Machine Learning · head to head
Comet ML vs PromptLayer
Comet ML
Machine Learning
Platform for tracking, comparing, and optimizing ML experiments
- From
- Free
- Free plan
- Yes
PromptLayer
AI
Collaboration platform for prompt management, evaluation, and observability
- From
- Free
- Free plan
- Yes
The short version
- Each has a real cost: Comet ML the free cloud tier caps data at 25,000 spans a month with 60 day retention; PromptLayer the free plan is capped at only 2,500 requests per month, quite limited for active production use.
- They diverge on capability: Comet ML covers Experiment tracking, PromptLayer covers Visual prompt management.
- Prices and features above were last checked on 30 August 2026.
Where they differ
Only the attributes on which Comet ML and PromptLayer actually diverge.
| Attribute | Comet ML | PromptLayer |
|---|---|---|
| Platforms | Web, Linux, Mac, Windows | web, api |
| Category | Machine Learning | AI |
| Founded | 2017 | Unknown |
Identical on both: starting price (Free), pricing model (freemium), free tier (Yes), user rating (Not yet rated).
What each one covers
Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.
Only in Comet ML
- Experiment tracking
- Code versioning
- Model registry
- Hyperparameter optimization
- Production monitoring
- PyTorch
- TensorFlow
- Keras
Only in PromptLayer
- Visual prompt management
- Agent observability
- Evaluations
- Version control
- Cost and latency monitoring
- Agent workflow tracing
What people use each for
The jobs each tool is most often brought in to do.
Comet ML
- LLM observability and monitoringnot PromptLayer
- AI agent testing and debuggingnot PromptLayer
- Experiment tracking for machine learningnot PromptLayer
- Model registry and version managementnot PromptLayer
- ML model training monitoringnot PromptLayer
PromptLayer
- Versioning and deploying prompts without code redeploysnot Comet ML
- Running evaluations with human review before production releasenot Comet ML
- Tracing multi-step agent workflows for debuggingnot Comet ML
- Monitoring LLM cost and latency by featurenot Comet ML
Where each one falls short
Documented limitations, not opinions. Every one is a constraint you would hit in normal use.
Comet ML
- The free cloud tier caps data at 25,000 spans a month with 60 day retention
- Retention stays at 60 days even on the paid Pro plan, and extending it is a $29 per 100k spans add on
- Overage on Pro is $5 per additional 100,000 spans
- The free MLOps tier is a single user with 100 GB of storage and training hours governed by a fair usage policy
- Pro MLOps is $19 per user per month and caps the team at 10 users
PromptLayer
- The free plan is capped at only 2,500 requests per month, quite limited for active production use.
- The Team plan jumps to $500/month, a large step up from the $49/month Pro plan.
- Overage transaction fees apply on top of subscription costs, which can make total spend less predictable.
- Enterprise-grade features like HIPAA BAAs and custom deployment require contacting sales.
Pricing, plan by plan
Comet ML
Free- Free CloudFree
- Up to 10 team members
- 25,000 spans per month
- 60-day data retention
- Pro Cloud$19/month
- Up to 50 team members
- 100,000 spans per month
- 60-day data retention
- MLOps FreeFree
- 1 user with fair usage policy
- Experiment tracking
- Dataset management
- MLOps Pro$19/user/month
- Up to 10 users
- 1,500 training hours included
- 500GB storage included
PromptLayer
Free- FreeFree
- 5 users
- 2,500 requests/month
- 1 workspace
- Pro$49/month
- Unlimited playgrounds and workspaces
- 150MB datasets
- Pay-as-you-go overage at $0.003/transaction
- Team$500/month
- 25 users
- 100k+ monthly requests
- Webhooks
- Enterprise$undefined/mo
- Custom limits
- Role-based access controls
- HIPAA with BAA
Which should you pick?
Choose Comet ML if
- You need experiment tracking.
- You want to start without paying.
- You work on Web, Linux, Mac, Windows.
- You also want code versioning.
Choose PromptLayer if
- You need visual prompt management.
- You want to start without paying.
- You work on web, api.
- You also want agent observability.
Questions people ask
- Is Comet ML or PromptLayer better?
- Neither clearly leads. Comet ML starts at Free and PromptLayer at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
- Which is cheaper, Comet ML or PromptLayer?
- Comet ML starts at Free and PromptLayer at Free.
- Does Comet ML or PromptLayer run on more platforms?
- Comet ML runs on Web, Linux, Mac, Windows. PromptLayer runs on web, api.
- Can I use Comet ML for free?
- Both have a free tier, so you can try either at no cost before committing.
- What is Comet ML best used for?
- Comet ML is most often used for llm observability and monitoring, ai agent testing and debugging, experiment tracking for machine learning, model registry and version management. Of those, llm observability and monitoring and ai agent testing and debugging are not what PromptLayer is typically brought in for.
- What can Comet ML do that PromptLayer cannot?
- Comet ML covers Experiment tracking, Code versioning, Model registry, Hyperparameter optimization. PromptLayer covers Visual prompt management, Agent observability, Evaluations, Version control.
Answered from the vendors’ own pages
Comet ML: Does Comet.ml offer a free plan?
Yes, Comet.ml offers free tiers for both Opik (cloud observability) and MLOps platforms. Free Cloud Opik includes up to 10 team members and 25,000 spans/month. Free MLOps tier is limited to 1 user.
SourcePromptLayer: What does PromptLayer cost?
PromptLayer has a free plan, a Pro plan at $49/month, a Team plan at $500/month, and custom Enterprise pricing, with additional usage billed per transaction beyond plan limits.
SourceComet ML: How many team members can use the free Comet.ml tier?
Free Cloud supports up to 10 team members. The Pro Cloud plan supports up to 50 team members at $19/month.
SourcePromptLayer: Is there a free plan, and what are its limits?
The Free plan includes 5 users, 2,500 requests per month, 1 workspace, 250 monthly eval cell executions, and datasets up to 10MB.
SourceComet ML: What is a span in Comet.ml pricing?
A span represents a single tracked operation such as model requests or function calls. Free Cloud tier includes 25,000 spans per month.
SourcePromptLayer: How is usage metered beyond the plan limits?
Additional usage is charged per transaction for requests, agent runs, and evaluation cell runs, at $0.003/transaction on Pro and $0.002/transaction on Team.
SourceComet ML: Does Comet.ml offer academic pricing?
Yes, a free Pro plan is available for academic users; verification is required via signup.
SourceRelated pages
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