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JustFill PDF Form Automation

by io.github.mrmaciej1
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Preview detected boxes

render_preview

Render a page with the field boxes drawn on it, to verify placement.

Blue = deterministic (template/AcroForm/agent), green/orange/red = ML
confidence bands (`>= 0.7`, `0.4`–`0.7`, `< 0.4`). Labels show field ids.
The result has the image and a `preview_url` link to the same image; some
clients (e.g. ChatGPT) do not display tool images, so there the user sees
the page only through `preview_url`. Also records the field-layout visual
review receipt for `page_index` required before `fill_pdf` or `save_template`
on ML-detected layouts.

When to use:
- Use `render_preview` to inspect empty field box positions, IDs, false
  positives, and missed inputs before filling or after modifying geometry with
  `add_field`, `update_field`, `update_fields`, `remove_field`, `remove_fields`,
  or `prune_fields`.
- Use `render_filled_preview` instead to see actual field values typeset inside
  those boxes and check for text overflow before calling `fill_pdf`.

Input Schema

NameRequiredDescriptionDefault
page_indexNo0-based page index (`0` to `page_count - 1`) to render with field bounding-box overlays.
workspace_idYesActive workspace ID returned by `open_pdf` (`summary.workspace_id`).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changed
    • addedInput schema / properties / page_index / description
      Added value: +"0-based page index (`0` to `page_count - 1`) to render with field bounding-box overlays."
    • addedInput schema / properties / workspace_id / description
      Added value: +"Active workspace ID returned by `open_pdf` (`summary.workspace_id`)."
  2. First observed

TDQS

A4.9/5.0
Behavior5/5

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

Goes well beyond the annotations by disclosing a side effect they don't cover: it records a field-layout visual review receipt for page_index that gates fill_pdf/save_template on ML layouts. It also explains the color-band legend and the client limitation where tool images aren't displayed, so the agent knows to surface preview_url.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core action, then legend, then return-value caveat, then a clearly delimited 'When to use' block. Every sentence carries operational information with no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description still explains the return (image plus preview_url) and its client-display caveat. The gating side effect, alternatives, and trigger conditions are all covered, leaving nothing an agent needs missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline is 3, but the description adds meaning: page_index is not just a render target, it is the page whose visual review receipt gets recorded and required downstream. workspace_id is left to the schema, which documents it adequately.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource (render a page with field boxes drawn) and immediately frames the goal (verify placement). It explicitly distinguishes itself from the sibling render_filled_preview, so an agent can route between the two without opening schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides an explicit 'When to use' section: inspect empty boxes before filling or after geometry edits via add_field/update_field/remove_field/prune_fields, and a named alternative (render_filled_preview) for value/overflow checks. The prerequisite for fill_pdf and save_template is also stated.

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

All JustFill PDF Form Automation toolsInspect
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