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Sentry · Task agent

Junior

An open-source Slack agent built at Sentry that acts like an intern; takes tasks, retrieves context across many company systems, and is steered and reviewed by humans. Its CEO argues one general-purpose agent beat several vendor-specific bots.

1 Supports2 Supports3 Contextualizes

Approach type
Task agent
Work
Coding, Code review, Support, On-call
Human involvement
Human in loop
Invocation
Event driven, Interactive
Interfaces
Slack, Web, Github
Deployment stage
Deployed
Evidence strength
Detailed primary
Entry reviewed

How it works

The workflow the sources report for this implementation.

searchMcpTools loads tools on demand instead of dumping every schema into the prompt

1

Credentials injected host-side; the sandbox/model never touches a secret

1

Survives serverless timeouts via a queue + claim model

1

Where people stay involved

  • assigned task → human-steered and reviewed outputContinuous steering · Level 2

Level 2 for assigned task → human-steered and reviewed output; human attention boundary: continuous-steering.

1

Observation date
2026

Implementation details

Sandbox

Vercel serverless functions; Vercel agent-browser sandbox with an on-path proxy for traffic interception; ephemeral containers

1

Harness

Custom harness on Pi's SDK; a task broker over Vercel Queues with an inbox -> worker-claim -> interrupt/resume pattern to survive serverless timeouts; 'skills-as-runbooks'

1

Model

Claude Sonnet (faster); swappable (Opus as a more expensive option)

1

Interfaces

slack, web, github

1

Tool access

Progressive discovery via MCP; by default Junior connects to no provider until the agent requests a tool lookup; plugins connect Sentry, GitHub, Linear, Notion

1

Knowledge

Conversation transcripts persisted in Redis; repo search to trace code paths; skill docs (TELEMETRY.md, SOUL.md)

1

Credentials

On-path proxy injection; the model never sees the token because it is not in the sandbox; plugins declare OAuth flows and credential domains; GitHub distinguishes read vs. write

1

Context management

Incremental transcript updates in Redis; resource subscriptions to GitHub PR events for follow-ups

1

Reported results and limitations

The catalog records what the sources report, with the scope and the denominator of every figure. A qualification below limits the figure it sits under.

Reported metrics

Headline claim

Open-source (Apache-2.0) Slack agent (~100k lines of TS) used internally at Sentry

1 Supports4 Supports

The source does not report the denominator of this figure.

Reported by
Sentry
Scope
Junior codebase size and license in the author report
Key observation

Around 100,000 lines of TypeScript excluding tests, evals, docs, and lockfiles

1

The source does not report the denominator of this figure.

Reported by
Sentry
Scope
TypeScript lines in Junior excluding tests, evals, documentation, and lockfiles
Key observation

4 months from start to writeup

1

The source does not report the denominator of this figure.

Reported by
Sentry
Scope
Author-reported development and iteration time before the writeup

Lessons and interpretation

One general-purpose agent connected to many company systems beats several vendor-specific bots

1

Skills-as-runbooks encode operational knowledge the agent can follow

1

Stateless compute fights you; serverless functions time out and disappear; model the agent around interrupt/resume

1

Unit tests are the wrong yardstick for agents; invest in evals and integration tests instead

1

Writes need per-user authorization, not blanket trust

1

Sources and research details

Citations link to the original publisher. Each source also keeps a preserved copy in the repository, so a changed or removed page stays checkable.

  1. Building an Intern (Junior at Sentry)https://cra.mr/building-an-intern/Engineering blog · First party · Last source verification: 2026-08-31
    Preserved copy ↗
  2. getsentry/junior source repositoryhttps://github.com/getsentry/juniorRepository · First party · Last source verification: 2026-08-31
    Preserved copy ↗
  3. Sentry Labshttps://labs.sentry.dev/Documentation · First party · Last source verification: 2026-08-31
    Preserved copy ↗
  4. getsentry/junior Apache 2.0 licensehttps://github.com/getsentry/junior/blob/main/LICENSE?plain=1Source code · First party · Last source verification: 2026-08-31
    Preserved copy ↗
Research details for every claim on this page
  1. Summary
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  2. Headline claim
    Statement type
    Metric
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
    Reported by
    Sentry
    Scope
    Junior codebase size and license in the author report
    Denominator
    Not reported
    Method
    Not reported
    Observation date
    Not reported
  3. Sandbox
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  4. Harness
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  5. Model
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  6. Interfaces
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  7. Tool access
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  8. Knowledge
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  9. Credentials
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  10. Context management
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  11. Supporting component
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  12. Supporting component
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  13. Supporting component
    Statement type
    Fact
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
  14. Key observation
    Statement type
    Metric
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
    Reported by
    Sentry
    Scope
    TypeScript lines in Junior excluding tests, evals, documentation, and lockfiles
    Denominator
    Not reported
    Method
    Not reported
    Observation date
    Not reported
  15. Key observation
    Statement type
    Metric
    Provenance
    Reported
    Confidence
    High
    Confidence reason
    A linked first-party source states the claim.
    Reported by
    Sentry
    Scope
    Author-reported development and iteration time before the writeup
    Denominator
    Not reported
    Method
    Not reported
    Observation date
    Not reported
  16. Lesson
    Statement type
    Inference
    Provenance
    Catalog judgment
    Confidence
    Medium
    Confidence reason
    The catalog derives this observation from the linked sources.
  17. Lesson
    Statement type
    Inference
    Provenance
    Catalog judgment
    Confidence
    Medium
    Confidence reason
    The catalog derives this observation from the linked sources.
  18. Lesson
    Statement type
    Inference
    Provenance
    Catalog judgment
    Confidence
    Medium
    Confidence reason
    The catalog derives this observation from the linked sources.
  19. Lesson
    Statement type
    Inference
    Provenance
    Catalog judgment
    Confidence
    Medium
    Confidence reason
    The catalog derives this observation from the linked sources.
  20. Lesson
    Statement type
    Inference
    Provenance
    Catalog judgment
    Confidence
    Medium
    Confidence reason
    The catalog derives this observation from the linked sources.
  21. Operating model assessment
    Statement type
    Inference
    Provenance
    Catalog judgment
    Confidence
    High
    Confidence reason
    The source explicitly describes humans steering and reviewing the agent throughout its work.
    Observation date
    2026
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