Context Usage

An OpenCode TUI plugin that adds a /context command: the exact breakdown behind the built-in Context panel, plus the session-wide usage and cost totals OpenCode tracks internally — including delegated subagent sessions.

Example output

The examples below use illustrative numbers.

Simple session

Context usage — Refactoring the auth middleware
provider/model · build

Context window (last request)
  Input (no cache)                       83
  Output                              1,012
  Reasoning                             342
  Cache read (hits)                 118,528
  Total                   119,965 / 1M (12%)

Session total — 29 turns · 4 prompts
  Input (no cache)                  156,297
  Output                             31,389
  Reasoning                          28,405
  Cache read (hits)               1,808,128
  Total                           2,024,219
  Cache hit rate                     92.0%
  Cost                           $0.043687

Session with delegated subagents

When the agent delegates work with task, each subagent runs in its own child session. The plugin walks that tree and adds two extra blocks:

Context usage — Fixing the checkout flow
provider/model · build

Context window (last request)
  Input (no cache)                       83
  Output                              1,012
  Reasoning                             342
  Cache read (hits)                 118,528
  Total                   119,965 / 1M (12%)

Session total — 29 turns · 4 prompts
  Input (no cache)                  156,297
  Output                             31,389
  Reasoning                          28,405
  Cache read (hits)               1,808,128
  Total                           2,024,219
  Cache hit rate                     92.0%
  Cost                           $0.043687

Subagents — 1 session
  Input (no cache)                   41,002
  Output                             18,544
  Reasoning                          12,301
  Cache read (hits)               1,092,999
  Total                           1,164,846
  Cache hit rate                     96.4%
  Cost                           $0.034800

Combined total — session + subagents
  Total                           3,189,065
  Cost                           $0.078487

Why

OpenCode's sidebar Context panel mixes two different scopes: tokens and % used are a snapshot of the last request, while spent is the session total. There is no built-in way to see the accumulated traffic of a session either.

This plugin makes both scopes explicit and shows the arithmetic behind each number, so you can answer questions like:

• How full is my context window right now?
• How many tokens have actually passed through the API in this session?
• How much of the prompt is served from cache, and how much of the cost is cache vs fresh tokens?
• How much did the subagents I delegated work to consume? (OpenCode tracks each subagent — task calls — in its own child session, excluded from the parent's totals. The plugin walks the delegation tree and shows the combined total.)

It reads the already-synced TUI state (api.state.session), so it is instant, never calls an LLM and has zero runtime dependencies.

Install

opencode plugin opencode-context-usage

OpenCode installs the package and adds it to your tui.json. Or add it manually (global ~/.config/opencode/tui.json or project .opencode/tui.json):

{
  "$schema": "https://opencode.ai/tui.json",
  "plugin": ["opencode-context-usage"]
}

Restart OpenCode after changing tui.json (TUI plugins load at startup).

Usage

Open a session and run:

/context

Alias: /ctx. Close the dialog with Esc or Ctrl+C.

Command name

The command defaults to /context. If another command already uses that slash name (for example a future built-in /context), the plugin automatically registers as /context-usage instead. You can also set the name explicitly:

{
  "plugin": [["opencode-context-usage", { "slash": "usage" }]]
}

How the numbers are computed

OpenCode normalizes provider usage in Session.getUsage: input excludes cache tokens and output excludes reasoning tokens.

Metric	Meaning
Input (no cache)	Prompt tokens not served from cache
Output	Generated tokens excluding reasoning (includes tool calls)
Reasoning	Reasoning / thinking tokens
Cache read (hits)	Prompt tokens served from cache
Cache write	Prompt tokens written to cache (row hidden when 0)
Total (window)	input + output + reasoning + cache read + cache write of the last completed request — the same number the built-in panel shows
Cache hit rate	cache read / (input + cache read + cache write)
Cost	Sum of the per-turn costs OpenCode records for the session (session.cost)
Subagents	Aggregated usage of every child session delegated from this one (recursively)
Combined total	Session total + subagents total (tokens and cost)

Session totals come from the authoritative session aggregate that OpenCode stores (the same source the built-in panel uses), not from re-summing the messages loaded in the TUI. On long sessions the TUI keeps only a window of recent messages, so the turn and prompt counts may show a + (for example 95+ turns) to indicate there are more messages than the loaded window. Subagent totals use the same session aggregates for each child session, so they are exact.

Compatibility

• OpenCode >= 1.18.0 < 2 (TUI plugins via tui.json).
• Subagent totals use the session children endpoint. If your build does not expose it, the plugin simply hides the subagents and combined blocks.
• The TUI plugin API is young and may change between OpenCode versions. If something breaks, please open an issue with your OpenCode version.

Development

npm install
npm run typecheck
npm test        # builds dist/ and runs the unit tests
npm run build

To try a local checkout in OpenCode, point tui.json at the built file:

{
  "plugin": ["/absolute/path/to/opencode-context-usage/dist/tui.js"]
}

License

MIT