly distinguish itself from siblings such as image_keywords, though 'no PixInsight needed' hints at a key difference.

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 phrase 'no PixInsight needed' implies this tool is appropriate when the caller wants FITS header data without running a PixInsight session. However, it does not explicitly state when to prefer this over sibling tools like image_keywords or when not to use it. The guidance is present but largely implied.

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