Skip to main content
Glama

Cobalt Capture

by com.cobaltcapture
OverviewDiscussionsAdmin

replace_screenshot

Destructive

Overwrite one existing screenshot in a review with a new capture, in the same position. Destructive: the old image and any pins or annotations on it are removed and cannot be recovered; the title and comment change only if new ones are passed. Works on screenshots only, not notes. Takes the same capture arguments as add_screenshot, plus item, the 1-based number of the screenshot to replace.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
itemYesThe 1-based number of the existing screenshot item to overwrite (as it appears in the review, counting notes).
imageNoA small base64-encoded PNG, JPEG or WebP (data: URL prefix accepted). Intended for images under about 100 KB; larger screenshots are better uploaded and passed as image_url.
titleNoOptional short caption for the screenshot.
reviewYesThe review slug or URL from create_review.
commentNoOptional note describing what this screen shows or what's wrong with it.
page_urlNoA public http(s) page for Cobalt to render and screenshot server-side. Pages behind a login can't be rendered. Becomes the item's source_url unless one is passed. Takes 10 to 30 seconds; a site that blocks automated browsers returns an error.
viewportNoWith page_url: 'desktop' (1280x800, default) or 'mobile' (390x844 phone, 2x, touch).
full_pageNoWith page_url: capture the entire scrollable page instead of the first viewport. Default false. Pages that scroll inside an inner container come back viewport-sized.
image_urlNoAn image URL on Cobalt's own image host, as returned by https://cobaltcapture.com/api/upload (multipart field `file`, returns {url, key}) or by the editor's window.cobaltGrab(). External URLs are refused.
source_urlNoOptional URL of the page the screenshot was taken on.
claim_tokenYesThe claim_token from create_review (authorizes the write). For a review the human has SAVED to their account, pass the agent token they generated on the review page (Export & more → Hand to your agent) here instead.
hide_selectorsNoWith page_url: extra CSS selectors to hide before the shot, e.g. ['#newsletter-modal', '.chat-widget']. Common cookie and consent banners are hidden on every render.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed6 schema fields changed
    • changedInput schema / properties / full_page / description
      Previous value: -"With page_url: capture the entire scrollable page instead of the first viewport. Default false. Prefer the fold first; use full_page for one overview shot. Sites that scroll inside an inner container (some app-style marketing pages) come back fold-sized regardless — if that happens, say so rather than retrying."New value: +"With page_url: capture the entire scrollable page instead of the first viewport. Default false. Pages that scroll inside an inner container come back viewport-sized."
    • changedInput schema / properties / hide_selectors / description
      Previous value: -"With page_url: extra CSS selectors to hide before the shot (e.g. ['#newsletter-modal', '.chat-widget']) when the returned image shows something still covering the page. Common cookie/consent banners are already removed on every render."New value: +"With page_url: extra CSS selectors to hide before the shot, e.g. ['#newsletter-modal', '.chat-widget']. Common cookie and consent banners are hidden on every render."
    • changedInput schema / properties / image / description
      Previous value: -"For SMALL images only (< ~100 KB) that you already hold as base64 text: a base64-encoded PNG/JPEG/WebP (data: URL prefix accepted). Not the path for screenshots — emitting one as tool-call text is slow and error-prone, and an image you received as an image cannot be transcribed. Upload it and pass image_url instead."New value: +"A small base64-encoded PNG, JPEG or WebP (data: URL prefix accepted). Intended for images under about 100 KB; larger screenshots are better uploaded and passed as image_url."
    • changedInput schema / properties / image_url / description
      Previous value: -"The image URL returned by Cobalt's own upload: POST the file as multipart field `file` to https://cobaltcapture.com/api/upload (returns {url, key}) — ideally from inside the script that captured it — or use the browser hook window.cobaltGrab(). Must be on Cobalt's own image host; external URLs are refused."New value: +"An image URL on Cobalt's own image host, as returned by https://cobaltcapture.com/api/upload (multipart field `file`, returns {url, key}) or by the editor's window.cobaltGrab(). External URLs are refused."
    • changedInput schema / properties / page_url / description
      Previous value: -"A public http(s) page for Cobalt to render and screenshot server-side — the path when you have no browser or screenshot tool of your own (chat clients, text-only agents). Public pages only: nothing behind a login you signed into in your own session. Becomes the item's source_url unless you pass one. Takes 10–30 s (bot checks are waited through); a site that hard-blocks automated browsers returns a clear error — report that as a coverage gap, don't retry."New value: +"A public http(s) page for Cobalt to render and screenshot server-side. Pages behind a login can't be rendered. Becomes the item's source_url unless one is passed. Takes 10 to 30 seconds; a site that blocks automated browsers returns an error."
    • changedInput schema / properties / viewport / description
      Previous value: -"With page_url: 'desktop' (1280x800, default) or 'mobile' (390x844 phone, 2x, touch) — the way to test the phone fold."New value: +"With page_url: 'desktop' (1280x800, default) or 'mobile' (390x844 phone, 2x, touch)."
  2. Added

TDQS

A4.7/5.0
Behavior5/5

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

Annotations declare destructiveHint=true, but the description goes further: the old image plus any pins or annotations are removed and 'cannot be recovered,' and title/comment change only if new values are passed. That is exactly the kind of consequence detail annotations cannot encode, and it is the highest-value information for a destructive operation.

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?

Three tight sentences, front-loaded with what the tool does and the destructive consequence, then the scope restriction, then the argument relationship. No filler and nothing buried.

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?

For a destructive 12-parameter mutation with no output schema, the description covers the irreversibility, the item-indexing convention, the selective field overwrite, and the scope boundary, while the 100%-covered schema handles argument syntax. Nothing an agent needs before invoking this safely is 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 the baseline is 3, but the description adds semantics beyond the schema: the exact meaning of `item` (1-based position counting notes) and the conditional behavior that title/comment are only overwritten when new values are supplied. It also frames the remaining arguments as identical to add_screenshot, reducing the need to re-read them.

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 precise verb and resource ('Overwrite one existing screenshot in a review with a new capture, in the same position') and immediately distinguishes itself from siblings by declaring 'Works on screenshots only, not notes.' An agent can separate this from add_screenshot or add_note without opening any schema.

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

Usage Guidelines4/5

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

Gives clear context — replacing an existing item in place rather than appending — and routes the agent to add_screenshot for the shared capture arguments. It does not explicitly state the inverse condition ('use add_screenshot when you want a new item'), so the when-to-choose guidance is implied rather than spelled out.

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

All Cobalt Capture toolsInspect
Try in Browser
One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Glama MCP Gateway

Add one secure layer between your agents and this server.

Resources