JsonlView

A read-only event data studio for VS Code.

JsonlView turns large JSONL and NDJSON files into a workbench for logs, telemetry, traces, and coding-agent runs. Browse physical records quickly, understand their meaning, and inspect the exact source without changing the file.

Why JsonlView

JSONL is easy for programs to append and difficult for people to inspect. A single file can contain thousands of records, malformed lines, tool calls, trace events, and long agent messages. JsonlView keeps the physical record authoritative while adding bounded indexing, semantic views, and deliberate detail loading.

See It

The same workbench adapts to different event shapes while keeping the source record available in Raw.

The screenshots use public-shaped, redacted fixtures prepared in the companion harness; they contain no private transcript bodies or machine paths.

Event analysis

Record detail

Telemetry schema

Agent profile timelines

Diff and prompt detail

What You Get

• Fast bounded browsing: byte-aware indexing, virtualized pages, lazy detail hydration, and BigInt-safe ordinals for large files.
• Views for different questions: Table, Timeline, Schema, Problems, Insights, Tree, Raw, Derived, and Bytes.
• Useful semantics: automatic profiles for Codex, Claude Code, pi coding agent, OpenTelemetry, structured application logs, software-engineering trajectories, and generic JSONL fallback.
• Provider-aware details: tool results, diff and patch payloads, thinking, checkpoints, and nested system prompt sections remain inspectable in the shared Tree, Raw, Markdown, and JSON detail surfaces.
• Safe inspection: malformed records remain visible, unknown events fall back to generic JSON, and the exact source stays available for copying.
• Focused analysis: typed filters, text search, physical paging, row-order control, bounded category/time Insights, and an opt-in tail Follow mode.
• Agent session navigation: an optional read-only tree for supported local Codex, Claude, and pi session homes, with parent/child relationships and incremental loading.

Session Navigator (opt-in)

Enable jsonlView.sessionNavigator.enabled only when you want a local, metadata-bounded view of supported agent session homes. It starts disabled, asks for explicit source authorization, and keeps transcript bodies in their provider files.

Source entry

Install

Choose one registry build for the VS Code installation.

| Registry | Extension identity | | --- | --- | | Open VSX | Sumi-Sophia.jsonl-view | | Visual Studio Marketplace | Sumi-Sophia.jsonlview-data-studio |

You can also open the VS Code Extensions view and search for JsonlView Data Studio. The extension requires VS Code 1.136 or newer and file-backed random access; virtual workspaces are not supported in this release.

A Real Use Path

1. Open a .jsonl or .ndjson file in VS Code. Use Open With when another editor is registered for the file type.
2. Start in Table to scan records. Switch to Timeline, Schema, or Problems when the shape or data quality needs a different view.
3. Select a record to open the detail drawer. Use Tree for structure, Raw for the exact source, Derived for bounded semantic fields, and Bytes for physical offsets.
4. Apply a profile when the automatic suggestion needs confirmation. Profiles add labels and fields; they do not rewrite the JSONL record.
5. Enable Follow when a producer appends to the file. Use Insights only when you need bounded aggregate counts or time buckets.
6. Enable Session Navigator in settings when you want local agent sessions. Standard Codex, Claude, and pi homes can be detected after opt-in; other roots can be added explicitly from the Navigator.

Opt-In Product Lines

The editor is read-only by default. The following surfaces are deliberately opt-in or disabled by default:

| Surface | Default | What it does | | --- | --- | --- | | Profile auto-detection | On | Suggests a semantic view from bounded samples. | | Follow | Off | Tracks an append-only tail after an explicit action. | | Insights | On demand | Runs a bounded aggregate scan only when opened or refreshed. | | Session Navigator | Off | Reads supported local agent metadata after authorization. | | Native newline scanner | Off | Probes the optional accelerator only when configured. | | MCP navigation contract | Disabled | Keeps the experimental metadata adapter out of runtime transports. | | OTLP export | Disabled | Keeps observability export out of the product until separately enabled. |

Privacy And Source Authority

• JsonlView never edits the source file, executes its contents, or requires a network connection to browse it.
• Indexes, session catalog rows, and Webview projections are disposable metadata. The source JSONL remains the authority.
• Record hydration is bounded. Raw and Copy preserve the available source value when a structured view is incomplete or ambiguous.
• Session Navigator reads local provider metadata only after opt-in and keeps transcript bodies out of its catalog.
• MCP and OTLP are disabled experimental boundaries in this release; no network listener is created by the default product path.

See format and profile boundaries for the exact contract and unsupported formats.

Supported Boundary

The current physical adapter accepts file-backed .jsonl and .ndjson. It does not claim regular JSON arrays/objects, multiline text logs, compressed JSONL, OTLP protobuf, or Chrome/Jaeger trace JSON as drop-in formats. Those formats need their own framing and authority rules; see the format boundary.

Semantic profiles are additive. They can identify common Codex, Claude Code, pi, OpenTelemetry, application-log, and Agent fields, but unknown records stay available through the generic view. The observed Claude and agent surface rules are compatibility behavior, not a promise that a producer's private schema is stable.

Roadmap Preview

The next architecture work is staged and evidence-led:

• Runtime-bounded decomposition and toolchain ownership keeps the extension host, Webview, engine, profiles, and native scanner under explicit ownership while preserving the current facade.
• Architecture evolution slices proposes barrel export isolation, test colocation, and staged vertical migration as small reversible steps.
• Acceleration roadmap measures optional native scanning and future query work against the portable implementation before any capability becomes a default.

These are roadmap decisions and experiments, not promises to mutate source files, add a network service, or split the product into packages before a second consumer and release contract justify it.

Documentation

• Format and profile boundaries
• Decision records
• Release and publication notes
• Changelog

Development

The repository uses the Node version declared by .node-version and the pnpm version declared by package.json.

pnpm install --frozen-lockfile
pnpm check:contract
pnpm typecheck
pnpm test
pnpm build

License

JsonlView is available under the MIT License. Third-party licenses and notices are listed in THIRD-PARTY-NOTICES.txt.